Dr. Jeff Masters' WunderBlog

Tomas significantly weaker; damage very heavy on St. Lucia and neighboring islands

By: JeffMasters, 6:38 PM GMT on October 31, 2010

Hurricane Tomas dealt a punishing blow to the Caribbean island of St. Lucia, with the neighboring islands of St. Vincent, Dominica, and Barbados also suffering heavy damage. St. Lucia received the full brunt of the northern eyewall of Tomas as it intensified into a Category 2 hurricane with 100 mph winds early this morning. The St. Lucia weather service reported that sustained winds of 90 - 95 mph affected the island. A state of emergency has been declared on the island, and there are island-wide power outages on both St. Lucia and Dominica. Heavy flooding affected St. Lucia, washing out many bridges, and the airport is closed due to flooding. Damage to structures is considerable, with many roofs gone, and damage reported to hospitals, schools, and businesses.


Figure 1. Torrential rains from Tomas triggered massive flooding on St. Lucia that destroyed several bridges and severely damaged roads. Image credit: Caribbean Hurricane Network.

Tomas significantly weakens
An Air Force hurricane hunter aircraft arrived at Tomas at 2pm this afternoon, and found a much weaker storm. The 2pm EDT center fix found that the pressure has risen to 994 mb, and the strongest surface winds were barely Category 1 hurricane strength, 74 mph. The aircraft found the the eyewall had mostly collapsed. Satellite loops of Tomas also show a significant degradation in the appearance of the storm in recent hours. The storm is highly asymmetric with very little heavy thunderstorm activity or upper level outflow on the west side, and the hurricane has only one prominent spiral band, on the east side. Wind shear is a high 20 knots due to strong upper level west-southwest winds, and these winds are driving dry air at mid-levels of the atmosphere into Tomas' west side, as seen on water vapor satellite imagery.


Figure 2. MODIS satellite image of Tropical Storm Tomas taken at 10:30am EDT Saturday October 30, as the storm began lashing the Lesser Antilles. At the time, Tomas was a Category 1 hurricane with 75 mph winds. Image credit: NASA.

Track forecast for Tomas
The ridge of high pressure pushing Tomas to the west-northwest will weaken by Tuesday, as a trough of low pressure approaches the eastern U.S. and breaks down the ridge. This will result in Tomas slowing from its current 9 mph forward speed to 5 mph by Tuesday. By Thursday, the trough to Tomas' north should be able to pull the storm to the north. The exact timing and location of this turn is still very uncertain. The computer model solutions from the latest set of 8am EDT (12Z) runs include a strike on Haiti on Friday (GFS and GFDL models), a strike on the Dominican Republic on Friday (NOGAPS model), a strike on Haiti on Saturday (UKMET model), a strike on Jamaica and eastern Cuba on Thursday (Canadian), or a strike on Puerto Rico on Friday (HWRF).

Intensity forecast for Tomas
Wind shear is forecast to remain in the high range, 20 - 25 knots, through Monday night, then decline to the moderate range, 10 - 20 knots, for the remainder of the week. Tomas will struggle with the shear and the dry air to its west through Tuesday, and I expect it will weaken to a tropical storm tonight, and remain a tropical storm until Tuesday, when the shear finally relents. At that point, re-intensification is likely, though with the storm's inner core gone, I expect it will take Tomas two days before it can re-establish a complete eyewall. Hindering that process will be the slow motion of the storm, which will allow cooler waters from the depths upwell to the surface and cool the SSTs. Still, the waters are very warm in the Caribbean and these waters extend to great depth, so the upwelling cool water may not impede intensification as much as might ordinarily be expected. The intensity Tomas might have as landfall in Hispaniola or Jamaica is highly uncertain, and a strength anywhere between a tropical storm and Category 3 hurricane would not be surprising. The HWRF model predicts Tomas will be a borderline tropical storm/Category 1 hurricane on Friday, while the GFDL foresees Tomas will be a strengthening Category 3 hurricane as it bears down on Haiti Friday afternoon. I predict Tomas will have trouble reorganizing, and will be a strengthening Category 1 hurricane on Friday as it makes landfall in Haiti or the Dominican Republic.


Figure 3. Hurricane specialists Robbie Berg (background) and Dan Brown (foreground) discuss the latest data on Tomas Friday night at the National Hurricane Center.

Next update
I'll have an update Monday morning.

Jeff Masters

Hurricane

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Unprecedented Hurricane Tomas pounding the Lesser Antilles

By: JeffMasters, 3:38 PM GMT on October 30, 2010

Hurricane Tomas, an unprecedented Lesser Antilles hurricane for so late in the season, is bearing down on the islands of St. Lucia and St. Vincent with Category 1 winds of 75 mph. Recent radar imagery from the Martinique radar shows that Tomas is still in the organizing stage, with an eyewall that just closed off, and a weak area of echoes on the south side, due to modest wind shear of 10 knots caused by southerly upper-level winds. The Hurricane Hunters reported top surface winds in the northern eyewall near 75 mph. St.Lucia figures to get the worst blow from Tomas, as this island will experience the strong right-front quadrant of the storm--the north eyewall. Winds on the island were sustained at 46 mph, gusting to 67 mph, at 11am EDT. Winds at Barbados peaked at 37 mph, gusting to 56 mph, early this morning, and the pressure bottomed out at 994 mb. Satellite loops of Tomas show a large and well-organized Cape Verdes-type hurricane, with good upper level outflow on all sides except the south, and an impressive amount of heavy thunderstorm activity. This is a very dangerous hurricane that is just beginning to get going. You can follow the progress of Tomas through the islands today with our wundermap zoomed in on St. Lucia.


Figure 1. Morning radar image from the Martinique radar shows the eye of Tomas moving between the islands of St, Lucia to the north and St. Vincent and the Grenadines to the south. The southern portion of the eyewall had just closed off with this image. Image credit: Meteo France.

Intensity forecast for Tomas
Now that the eyewall of Tomas has completely closed off, a period of steady and possibly rapid intensification lasting until Sunday afternoon is likely. The intensification rate may then be slowed by an increasing flow of southwesterly upper-level winds, which are expected to bring dry air and a moderate 15 - 20 knots of wind shear to Tomas Sunday through Tuesday, according to the latest SHIPS model forecast. Shear is then expected to relent, allowing more intensification on Wednesday. Water temperatures are a record warm 29.5°C and the Tropical Cyclone Heat Potential--a measure of the total heat content of the ocean--is a very high 100 kJ/cm^2, which is very favorable for rapid intensification. I expect the Tomas will strengthen to a Category 3 or 4 hurricane by Wednesday.


Figure 2. Hurricane specialists Robbie Berg (background) and Dan Brown (foreground) discuss the latest data on Tomas last night at the National Hurricane Center.

Track forecast for Tomas
The computer models have come into better agreement this morning that after Tomas reaches the central Caribbean 4 - 5 days from now, a turn to the north or northeast is likely, in response to a strong trough of low pressure expected to develop over the Eastern U.S. The exact timing of this turn to the north or northeast is difficult to predict at this time, as steering currents will be weak in the Caribbean after Tomas passes through the Lesser Antilles today and Sunday. At this time, is appears that the Dominican Republic and Haiti are most at risk from a strike by Tomas, though the storm could move as far west as Jamaica, or as far east as the northern Lesser Antilles Islands.


Figure 3. Hurricane specialist Dan Brown computes Tomas' radius of tropical storm force winds using the old-fashioned paper track plot and dividers technique. Hurricane specialists at NHC commonly use a paper track plot to mark all storm center fixes and compute the current motion of the storm. A storm's current heading and speed in NHC advisories is usually a 12-hour average of the motion up until the final fix position.

Tomas, Shary, and the 2010 hurricane season in perspective
Tomas' formation ties 2010 with 1995 and 1887 for 3rd place for most number of named storms in an Atlantic hurricane season. Only 2005 (28 named storms) and 1933 (21 named storms) were busier. Atlantic hurricane records go back to 1851, though there were likely many missed named storms prior to the beginning of satellite coverage in the mid-1960s. The intensification of Shary and Tomas into hurricanes today brings the total number of hurricanes this season to twelve, tying 2010 with 1969 and 1887 for second place for most hurricanes in a season. The record is held by 2005 with fifteen hurricanes, and I don't think we'll beat that record this year!

The formation of Tomas so far south and east this late in the season is unprecedented in the historical record; no named storm has ever been present east of the Lesser Antilles (61.5°W) and south of 12°N latitude so late in the year. Hurricane Six of 1896 came close--it was also a tropical storm south of 12°N and east of 61.5°W on October 29, but nine hours earlier in the day. That storm recurved to the north and missed the Lesser Antilles. Tomas' track through the southern Lesser Antilles so late in the year is unprecedented. There have been only two other tropical storms that formed after October 15 south of 12°N and east of 61.5°W: Hurricane Jose, which was a tropical storm in that region on October 18, 1999, and Tropical Storm Nicolas, on October 16, 2003. Tomas most reminds me of a storm I flew into with the Hurricane Hunters--Hurricane Joan of 1988, which was a tropical storm on October 14 near Tomas' current location, and later strengthened into a Category 4 hurricane that hit Nicaragua. According to Chenoweth (2008), Tomas is the first tropical storm to cross through the Lesser Antilles Islands south of 16°N this late in the year since 1724. In that year, a tropical storm on 12 November crossed the islands at 13.7°N 61.5°W, and later became a hurricane that affected Jamaica. There was also a hurricane on 30 October 1671 that crossed 61.5°W at 13.3°N, and did damage on Barbados.

Another unusual aspect of Tomas' formation is that we now have two simultaneous hurricanes in the Atlantic Ocean on October 30. There has been only one hurricane season since 1851 that had had two simultaneous hurricanes later in the year--1932, when Hurricane Ten and Hurricane Eleven both existed November 7 - 10. Today is also the 5th latest date in the season that there have been two simultaneous named storms in the Atlantic. The record was set way back in 1887, when Hurricane Eighteen and Tropical Storm Nineteen were both active on December 8. There were three years that had simultaneous November named storms: 1932, 1961, and 2001.

References
Chenoweth, M. and D. Divine (2008), "A document-based 318-year record of tropical cyclones in the Lesser Antilles, 1690-2007", Geochemistry, Geophysics, Geosystems, 9, doi:10.1029/2008GC002066.

Next update
I'll have more on Sunday by 3pm EDT. I'm headed home to Michigan today, after a very valuable week here at the National Hurricane Center. The experience gave me a new appreciatation for just how good the forecasters are at what they do. NHC's hurricane experts are truly world-class, and we are very fortunate to have such a talented group of hard-working forecasters keeping us informed on the dangers we face from Atlantic hurricanes.

Jeff Masters

Hurricane

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Strengthening Tomas headed for the Lesser Antilles

By: JeffMasters, 1:27 AM GMT on October 30, 2010

Tropical Storm Tomas has exploded into existence in spectacular fashion, becoming the nineteenth named storm of this amazingly active 2010 Atlantic hurricane season. I'm reporting to you live from the National Hurricane Center tonight, where forecasters are working hard to stay abreast of Tomas' intensification. Three hurricane specialists are on duty tonight--Dave Roberts, who is handling Tropical Storm Shary, and Robbie Berg and Dan Brown, who are focusing on Tomas. The Hurricane Hunters have just left Tomas, as of 8pm EDT, and they found a significant increase in winds. Winds at their 1500 foot flight level were 70 mph, and surface winds as measured by the SFMR instrument were near 60 mph. This supports an increase in Tomas' winds to 60 mph in tonight's 8pm EDT public advisory. Since this is such a large increase in intensity from what was forecast--Tomas was not supposed to have 60 mph winds for another 24 hours--this necessitates issuance of a special advisory package. A full set of forecast maps, a marine advisory, wind probability forecast, and a discussion just went out to the world. While all this was occurring, several phone calls to Barbados, St. Lucia, and Martinique were made, alerting the islands to the fact that a Hurricane Warning may be required with the 11pm advisory tonight. NHC has both French speaking and Spanish speaking meteorologists on staff that can coordinate with the islands that don't have English as their main language. I listened in on a 5-minute conversation in French between the weather service in Martinique and NHC meteorologist Mike Tichacek, as they discussed when Martinique may want to issue a Hurricane Warning.


Figure 1. Warren VonWerne (right) of CARCAH presents the latest data from the Air Force Hurricane Hunters to hurricane specialist Robbie Berg.

Intensity forecast for Tomas
The forecasters at NHC are puzzling over the latest intensity forecasts for Tomas. The latest intensity forecast from the GFDL, HWRF, and SHIPS models are not that impressive, and they keep Tomas as a strong tropical storm or weak hurricane for the next five days. The wind shear forecast from SHIPS is particularly odd--the latest 18Z forecast predicts high wind shear of 20+ knots beginning Sunday morning, and the previous SHIPS forecast held wind shear below 15 knots for the next five days. The latest runs by the GFS, ECMWF, and UKMET models all show a very favorable environment for intensification over the next five days over the Caribbean, with Tomas positioning itself beneath an upper level high in a light wind shear environment. The best bet is that Tomas will intensify into a major hurricane over the Central Caribbean by early next week.


Figure 2. NHC meteorologist Mike Tichacek discusses the latest intensity forecast for Tomas with the Martinique weather service (in French.) In the background, hurricane specialist Dave Roberts works on advisories for Tropical Storm Shary.

Track forecast for Tomas
After Tomas reaches the central Caribbean 4 - 6 days from now, there are two possible track scenarios depicted by the models--a continued westerly motion towards Nicaragua, or a sharp turn to the north, with a track over Hispaniola or Puerto Rico. Steering currents will be weak, and we'll just have to wait and see how the steering currents evolve.

Tomas' formation location unprecedented this late in the season
Tomas' formation ties 2010 with 1995 and 1887 for 3rd place for most number of named storms in an Atlantic hurricane season. Only 2005 (28 named storms) and 1933 (21 named storms) were busier. Atlantic hurricane records go back to 1851, though there were likely many missed named storms prior to the beginning of satellite coverage in the mid-1960s.

The formation of a tropical storm so far south and east this late in the season is unprecedented in the historical record; no named storm has ever been present east of the Lesser Antilles (60°W) and south of 12°N latitude so late in the year. Hurricane Six of 1896 came close--it was also a tropical storm south of 12°N and east of 60°W on October 29, but nine hours earlier in the day. That storm recurved to the north and missed the Lesser Antilles. Tomas' track through the southern Lesser Antilles so late in the year is unprecedented. There have been only two other tropical storms that formed after October 15 south of 12°N and east of 60°W: Hurricane Jose, which was a tropical storm in that region on October 18, 1999, and Tropical Storm Nicolas, on October 16, 2003. Tomas most reminds me of Hurricane Joan of 1988, which was a tropical storm on October 14 near Tomas' current location, and later strengthened into a Category 4 hurricane that hit Nicaragua.

Another unusual aspect of Tomas' formation is that we now have two simultaneous named storms in the Atlantic Ocean on October 29. There have been only four hurricane seasons since 1851 that have had two simultaneous named storms later in the year. The record was set way back in 1887, when Hurricane Eighteen and Tropical Storm Nineteen were both active on December 8. There were three years that had simultaneous November named storms: 1932, 1961, and 2001.

Next update
I'll have more late Saturday morning.

Jeff Masters

Hurricane

Updated: 1:32 AM GMT on October 30, 2010

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Shary forms; potentially dangerous 91L approaching Lesser Antilles

By: JeffMasters, 3:23 PM GMT on October 29, 2010

Tropical Storm Shary is here, the eighteenth named storm of this remarkably active 2010 Atlantic hurricane season. Shary's formation makes 2010 tied for 5th place with 1969 for most number of named storms in an Atlantic hurricane season. Only 2005 (28 named storms), 1933 (21 named storms), 1995 (19 named storms), and 1887 (19 named storms) had more named storms than 2010 has had. Atlantic hurricane records go back to 1851, though there were likely many missed named storms prior to the beginning of satellite coverage in the mid-1960s. Shary is going to be a weak and very short-lived storm, and Bermuda is the only land area that needs be concerned with the storm. A Tropical Storm Warning is posted for the island, and rain bands from the storm can be seen on Bermuda radar.

Potentially dangerous 91L approaching South America and Lesser Antilles
A very impressive tropical wave (Invest 91L), about 350 miles east-southeast of the southernmost Lesser Antilles Islands, is headed west-northwest towards the islands at 15 - 20 mph. In discussions I had with hurricane experts at NHC and NOAA's Hurricane Research Division yesterday, it was widely agreed that this system was unusually large and well-organized for this time of year--something one would expect to see in early September, but not late October. The historical Atlantic hurricane data base shows no cases where a tropical depression has formed so far south and east so late in the year. "Ominous" and "unprecedented" were a few of the adjectives I heard used to describe 91L, and this system has the potential to be a dangerous storm for the islands of the eastern and central Caribbean.


Figure 1. Morning satellite image of 91L.

91L is centered very far to the south, near 10°N latitude, and this close proximity to the Equator has slowed development. Also slowing development has been the system's very large size--it takes time to spin up such a large circulation. Aiding development has been low wind shear of 5 - 10 knots, warm ocean temperatures of 29°C, and a very moist atmosphere. A pass by the ASCAT satellite last night revealed a nearly closed circulation, and top winds of about 30 mph. Visible satellite loops do not show a clear surface circulation yet, though the storm has plenty of heavy thunderstorm activity that is increasing in organization, with several impressive low-level curved rain bands.

Forecast for 91L
91L will continue moving west-northwest at a decreasing forward speed through Monday, bringing very heavy rain tonight and Saturday to the northern coast of South America and most of the Lesser Antilles. The center of the storm will track very close the coast of South America this weekend, and it is likely that this will slow or halt development over the weekend. By Monday, the center of 91L may pull far enough away from South America that more substantial development can occur. However, steering currents are expected to substantially weaken in the eastern Caribbean beginning on Monday, as a strong trough of low pressure develops over the Eastern U.S., weakening the ridge of high pressure steering 91L. The trough may be strong enough to pull 91L to the north, resulting in a potential threat to Haiti, the Dominican Republic, Puerto Rico, and the Lesser Antilles Islands by Wednesday of next week. We do have several models--the HWRF and GFS--that develop 91L into a hurricane by Wednesday. Shear is predicted to remain low, 5 - 10 knots, for most of the next five days, and water temperatures are at near record highs, 29 - 29.5°C. There is the potential for 91L to reach hurricane status if passage over South America this weekend does not disrupt the storm sufficiently. An Air Force hurricane hunter aircraft is scheduled to investigate 91L at 2pm this afternoon to see if a tropical depression has formed.


Figure 2. Hurricane Specialist Dan Brown coordinates with the Bermuda Weather Service, alerting them to the possibility that 92L might be upgraded to Tropical Storm Shary, necessitating issuance of a Tropical Storm Watch for the island that evening.

A Thursday evening shift at NHC
I spent another shift yesterday evening at the National Hurricane Center, where I've spent the week as a participant in their visiting scientist program. Each week during hurricane season, NHC invites a hurricane researcher or forecaster in academia, government, or private industry to spend a week shadowing the NHC forecasters as they prepare their forecast products. The evening shift is chosen, since it is less of a zoo, and the presence of the visiting scientist will present less of a distraction to the forecasters.

Once again, I spent the first portion of the shift working with Tropical Analysis and Forecasting Branch (TAFB) forecaster Wally Barnes, who made the intensity and position estimates of 90L, 91L, and 92L based on infrared satellite imagery. This task was accomplished using the Dvorak technique, a system of classifying cloud patterns of tropical cyclones based on how cold the cloud tops are, how much spiral banding is present, and other factors. We classified 92L (later to be Shary) as an ST2.5--a subtropical storm with 40 mph winds. The more dangerous tropical wave Invest 91L approaching the coast of South America got a far weaker classification, since the tops of its thunderstorms were not very cold, and the bands of clouds were fairly fragmented.

We presented our data to Senior Hurricane Specialist Dan Brown, who would be responsible for the decision whether or not to upgrade 92L to Shary. He was impressed with the ST2.5 classification we'd come up with for 92L, but wanted more evidence that the storm was as strong as this satellite estimate indicated. At 9:10pm, we had our evidence. The latest wind observations from NOAA buoy 41049 showed 33.4 knots (38 mph) as 92L passed by. This wind speed is just at the boundary of tropical storm force winds--39 mph. However, since the buoy's anemometer is at an elevation of 5 meters, an adjustment upwards to the wind speed is necessary to correct the winds to the standard measurement height of ten meters, due to frictional slowing of the wind near the surface. Thus, the buoy winds were more like 40 mph, above tropical storm force, and this was Tropical Storm Shary--if a closed circulation existed. Dan told us he was going to start writing an advisory package, in case additional data came in indicating 92L had a closed surface circulation. He called the Bermuda Weather Service to alert them that he was considering naming this system Shary, and that a tropical storm watch or warning might be required for the island that evening. Dan also called the head of the hurricane forecasting branch of NHC, James Franklin, to alert him of the impending new storm.


Figure 3. "This is the part where the world finds out about Shary," Hurricane Specialist Dan Brown told me as he filled out this form on his computer. About an hour before the first package of official advisories on a new tropical depression or tropical storm are sent out, NHC renumbers an Invest with the "AL" prefix and a number indicating how many tropical storms or depressions have occurred so far this year. In this case, 92L got renumbered AL20, since there have been 18 named storms and 2 tropical depressions that did not reach tropical storm strength. The newly numbered storm appears on the Navy Research Lab web site about an hour before the first advisory is sent out to the world. It is rare for NHC to change their mind and not issue advisories after renumbering occurs.

At 9:20pm, we had our proof of a closed circulation. A ship heading towards the center of Shary from the south measured west winds of 15 knots just south of the center, strongly suggesting that Shary had a closed circulation and was a legitimate tropical storm. Dan accelerated his work on the 11pm advisory package--there was a lot of work to do between now (9:30) and 10:30, when he wanted to get the advisories out. The other hurricane specialist on duty, Robbie Berg, helped out, and the two of them worked hard over the next hour to plot positions, scan the latest observations and model data, and type up advisories. Sandwiched between these efforts were several phone calls--a coordination call with other branches of NOAA and the Navy, another call to the Bermuda Weather Service, plus a conversation with Trinidad's weather service, which was concerned about the tropical wave (Invest 91L) approaching their island. Finally, at 10:30pm, the advisory package was complete, and Dan hit the "Send out to the Whole World?" button on his screen, making Tropical Storm Shary the eighteenth named storm of the 2010 Atlantic hurricane season.


Figure 4. Hurricane Specialist Robbie Berg updates NHC's big hurricane tracking board with its newest addition, Tropical Storm Shary.

It's worth noting that we would not have known Shary was a tropical storm without data from the buoy the storm passed over. This buoy was one of the new buoys financed by a special supplemental funding bill approved by Congress several years ago, in an effort to improve hurricane forecasts. Money well spent in this case!

Next update
I'll have an update later today or Saturday morning on the latest from the tropics.

Jeff Masters

Hurricane

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An evening shift at NHC: A Shary situation

By: JeffMasters, 2:57 PM GMT on October 28, 2010

We have a rare late October triple threat in the Atlantic this morning, three "Invests" with a decent chance of developing. The most serious threat is Invest 91L, a tropical wave centered near 7N 49W, about 950 miles east-southeast of the Lesser Antilles Islands. 91L is moving west to west-northwest at 15 - 20 mph, and will spread heavy rains and gusty winds to the northern coast of South America and the southern Lesser Antilles Islands beginning on Friday night. The system is under low wind shear less than 10 knots, but is too close to the Equator to spin up very rapidly. The storm will also have difficultly developing due to land interaction with South America this weekend. However, several models are indicating the possibility that 91L could develop into a tropical depression in the Central Caribbean by the middle of next week. NHC is giving 90L a 20% chance of developing into a tropical cyclone by Saturday.

A low pressure system (Invest 90L) centered near 27N 42W in the middle Atlantic Ocean has developed a broad and elongated circulation. Heavy thunderstorms on its east side are generating tropical storm-force winds. However, the circulation of 90L has become increasingly stretched out this morning, and the storm is not as well organized as it was last night. NHC is giving 90L a 50% chance of developing into a tropical storm by Saturday.

Finally, a low pressure system (Invest 92L) centered 700 miles south-southeast of Bermuda is developing a surface circulation, and appears very close to tropical depression status. NHC is giving 92L a 60% chance of developing into a tropical cyclone by Saturday. The only land area that might be affected by 92L is Bermuda.


Figure 1. A rare late-October triple threat in the Atlantic: three areas of disturbed weather listed by NHC as areas of interest (Invests) worth running forecast models on. Image credit: National Hurricane Center.

A quiet Tuesday evening shift at NHC
Tuesday evening was a quiet shift at the National Hurricane Center, where I've spent the week as a participant in their visiting scientist program. Each week during hurricane season, NHC invites a hurricane researcher or forecaster in academia, government, or private industry to spend a week shadowing the NHC forecasters as they prepare their forecast products. The evening shift is chosen, since it is less of a zoo, and the presence of the visiting scientist will present less of a distraction to the forecasters.

There was only one area of interest (Invest 90L) on Tuesday. 90L was a disorganized low pressure system in the middle Atlantic that had gotten tangled up with an upper-level low pressure system that was bringing dry air and disruptive wind shear. I worked with senior hurricane specialist Dan Brown, who cheerfully analyzed 90L with me, but confided that this storm was barely worth keeping as an Invest. He lowered its chances of development to 10%, but did order one more run of the various forecast models, so I could see how that was done. He also pointed out two other systems he thought might turn into "Invests" worth watching later in the week, and noted in particular that the large tropical wave approaching South America was unusually vigorous for this time of year, and might be something to be concerned about if it managed to avoid South America and penetrate into the southern Caribbean.

Since there wasn't much else to see on the hurricane end of their operation, I spent the rest of the evening working with NHC's marine forecasting branch. The National Hurricane Center is responsible for preparing weather analysis charts and marine forecasts for the tropical Atlantic and Eastern Pacific, and I worked with meteorologist Felix Garcia of NHC's Tropical Analysis and Forecast Branch (TAFB). He prepared the 8pm Tropical Weather Discussion, and the 00Z tropical analysis chart. I'm highly envious of the software tools NHC has to prepare forecasts and make analysis charts! I want an NAWIPS and ATCF workstation like these guys have, which allows one to zoom, pan, overlay, and quickly change speeds of animations. I'm proud to say that I am responsible for a portion of the 1016 mb isobar on the 00Z tropical Atlantic surface analysis map for Tuesday night, which I drew using the fantastic map drawing software at NHC.

Wednesday evening: A Shary situation
Wednesday evening was a bit more interesting. Invest 90L had been joined by Invest 91L and Invest 92L, and odds for development of 90L had been bumped up to 30%. I spent the first portion of the shift working with TAFB forecaster Wally Barnes, who made the intensity and position estimates of the three invests based on infrared satellite imagery. This task is accomplished using the Dvorak technique, a system of classifying cloud patterns of tropical cyclones based on how cold the cloud tops are, how much spiral banding is present, and other factors. Wally let me determine where the center of 90L was at 00Z last night, and enter the fix into the official database. I am now forever responsible for a tiny piece of the 2010 Atlantic hurricane data base--an awesome responsibility! (It's my first addition to the cause since I sent in my final Hurricane Hunter VORTEX report from the eye of Hurricane Hugo on September 15, 1989, complaining about hitting 5.7 G's of acceleration.) We classified 90L as a T2.0, which is respectable, and meant the system might be on its way to status as Tropical Storm Shary. Wally had to do the analysis for the large, ill-defined tropical wave (Invest 91L), since his eye was much more highly trained to pick out subtle motions in the satellite animations that indicated where the most likely center of circulation might be trying to develop.


Figure 2. "My boat is right here!" Forecaster Wally Barnes of NHC's Tropical Analysis and Forecasting Branch (TAFB) shows where he suspects the center of rotation of Invest 91L might be at 00Z on October 28, 2010.

Wally and I printed out the fix information we'd come up with for 90L, and took it over to Dan Brown, who was working the evening shift again over at the hurricane side of NHC.

"What, you're giving this a T2.0?" Dan good-naturedly hassled us, as we presented the fix info. "You're just trying to get something going for Jeff here so he can see some advisories get issued." Wally defended our analysis, pointing out how the heavy thunderstorms of 90L were pushing closer to the center of circulation, and how the cloud tops had gotten much colder. Dan agreed that 90L really was worthy of more attention, and commented that there was a good chance one of our three invests would probably develop into something NHC would have to issue advisories on before my final shift at NHC ended on Friday night. His prediction was that it would be 92L, the system a few hundred miles north of Puerto Rico.

An hour later, Dan wasn't so sure that 90L wouldn't beat 92L to the title of Tropical Storm Shary. The European ASCAT satellite had just sent in an image of the surface winds over 90L, and ASCAT was showing that the storm had a closed circulation and a respectable area of 40 mph tropical storm-force winds. He gave a call to James Franklin, the head of the hurricane specialist unit at NHC, who was at home. I listened in.

"Hey, I just got ASCAT," said Dan. "It's 35 knots. You can see the center, and the convection is about 130 miles to the northeast. I'm thinking of starting it as a tropical storm, but I hate to start it now, since the convection started at 21Z, and I'd like to see it persist. The ASCAT pass shows the circulation is a bit elongated, and the most recent microwave images are also showing that."

After discussing whether or not to initiate advisories on Tropical Storm Shary for a few more minutes, Dan hung up, then told me the scoop. "This is one of the most difficult parts of the job. It's a real judgment call whether or not to name a storm, when it's such a borderline situation like this. What we're going to do is issue a Special Tropical Weather Outlook mentioning that 90L has gale-force winds, bump the probability of development up to 50 or 60%, watch it for a few more hours, then re-assess." Dan then proceeded to call his replacement, Eric Blake, who was due to work the night shift, to tell him to come in as planned, since it looked like there could well be a Tropical Storm Shary to deal with. Dan then proceeded to write the Special Tropical Weather Outlook and send it out.


Figure 3. "The one that got away was this big!" Wally Barnes tells hurricane specialist Dan Brown what he thinks of 90L's recent burst of heavy thunderstorm activity.

Next update
I'll have an update on Thursday morning from the National Hurricane Center on the latest from the tropics.

Jeff Masters

Hurricane

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Strongest storm ever recorded in the Midwest smashes all-time pressure records

By: JeffMasters, 3:09 PM GMT on October 27, 2010

Tornadoes, violent thunderstorms, and torrential rains swept through a large portion of the nation's midsection yesterday, thanks to the strongest storm ever recorded in the Midwest. NOAA's Storm Prediction Center logged 24 tornado reports and 282 reports of damaging high winds from yesterday's spectacular storm, and the storm continues to produce a wide variety of wild weather, with tornado watches posted for Mississippi, Alabama, and Georgia, a blizzard warning for North Dakota, high wind warnings for most of the upper Midwest, and near-hurricane force winds on Lake Superior.

The mega-storm reached peak intensity late yesterday afternoon over Minnesota, resulting in the lowest barometric pressure readings ever recorded in the continental United States, except for from hurricanes and nor'easters affecting the Atlantic seaboard. So far, it appears the lowest reading (now official) was a pressure of 28.21" (955.2 mb) reduced to sea level reported from Bigfork, Minnesota at 5:13pm CDT. Other extreme low pressures from Minnesota during yesterday's storm included 28.22" (956 mb) at Orr at 5:34pm CDT, 28.23" at International Falls (3:45pm), and 28.23" at Waskuh at 5:52pm. The 28.23" (956mb) reading from International Falls yesterday obliterated their previous record of 28.70" set on Nov. 11, 1949 by nearly one-half inch of mercury--a truly amazing anomaly. Duluth's 28.36" (961 mb) reading smashed their old record of 28.48" (964 mb) set on Nov. 11, 1998. Wisconsin also recorded its lowest barometric pressure in history yesterday, with a 28.36" (961 mb) reading at Superior. The old record was 28.45" (963.4 mb) at Green Bay on April 3, 1982. The previous state record for Minnesota was 28.43" (963 mb) at Albert Lea and Austin on Nov. 10, 1998.


Figure 1. Visible satellite image of the October 26, 2010 superstorm taken at 5:32pm EDT. At the time, Bigfork, Minnesota was reporting the lowest pressure ever recorded in a U.S. non-coastal storm, 955 mb. Image credit: NASA/GSFC.

Yesterday's records in context
Yesterday's 28.21" (955 mb) low pressure reading in Minnesota breaks not only the 28.28" (958 mb) previous "USA-interior-of-the-continent-record" from Cleveland, Ohio during the Great Ohio Storm of Jan. 26, 1978 (a lower reading in Canada during this event bottomed out at an amazing 28.05"/950 mb), but also the lowest pressure ever measured anywhere in the continental United States aside from the Atlantic Coast. The modern Pacific Coast record is 28.40" (962mb) at Quillayute, Washington on Dec. 1, 1987. An older reading, taken on a ship offshore from the mouth of the Umpqua River in Oregon during the famous "Storm King" event on January 9, 1880, was 28.20" (954.9 mb)--slightly lower than the 2010 storm.

The lowest non-hurricane barometric pressure reading in the lower 48 states is 28.10" (952 mb) measured at Bridgehampton, New York (Long Island) during an amazing nor'easter on March 1, 1914 (see Kocin and Uccellini, "Northeast Snowstorms; Vol. 2., p. 324, American Meteorological Society, 2004.) The lowest non-hurricane barometric pressure reading from anywhere in the United States was a 27.35" (927 mb) reading at Dutch Harbor, Alaska on Oct. 25, 1977. The lowest hurricane pressure reading was the 26.34" (892 mb) recorded in 1935 during the Great Labor Day Hurricane.


Figure 2. Storm reports received by NOAA's Storm Prediction Center from the October 26, 2010 superstorm.

The six most intense storms in history to affect the Great Lakes
According to the Chicago branch of the National Weather Service and Christopher C. Burt, our Weather Records blogger, the following are the six lowest pressures measured in the U.S. Great Lakes region:

1. Yesterday's October 26, 2010 Superstorm (955 mb/28.20")
2. Great Ohio Blizzard January 26, 1978 (958 mb/28.28")
3. Armistice Day Storm November 11, 1940 (967 mb/28.55")
4. November 10, 1998 storm (967 mb/ 28.55")
5. White Hurricane of November 7 - 9, 1913 (968 mb/28.60")
6. Edmund Fitzgerald Storm of November 10, 1975 (980 mb/28.95")

So, the famed storm that sank the ore carrier Edmund Fitzgerald in 1974, killing all 29 sailors aboard, was weaker than the current storm. Indeed, I wouldn't want to be on a boat in Lake Superior today--sustained winds at the Rock of Ages lighthouse on Isle Royale were a sustained 68 mph, gusting to 78 mph at 3am EDT this morning!

Yet Another Remarkable Mid-latitude Cyclone so far this Year!
Yesterday's superstorm is reminiscent of the amazing low pressures reached earlier this year (Jan. 19-22) in the West, where virtually every site in California, Nevada, Utah, Arizona, southern Oregon, and southern Idaho--about 10 - 15% of the U.S. land area--broke their lowest on record pressure readings. However, the lowest readings from that event fell well short of yesterday's mega-storm with 28.85" (977 mb) being about the lowest recorded at any onshore site.

Commentary
We've now had two remarkable extratropical storms this year in the U.S. that have smashed all-time low pressure records across a large portion of the country. Is this a sign that these type of storms may be getting stronger? Well, there is evidence that wintertime extratropical storms have grown in intensity in the Pacific, Arctic, and Great Lakes in recent decades. I discuss the science in detail in a post I did earlier this year. Here is an excerpt from that post:

General Circulation Models (GCMs) like the ones used in the 2007 IPCC Assessment Report do a very good job simulating how winter storms behave in the current climate, and we can run simulations of the atmosphere with extra greenhouse gases to see how winter storms will behave in the future. The results are very interesting. Global warming is expected to warm the poles more than the equatorial regions. This reduces the difference in temperature between the pole and Equator. Since winter storms form in response to the atmosphere's need to transport heat from the Equator to the poles, this reduced temperature difference reduces the need for winter storms, and thus the models predict fewer storms will form. However, since a warmer world increases the amount of evaporation from the surface and puts more moisture in the air, these future storms drop more precipitation. During the process of creating that precipitation, the water vapor in the storm must condense into liquid or frozen water, liberating "latent heat"--the extra heat that was originally added to the water vapor to evaporate it in the first place. This latent heat intensifies the winter storm, lowering the central pressure and making the winds increase. So, the modeling studies predict a future with fewer total winter storms, but a greater number of intense storms. These intense storms will have more lift, and will thus tend to drop more precipitation--including snow, when we get areas of strong lift in the -15°C preferred snowflake formation region.

Invest 90L
A low pressure system (Invest 90L) in the middle Atlantic Ocean has developed a broad circulation, but has very limited heavy thunderstorm activity. NHC is giving 90L a 10% of developing into a tropical depression by Friday. Another area of disturbed weather a few hundred miles west of 90L is disorganized, and is also being given a 10% chance of developing.

Next update
I'll have an update on Thursday morning. I'm at the National Hurricane Center in Miami this week, as part of their visiting scientist program, and hopefully the weather in the rest of the country will slow down enough so I can write about goings-on here at the Hurricane Center!

Christopher C. Burt is responsible for most of the content of this post, with the exception of the commentary, which I wrote.

Jeff Masters

Climate Change

Updated: 5:02 PM GMT on November 18, 2010

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Tornadoes, violent thunderstorms rip the U.S.; Richard dies in the Gulf of Mexico

By: JeffMasters, 3:23 PM GMT on October 26, 2010

Tornadoes, violent thunderstorms, and torrential rains are sweeping through the nation's midsection today, thanks to an explosively deepening low pressure system over Minnesota. The spectacular storm is expected to bottom out at a central pressure of 960 mb later today, the type of central pressure one commonly encounters in Category 2 hurricanes. A powerful cold front trails southwards from the storm, and this cold front has spawned an impressive squall line studded with violent thunderstorms. As many as eleven simultaneous tornado warnings have been issued late this morning for these thunderstorms, from southern Michigan to northern Mississippi. So far, the tornadoes have been embedded within the squall line, and these type of tornadoes are typically weaker EF-0 to EF-1 twisters. However, as the day progresses and the sun's heating adds energy to the atmosphere, strong EF-2 or EF-3 tornadoes are likely, if discrete supercell thunderstorms separate from the squall line and begin to evolve. So far, six reports of tornadoes touching down have been received, but only minor damage has been reported. NOAA's Storm Prediction Center has placed much of southern Michigan, eastern Indiana, and western Ohio in their "High Risk" area for severe weather. "High Risk" days occur less than five times per year, on average, and are unusual in the fall. Fall storms this intense only occur perhaps once every 5 - 10 years. You can follow today's severe weather outbreak using our Severe Weather Page and Tornado page.


Figure 1. This morning's severe weather outlook from NOAA's Storm Prediction Center puts most of Indiana and Western Ohio into their highest category for severe weather.

Richard dies
Tropical Depression Richard emerged into the Gulf of Mexico this morning after crossing the Yucatan Peninsula. However, passage over the Yucatan so weakened the storm that it has officially been declared dead by NHC. There was too much dry air and wind shear in the Gulf of Mexico to allow Richard to regenerate. Richard hit central Belize Sunday night as a Category 1 hurricane with 90 mph winds. The storm is being blamed for $18 million in damage, but no deaths were reported. Belize lost about 1/3 of its orange crop to Richard's high winds. Electrical power is still out to 30% of the country, but is expected to be fully restored by tonight.


Figure 2. Visible MODIS satellite image of Hurricane Richard taken at 4:35pm EDT 10/25/10 by NASA's Aqua satellite. At the time, Richard was a tropical depression with 35 mph winds. Image credit: NASA.

Invest 90L
A low pressure system (Invest 90L) in the middle Atlantic Ocean has developed a broad circulation, with a band of heavy thunderstorms in an arc to the north and east of the storm. This hybrid subtropical system is under a moderate 10 - 20 knots of wind shear. Water temperatures are marginal for development, just 26.5 - 27°C (26.5°C is usually the limiting SST that a tropical storm can develop at.) NHC is giving 90L a 30% of developing into a subtropical depression or storm by Thursday.

Next update
I'll have an update on Wednesday morning. I'm at the National Hurricane Center in Miami this week, as part of their visiting scientist program, and will be shadowing NHC forecasters on the evening shift Tuesday - Friday to learn more about their operations. I'll probably talk tomorrow about the severe weather outbreak, but later this week I'll talk about what a shift at the Hurricane Center is like. I also have meetings planned with scientists at NOAA's Hurricane Research Division later this week, and plan to write about some of the research missions performed during this year's hurricane season.

Jeff Masters

Tornado Hurricane

Updated: 3:45 AM GMT on October 27, 2010

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Richard hits Belize, weakens to a tropical storm

By: JeffMasters, 12:38 PM GMT on October 25, 2010

Hurricane Richard hit central Belize last night at approximately 8:45pm EDT as a Category 1 hurricane with 90 mph winds. The hurricane made landfall about 20 miles south of Belize's largest city, Belize City (population approximately 100,000--1/3 of Belize's population.) Richard's northern eyewall passed just south of the airport, which measured top winds of 37 mph, gusting to 62mph, at 8pm CST. The airport picked up 3.66" of rain. Richard was a small hurricane, and hurricane-force winds affected a region of coast of no more than 20 - 30 miles wide, just to the south of Belize City. As Richard made landfall, the eye grew tighter and more defined, subjecting a smaller portion of the country to the extreme winds of the eyewall. This contraction of the eye was probably caused by frictional convergence--as the winds spiraling into the center of Richard passed from ocean to land, the increased friction caused the winds to slow down as they reached the eyewall. This made the inflowing air pile up near the eyewall, and this piled-up air was forced upwards into more violent updrafts, intensifying the thunderstorms in the eyewall and causing eye to contract. This intensification lasted only an hour or two, before the inland motion of the center removed Richard from its main energy source, the warm waters of the Western Caribbean.


Figure 1. Visible MODIS satellite image of Hurricane Richard taken at 12:45pm EDT 10/24/10 by NASA's Aqua satellite. A the time, Richard was a Category 1 hurricane with 85 mph winds. Image credit: NASA.

The top winds measured at any station in Belize occurred at a personal weather station on the offshore island of Caya Caulker, which had sustained winds of 54 mph yesterday afternoon at 3:55pm CST local time. Despite the relatively small portion of Belize that was subjected to strong winds from Richard, the storm was able to knock out power to the entire nation for a period of many hours. There are no reports of deaths or injuries, but preliminary media reports indicate major wind and flooding damage in regions near where the center came ashore.

Richard was a hurricane for 18 hours, and was the 10th hurricane of the 2010 Atlantic hurricane season. This year's ten hurricanes ties it for sixth place for most hurricanes in an Atlantic hurricane season. Our seventeen named storms this year also ranks as the 6th most in history. Atlantic hurricane season records go back to 1851.


Figure 2. Zoom radar image of Hurricane Richard at landfall, 8:53pm EDT 10/24/10. Belize City was just north of the northern eyewall, and did not receive tropical storm force winds, according to the hourly observations taken at the airport. However, Belmopan, the capital of Belize, experienced the northern eyewall of Richard. Image credit: Belize Meteorological Service.

Forecast for Richard
Richard has weakened to a tropical storm with 45 mph winds, as it moves west-northwest over the Yucatan Peninsula. Richard's small size and relatively slow forward speed of 5 - 10 mph will lead to continued weakening today as it crosses the Yucatan Peninsula. The storm will probably be a tropical depression when it emerges over the Gulf of Mexico on Tuesday--if it survives the crossing. If Richard does survive the crossing, moderate wind shear and dry air over the southern Gulf of Mexico should keep the storm from intensifying. Richard should dissipate by Wednesday, before affecting any other land areas.

Invest 90L
A low pressure system (Invest 90L) centered near 23N 42W in the middle Atlantic Ocean, has developed a broad circulation. A band of heavy thunderstorms has developed in an arc to the north and east of the storm, well removed from the center, suggesting that 90L is a hybrid subtropical system. Wind shear is a high 20 - 25 knots, but is predicted to drop to the moderate range, 10 - 20 knots, this afternoon through Wednesday. This may give 90L the opportunity to develop, though water temperatures are marginal for development, just 26.5 - 27°C (26.5°C is usually the limiting SST that a tropical storm can develop at.) The NOGAPS model is calling for 90L to develop into a depression by Friday, when the storm will be near Bermuda. NHC is giving 90L a 10% of developing into a tropical depression by Wednesday.

Next update
I'll have an update on Tuesday. I'm not sure when that update will be, as I am catching a flight to Miami in the morning. I've been invited to spend the week at the National Hurricane Center as part of their visiting scientist program, and will be shadowing NHC forecasters on the evening shift Tuesday - Friday to learn more about their operations. I'll be writing a post later this week about what a shift is like at the Hurricane Center. I also have meetings planned with scientists at NOAA's Hurricane Research Division, and plan to write about some of the research missions performed during this year's hurricane season.

Our weather extremes expert Christopher C. Burt has a very interesting post today on the hottest temperatures ever measured on Earth.

Jeff Masters

Hurricane

Updated: 12:39 PM GMT on October 25, 2010

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Hurricane Richard bears down on Belize

By: JeffMasters, 3:35 PM GMT on October 24, 2010

Data from an Air Force hurricane hunter aircraft confirms that Richard has intensified to hurricane strength, as it bears down on the coast of Belize. At 7:30am CST, the aircraft measured surface winds of 85 mph. Winds at their 5,000 foot flight level were 97 mph, qualifying Richard as the 10th hurricane of the 2010 Atlantic hurricane season. This year is now tied for sixth place for most hurricanes in an Atlantic hurricane season. This year's 17 named storms also ranks 6th most in history. Atlantic hurricane season records go back to 1851. Richard's center passed just north of the Honduras' Bay Islands this morning, bringing winds of 46 mph, gusting to 58 mph, to the Roatan Airport. Winds were clocked at 49 mph, gusting to 69 mph, at Calabash Bight on Roatan Island.

The latest 8am CST eye report from the Hurricane Hunters noted that Richard had formed a nearly complete eyewall, with a gap in the southwest side. Radar images from the Belize radar also showed this gap, but the gap closed at 9am CST, and Richard now has a complete eyewall, which will promote more rapid intensification. Recent satellite imagery shows a symmetrical, well-organized hurricane with respectable low level spiral banding, and upper level outflow improving in all quadrants. Richard has now walled itself off from the dry air to the storm's west, as seen on water vapor satellite loops.


Figure 1. The eye of Richard is very prominent in this radar image from the Belize radar taken at 9:15am CST 10/24/10. Image credit: Belize Meteorological Service.

Forecast for Richard
The latest set of 12am CST (6Z) model runs are in excellent agreement with Richard's track, taking the enter of the storm inland over Belize between 4pm - 9pm CST tonight. The latest radar animations from the Belize radar indicate that Belize City will experience a portion of the eyewall of Richard, and residents of Belize City can expect a 2 - 4 hour period of hurricane force winds to begin between 4pm - 6pm CST this evening. Tropical storm force winds of 39+ mph should arrive at the coast between 2pm - 4pm CST this afternoon. A good way to estimate these arrival times is using the wundermap with the "hurricane" layer turned on and the "wind radius" and "forecast" boxes checked. Richard is in a very favorable environment for intensification, with low wind shear between 5 - 10 knots, and warm water temperatures of 29 - 29.5°C. Given these conditions, and the fact that the eyewall is is now fully formed, Richard will probably undergo a period of rapid intensification that could take it to Category 2 strength with 100 mph winds at landfall this evening. Once inland, Richard's small size and relatively slow forward speed of 5 - 10 mph on Monday will lead to substantial weakening as it crosses the Yucatan Peninsula. The storm will probably be a tropical depression when it emerges over the Gulf of Mexico on Tuesday--if it survives the crossing. If Richard does survive the crossing, high wind shear over the Gulf of Mexico on Tuesday and Wednesday should keep the storm from intensifying. Richard should dissipate by Wednesday, before affecting any other land areas.

Invest 90L
A tropical wave (Invest 90L) centered 600 miles northwest of the Cape Verde Islands off the coast of Africa is encountering a very high 40 - 60 knots of wind shear. The shear is predicted to drop to the moderate range, 10 - 20 knots, Monday through Wednesday. This may give 90L the opportunity to develop, and the NOGAPS model is calling for 90L to develop into a tropical depression by mid-week. NHC is giving 90L a 10% of developing into a tropical depression by Tuesday.

Next update
I'll have an update on Monday morning at the latest.

Our weather extremes expert Christopher C. Burt has a very interesting post today on the hottest temperatures ever measured on Earth.

Jeff Masters

Hurricane

Updated: 3:36 PM GMT on October 24, 2010

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Richard intensifies; Megi hits China; no news from Myanmar on Giri's impact

By: JeffMasters, 4:14 PM GMT on October 23, 2010

Tropical Storm Richard suddenly overcame its struggles with dry air and wind shear this morning, took advantage of low wind shear of 5 - 10 knots and warm water temperatures of 29°C, and intensified into a strong tropical storm. An Air Force hurricane hunter aircraft departed Richard late this morning, and found that the storm had managed to develop respectable surface winds of 65 mph. However, they reported no sign of an eyewall forming, and additional intensification will be limited until Richard can develop an eyewall. Recent satellite imagery shows that Richard has a Central Dense Overcast (CDO) of high cirrus clouds expanding and covering the center of circulation, a telltale sign of an intensifying tropical storm. Low-level spiral bands are becomign more prominent, and upper-level outflow is improving on all sides except the west. Water vapor satellite loops show considerable dry air to the west of Richard, and this dry air is still causing some trouble for the storm. The next hurricane hunter aircraft is due in the storm near 8pm EDT tonight.


Figure 1. Forecast radius of tropical storm force winds of 39+ mph (dark green colors), winds of 58+ mph (light green colors) and hurricane force winds of 74+ mph (yellow colors) as predicted by NHC at 11am EDT 10/23/10. Hurricane force winds are predicted to affect just a small region to the northeast of Richard's center, beginning Sunday morning.

Forecast for Richard
The latest set of 2am EDT (6Z) model runs are similar to the previous set of runs. Richard will continue to move just north of west today, in response to a ridge of high pressure that is expected to build in over the Caribbean. This path will bring the center of Richard very close to Guanaja and Roatan Islands off the northern coast of Honduras near 8am EDT Sunday. Residents of those islands can expect tropical storm force winds of 39+ mph to arrive at the islands between 8 pm - midnight EDT tonight. A good way to estimate these arrival times is using the wundermap with the "hurricane" layer turned on and the "wind radius" and "forecast" boxes checked. The coast of Belize can expect tropical storm force winds of 39+ mph to arrive Sunday afternoon, between noon - 4pm EDT. The 11am EDT NHC wind probability forecast is giving the highest odds for tropical storm-force winds at Guanaja in Honduras, at 89%. Belize City is next highest, at 69%. Richard will pass very close to the coast of northern Honduras today, which may limit intensification some. Dry air to the west may also be a problem for the storm, and it is unlikely that Richard will grow stronger than a Category 2 hurricane with 100 mph winds. NHC is currently giving Richard a 4% chance of intensifying into a Category 3 or stronger hurricane before making landfall in Belize on Sunday. The models predict that Richard will dissipate over the Yucatan Peninsula on Monday. If the storm does make it to the Gulf of Mexico, Richard will probably dissipate by Tuesday or Wednesday, due to high wind shear, and the storm is not a threat to the U.S.

Invest 90L
A tropical wave (Invest 90L) centered near the Cape Verde Islands off the coast of Africa is encountering 30 knots of wind shear. The shear is predicted to rise over the few days, discouraging further development. NHC is giving 90L a 20% of developing into a tropical depression by Monday.

No news yet on Cyclone Giri's impact on Myanmar
Powerful Cyclone Giri made landfall Friday morning on the coast of Myanmar (Burma) as an upper-end Category 4 storm with 155 mph winds. Giri strengthened from a 60 mph tropical storm at to a 155 mph Category 4 storm in just 24 hours, leaving little time to evacuate the coastal regions in its path. Giri's winds at landfall were 20 mph stronger than those of Cyclone Nargis of 2008, which killed over 138,000 people. However, Giri hit a portion of the Myanmar coast that is not as heavily populated or as low-lying, so this will not be another Nargis catastrophe. Nevertheless, Giri's record strength and remarkably rapid intensification rate undoubtedly surprised an unprepared population, and the potential exists for a significant death toll. Communications with the disaster area are out, and the impacts of the storm are unknown at this time.

Typhoon Megi hits China
Typhoon Megi made landfall on the coast of China opposite from Taiwan near noon local time on Saturday afternoon. Megi was a Category 1 typhoon with 80 mph winds at landfall, and brougt torrential rains to both China and Taiwan. Mudslides and flooding from Megi's rains in Taiwan left 12 people dead and 26 missing, and the typhoon is also killed 36 people and left $176 million in damage earlier this week in the Philippines. The remnants of Megi are bringing only moderate amounts of rain to the coast of China this afternoon, and flooding damage may not be a great as previously feared.


Figure 2. Radar image of Typhoon Megi at 10:30am Taiwan time on Saturday, October 23, 2010, as Megi was making landfall on the coast of China opposite from Taiwan. Image credit: Taiwan Central Weather Bureau.

Next update
I'll have an update Sunday.

Our weather extremes expert Christopher C. Burt has a very interesting post today on the hottest temperatures ever measured on Earth.

Jeff Masters

Hurricane

Updated: 4:15 PM GMT on October 23, 2010

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Little change to Richard; Giri strongest cyclone ever to hit Myanmar; Megi nears China

By: JeffMasters, 9:07 PM GMT on October 22, 2010

Tropical Storm Richard continues to struggle with dry air and wind shear, despite the fact that both of these influences have waned significantly today. However, the storm is poised to begin a period of steady intensification that should take it to hurricane strength by Sunday. There have not been any hurricane hunter aircraft in Richard since late this morning, and we have to wait until 8pm tonight for the next mission to arrive. The closest buoy to Richard is NOAA buoy 42057, which is about 80 miles north of the center. Winds at the buoy were 38 mph, gusting to 47 mph, at 3:43am EDT. Recent satellite imagery shows that Richard has not changed much in organization today. Water vapor satellite loops show considerable dry air to the west of Richard, and this dry air may cause some trouble for the storm over the next few days. The waters beneath Richard are very warm, 29°C.


Figure 1. Afternoon satellite image of Richard.

Intensity forecast for Richard
The latest SHIPS model forecast predicts that wind shear over the Western Caribbean will remain in the low range, 5 - 10 knots, Saturday through Monday. As the storm moves westwards on Saturday, it may draw close enough to coast of Honduras to hamper intensification. Assuming Richard avoids making landfall in Honduras, the light shear and warm waters that extend to great depth should allow Richard to intensify into a Category 1 hurricane by Sunday. The 5pm NHC wind probability forecast is giving Richard a 7% chance of becoming a major Category 3+ hurricane. I believe the odds are higher, near 20%. The main inhibiting factor for intensification will be interaction with the north coast of Honduras, and the possibility of the dry air to the west of Richard getting wrapped into the core of the storm while it is trying to organize. A band of very strong upper-level winds associated with the jet stream will be over the Gulf of Mexico early next week, so it is likely that if Richard crosses into the Gulf of Mexico, the storm will be unable to intensify once it passes north of the latitude of the Florida Keys.

Track forecast for Richard
The latest set of 8am EDT (12Z) model runs are similar to the previous set of runs. On Saturday, Richard will move west at an increasing rate of speed in response to a ridge of high pressure that is expected to build in over the Caribbean. This path will bring the center of Richard close to the northern coast of Honduras on Saturday and Sunday, resulting in very heavy rains of 3 - 7 inches along the coast. None of the models predict a more northwesterly path towards Cancun/Cozumel or the western tip of Cuba, and Florida is not at risk of Richard coming its way over the next five days. The 5pm EDT NHC wind probability forecast is giving the highest odds for tropical storm-force winds at Guanaja in Honduras, at 70%. Belize City is next highest, at 65%, and the odds are 31% for Cozumel. If Richard never reaches hurricane strength, it may dissipate over the Yucatan Peninsula, as predicted by the NOGAPS and ECMWF models. If Richard does intensify into a hurricane, as predicted by the GFDL model, the storm may survive crossing the Yucatan, and emerge into the Gulf of Mexico on Tuesday. Very high wind shear associated with the jet stream is expected to be over the Gulf of Mexico next week, so if Richard begins moving north or northeast towards the U.S. Gulf Coast, dissipation before landfall is to be expected.

Invest 90L
A tropical wave (Invest 90L) centered about 100 miles southwest of the Cape Verde Islands off the coast of Africa has a modest amount of spin and heavy thunderstorm activity. Wind shear is a moderate 10 - 20 knots, and the waters are warm enough to support tropical storm formation. NHC is giving the system a 40% chance of developing into a tropical depression by Sunday. By Sunday, 90L's northwest movement will take the storm into a region of high wind shear of 20 - 40 knots, discouraging further development. This system is not a threat to cross the Atlantic and affect the Lesser Antilles or North America.

Cyclone Giri hits Myanmar
Powerful Cyclone Giri made landfall this morning on the coast of Myanmar (Burma) as an upper-end Category 4 storm with 155 mph winds. Giri strengthened from a 60 mph tropical storm at 8am EDT yesterday to a 155 mph Category 4 storm by 8am this morning, becoming the strongest cyclone ever to hit Myanmar. Giri's winds at landfall were 20 mph stronger than those of Cyclone Nargis of 2008, which killed over 138,000 people. However, Giri hit a portion of the Myanmar coast that is not as heavily populated or as low-lying, so this will not be another Nargis catastrophe. Nevertheless, Giri's record strength and remarkably rapid intensification rate undoubtedly surprised an unprepared population, and the potential exists for a significant death toll due to Giri's surge and winds. Also of major concern is flooding from heavy rains. Giri is expected to dump 4 - 8 inches of rain along its path inland over Myanmar over the next 24 hours.


Figure 2. Visible MODIS satellite image of Tropical Cyclone Giri taken at 2:55am EDT October 22, 2010. At the time, Giri was a Category 4 storm with 145 mph winds. Image credit: NASA.

Typhoon Megi unleashes torrential rains on Taiwan and China
Torrential rains from Typhoon Megi have triggered flooding and landslides in Taiwan that have left 7 people dead and 23 missing. The typhoon is also being blamed for the deaths of 36 people and $176 million in damage earlier this week in the Philippines. Megi continues its slow march towards China at 5 mph, and is expected to make landfall Saturday afternoon on the Chinese coast opposite from Taiwan. Megi is a large and powerful Category 1 typhoon with 90 mph winds, but rising wind shear has significantly weakened the storm today. Megi will continue to weaken until landfall, but will still be capable of causing considerable wind and storm surge damage even at Category 1 strength. Heavy rain will likely cause serious flooding since Megi is moving slowly and is a huge storm. I expect Megi will be a billion-dollar disaster for China, mostly due to flooding from heavy rains. The outer rain bands of Megi will continue to affect Taiwan and the coast of China near Taiwan through Saturday, as seen on China's radar composite and Taiwan radar.


Figure 3. Radar image of Typhoon Megi at 4:30pm EDT (4:30am Taiwan time) on October 22, 2010. Image credit: Taiwan Central Weather Bureau.

Next update
I'll have an update Saturday.

Jeff Masters

Hurricane

Updated: 9:58 PM GMT on October 22, 2010

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Richard not strengthening yet; Category 4 Giri hits Myanmar; Megi approaching China

By: JeffMasters, 2:04 PM GMT on October 22, 2010

Tropical Storm Richard remains a minimal strength tropical storm this morning, but is poised to begin a period of steady intensification that should take it to hurricane strength by Sunday. Richard is the seventeenth named storm of this very busy 2010 Atlantic hurricane season, putting 2010 into 6th place for the greatest number of named storms in the Atlantic since record keeping began in 1851. Only 2005 (28 named storms), 1933 (21 named storms), 1995 (19 named storms), 1887 (19 named storms), and 1969 (18 named storms) had more.

An Air Force hurricane hunter aircraft is currently in Richard, but has not seen much change in the storm's winds. As of 9:45am EDT this morning, top winds at flight level of 1200 feet were 46 mph, and the top surface winds seen so far by their SFMR instrument were 49 mph. The closest buoy to Richard is NOAA buoy 42057, which is on Richard's weak side about 80 miles northwest of the center. Winds at the buoy were 34 mph, gusting to 43 mph, at 8:44am EDT. Recent satellite imagery shows that Richard has become more organized since last night, with a large Central Dense Overcast (CDO) of high cirrus clouds forming over the center. A CDO is created when strong thunderstorms near the center of a developing tropical storm create updrafts that shoot moisture high into the atmosphere. When the moisture hits the bottom of the stratosphere, the moisture condenses into cirrus clouds that flatten out and spread horizontally into the CDO, which is kind of like a giant version of the flat anvil top one sees at the top of mature thunderstorms. The low-level center of Richard is no longer nearly exposed to view, and heavy thunderstorms are now firing off near the center, a sign that wind shear has relaxed and serious intensification can progress. Richard has several curved spiral bands forming on the south and east sides, and upper level outflow is improving on all sides except the west. Satellite intensity estimates put Richard's strength at about 50 - 55 mph. Water vapor satellite loops show considerable dry air to the west of Richard, and this dry air may cause some trouble for the storm over the next few days. The waters beneath Richard are very warm, 29°C.


Figure 1. Total accumulated rainfall for Richard predicted by the 2am EDT (6Z) October 22, 2010 run of the GFDL model. The model expects top rains from Richard in the 4 - 8 inch rain (dark green colors) with a few isolated areas of 8+ inches. Image credit: Morris Bender, NOAA/GFDL.

Intensity forecast for Richard
The latest SHIPS model forecast predicts that wind shear over the Western Caribbean will remain in the low range, 5 - 10 knots, today through Tuesday. As the storm moves westwards on Saturday, it may draw close enough to coast of Honduras to hamper intensification. Assuming Richard avoids making landfall in Honduras, the light shear and warm waters that extend to great depth should allow Richard to intensify into a Category 1 hurricane by Sunday. The 5am NHC wind probability forecast is giving Richard a 4% chance of becoming a major Category 3+ hurricane. I believe the odds are higher, near 20%. The main inhibiting factor for intensification will be interaction with the north coast of Honduras, and the possibility of the dry air to the west of Richard getting wrapped into the core of the storm while it is trying to organize. A band of very strong upper-level winds associated with the jet stream will be over the Gulf of Mexico early next week, so it is likely that if Richard crosses into the Gulf of Mexico, the storm will be unable to intensify once it passes north of the latitude of the Florida Keys.

Track forecast for Richard
The latest set of 2am EDT (6Z) model runs are in much better agreement on the path of Richard compared to yesterday. Steering currents are weak in the Western Caribbean, and Richard will move little today. By Saturday, Richard will begin moving due west in response to a ridge of high pressure that is expected to build in over the Caribbean. This path will bring the center of Richard close to the northern coast of Honduras on Saturday and Sunday, resulting in very heavy rains of 3 - 7 inches along the coast. None of the models predict a more northwesterly path towards Cancun/Cozumel or the western tip of Cuba any longer, and Florida is not at risk of Richard coming its way over the next five days. The 5am EDT NHC wind probability forecast is giving the highest odds for tropical storm-force winds at Guanaja in Honduras, at 54%. Belize City is next highest, at 42%, and the odds have dropped to 28% for Cozumel. If Richard never reaches hurricane strength, it may dissipate over the Yucatan Peninsula, as predicted by the NOGAPS, GFS, and ECMWF models. If Richard does intensify into a hurricane, as predicted by the GFDL model, the storm may survive crossing the Yucatan, and emerge into the Gulf of Mexico on Tuesday. Very high wind shear associated with the jet stream is expected to be over the Gulf of Mexico next week, so if Richard begins moving north or northeast towards the U.S. Gulf Coast, steady weakening is to be expected.

Invest 90L
A tropical wave (Invest 90L) about 100 miles south of the Cape Verde Islands off the coast of Africa has a modest amount of spin and heavy thunderstorm activity. Wind shear is a moderate 10 - 20 knots, and the waters are warm enough to support tropical storm formation. NHC is giving the system a 30% chance of developing into a tropical depression by Sunday. By Sunday, 90L's northwest movement will take the storm into a region of high wind shear of 20 - 40 knots, discouraging further development. This system is not a threat to cross the Atlantic and affect the Lesser Antilles or North America.

Cyclone Giri hits Myanmar
Powerful Cyclone Giri is making landfall this morning on the coast of Myanmar (Burma) as a Category 4 storm with 145 mph winds. Giri is one of the strongest cyclones ever to hit Myanmar, and has winds 10 mph stronger than Cyclone Nargis of 2008, which killed over 138,000 people. However, Giri is hitting a portion of the Myanmar coast that is not low-lying, and the major threat from Giri will be wind damage and flooding from heavy rains. Giri put on an impressive rapid intensification burst over the past 18 hours, strengthening from a 60 mph tropical storm at 8am EDT yesterday to a 145 mph Category 4 storm by 2am this morning.


Figure 2. Visible MODIS satellite image of Tropical Cyclone Giri taken at 2:55am EDT October 22, 2010. At the time, Giri was a Category 4 storm with 145 mph winds. Image credit: NASA.

Typhoon Megi unleashes torrential rains on Taiwan and China
Torrential rains from Typhoon Megi have triggered flooding and landslides in Taiwan that have left 3 people dead and more than 20 missing. The typhoon is also being blamed for the deaths of 36 people and $176 million in damage earlier this week in the Philippines. Megi continues its slow march towards China at 5 mph, and is expected to make landfall Saturday morning on the Chinese coast opposite from Taiwan. Megi remains a large and powerful Category 2 typhoon with 110 mph winds today, but rising wind shear is beginning to erode the northern portion of the storm's eyewall. It likely that Megi's eyewall will collapse before landfall, resulting in substantial weakening to a Category 1 storm. Megi will still be a very large and powerful storm capable of causing considerable wind and storm surge damage even at Category 1 strength. Heavy rain will likely cause serious flooding since Megi is moving slowly and is a huge storm. I expect Megi will be a billion-dollar disaster for China, mostly due to flooding from heavy rains. The outer rain bands of Megi will affect Taiwan and the coast of China near Taiwan all day today, as seen on China's radar composite and Taiwan radar.


Figure 3. Radar image of Typhoon Megi at 8:20am EDT (20:20 Taiwan time) on October 22, 2010. Image credit: Taiwan Central Weather Bureau.

Next update
I'll have an update this afternoon.

Jeff Masters

Hurricane

Updated: 2:11 PM GMT on October 22, 2010

Permalink

Tropical Storm Richard slowly intensifying

By: JeffMasters, 7:31 PM GMT on October 21, 2010

Tropical Storm Richard is here, the seventeenth named storm of this very busy 2010 Atlantic hurricane season. Richard's formation puts 2010 in 6th place for the greatest number of named storms in the Atlantic since record keeping began in 1851. Only 2005 (28 named storms), 1933 (21 named storms), 1995 (19 named storms), 1887 (19 named storms), and 1969 (18 named storms) had more.

We won't have another hurricane hunter aircraft in Richard until 8pm tonight, so we will have to rely on satellite intensity estimates until then. The closest buoy to Richard is NOAA buoy 42057, which is on Richard's weak side about 100 miles from the heaviest thunderstorms. Winds at the buoy were just 18 mph, gusting to 22 mph, at 2:43pm EDT this afternoon. Recent satellite imagery shows that Richard is steadily organizing, with several curved spiral bands forming on the storm's south and east sides. The storm is bringing very heavy rain to Jamaica. Water vapor satellite loops show considerable dry air to the west and north of Richard, and the southwesterly upper-level winds over the storm are bringing some of this dry into the core of the storm, keeping all the heavy thunderstorm development confined to the east side of the center. The waters beneath Richard are very warm, 29°C, and Richard will begin taking advantage of these warm waters now that the shear is falling.


Figure 1. Afternoon satellite image of Richard.

Intensity forecast for Richard
The latest SHIPS model forecast predicts that wind shear over the Western Caribbean will remain in the low range, 5 - 10 knots, through Monday morning. As the storm moves westwards on Friday, it will position itself beneath an upper-level high pressure system, which will aid the storm's upper-level outflow. With water temperatures a very warm 29°C and warm waters extending to great depth, Richard should be able to attain at least Category 1 hurricane strength by Saturday. NHC is currently giving Richard a 11% chance of becoming a major Category 3+ hurricane. I believe the odds are higher, near 30%. The main inhibiting factor for intensification will be interaction with the north coast of Honduras, and the possibility of the dry air to the west of Richard getting wrapped into the core of the storm while it is trying to organize. A band of very strong upper-level winds associated with the jet stream will be over the Gulf of Mexico early next week, so it is likely that if Richard crosses into the Gulf of Mexico, the storm will steadily weaken.

Track forecast for Richard
The latest set of 8am EDT (12Z) model runs are similar to the previous set of runs, and don't help illuminate what the long-range fate of Richard might be. Steering currents are weak in the Western Caribbean, and will remain weak through Friday morning, resulting in a slow, erratic movement for Richard. Most of the models favor a southerly, then southwesterly path at 5mph or less over the next two days. This may bring the center of Richard very close to or over the northern coast of Honduras on Saturday or Sunday, as predicted by the GFS, UKMET, and NOGAPS models. These models then show Richard dissipating over Central America. A much different solution is offered by the ECMWF, HWRF and GFDL models, which foresee less of a southerly motion for Richard over the next two days, resulting in the storm missing the north coast of Honduras by one hundred miles or more. These models take Richard to the northwest across the tip of the Yucatan (GFDL and ECMWF models) or western tip of Cuba (HWRF model) on Sunday or Monday. The HWRF and GFDL models predict Richard will be a threat to the west coast of Florida on Tuesday. NHC takes the reasonable approach of predicting a path somewhere between these two extremes, with Richard crossing the Yucatan between Cozumel and the Belize/Mexico border. Residents of northern Honduras should anticipate the possibility that Richard will pass very close or strike Honduras on Saturday or Sunday. Very heavy rains of 4 - 8 inches are possible over the the weekend in coastal Honduras beginning Friday night or Saturday morning. The 11am EDT NHC wind probability forecast is giving the highest odds for tropical storm-force winds at Guanaja in Honduras, at 46%. Cozumel, Mexico is given a 42% chance, Key West a 6% chance, and Ft. Myers a 3% chance.

Invest 90L
A tropical wave that emerged off the coast of Africa yesterday (Invest 90L) has a modest amount of spin and some growing thunderstorm activity. Wind shear is a moderate 5 - 15 knots, and the waters are still warm enough to support tropical storm formation. NHC is giving the system a 30% chance of developing into a tropical depression by Saturday. By Sunday, 90L will encounter high wind shear of 20 - 40 knots, discouraging further development. This system is not a threat to cross the Atlantic and affect the Lesser Antilles or North America.

Typhoon Megi takes aim at China
Typhoon Megi continues it slow march towards China at 5 mph, and is expected to make landfall Saturday morning on the Chinese coast opposite from Taiwan. Megi has maintained strength as a Category 3 typhoon with 115 mph winds today, despite rising wind shear (now a moderate 10 - 20 knots) and cooling sea surface temperatures. Megi is moving slow enough and is large and powerful enough that it is probably upwelling cold water from the depths to the surface faster than it can move away, and these upwelling cool waters are keeping Megi from being a stronger storm. Wind shear will increase dramatically to 20 - 40 knots on Friday as the typhoon makes its final approach to the coast of China, and this shear should be high enough to reduce Megi to Category 1 status before landfall. Megi will still be a very large and powerful storm capable of causing considerable wind and storm surge damage even at Category 1 strength. However, heavy rain will likely be the storm's main threat, since it is moving slowly and is a huge storm. I expect Megi will be a billion-dollar disaster for China, mostly due to flooding from heavy rains. The outer rain bands of Megi are already affecting the coast of China near Taiwan, as seen on China's radar composite, as well as Taiwan radar.

The clean-up continues in the Philippines from Megi, which hit northern Luzon island on Monday morning at 3:30 UTC as a Category 5 super typhoon with sustained winds of 165 mph and a central pressure of 914 mb. Severe damage was done to Isabela Province in northern Luzon, and 19 deaths are being blamed on the storm. Considering most major typhoon that have hit the Philippine in recent year have killed hundreds and sometimes thousands of people, the low death toll from Megi is a testament to the excellent efforts by officials in the Philippines to get people out of harm's way in advance of the storm.


Figure 2. Rainfall rate for Megi as observed by the TRMM polar orbiting satellite at 10:01am EDT October 21, 2010. Heavy rains in excess of 0.8" per hour (yellow colors) were present in Megi's eyewall and spiral bands. Image credit: Navy Research Lab, Monterey.

Next update
I'll have an update Friday morning.

Jeff Masters

Hurricane

Updated: 7:33 PM GMT on October 21, 2010

Permalink

Tropical Storm Richard is likely later today

By: JeffMasters, 1:48 PM GMT on October 21, 2010

The Hurricane Hunters are in Tropical Depression Nineteen, and have found winds of tropical storm force that support upgrading the depression to Tropical Storm Richard. Between 8:15 - 8:30am EDT, the Air Force hurricane hunter aircraft measured surface winds of 40 - 70 mph with their SFMR instrument in the heavy thunderstorm region on the east side of TD 19's center. Winds at the aircraft's flight level of 1400 feet peaked at 46 mph. These measurements support upgrading TD 19 to at least a 40 mph tropical storm. Winds have been steadily rising this morning at NOAA buoy 42057, located about 50 miles west-southwest of the center of TD 19, on its weak side. Winds were 27 mph, gusting to 29 mph, at 7:43am EDT this morning. Recent satellite imagery shows that the surface circulation center of TD 19 is nearly exposed to view, thanks to moderate wind shear of 10 - 20 knots from upper-level southwesterly winds. TD 19 has a moderate and increasing amount of heavy thunderstorm activity which is getting more organized, with a curved spiral band forming on the storm's south side. The storm is bringing very heavy rain to Jamaica. Water vapor satellite loops show considerable dry air to the west and north of TD 19, and the southwesterly winds over the storm are bringing some of this dry into the core of the storm, keeping all the heavy thunderstorm development confined to the east side of the center. The waters beneath TD 19 are very warm, 29°C, but TD 19 will not be able to take full advantage of these warm waters until the shear relaxes and stops pushing dry air into the core.


Figure 1. Morning satellite image of TD 19.

Intensity forecast for TD 19
The latest SHIPS model forecast predicts that wind shear over the Western Caribbean will remain in the moderate range, 10 - 20 knots, through Friday morning. As the storm moves westwards on Friday, it will position itself beneath an upper-level high pressure system, which will allow shear to drop to the low range, less than 10 knots. With water temperatures a very warm 29°C and warm waters extending to great depth, TD 19 should be able to attain at least Category 1 hurricane strength by Saturday. NHC is currently giving TD 19 a 3% chance of becoming a major Category 3 hurricane. Given the latest data from the Hurricane Hunters and the latest set of computer models runs, I believe the odds are higher, near 30%. The main inhibiting factor for intensification will be the possibility of the dry air to the west of TD 19 getting wrapped into the core of the storm while it is trying to organize.

Track forecast for TD 19
Steering currents are weak in the Western Caribbean, and will remain weak through Friday morning, resulting in a slow, erratic movement for TD 19. A slow drift to the south is the most popular track expected by the major models. Thus, Jamaica can expect rains to increase and become torrential at times until Saturday, when the storm will finally move off. The Cayman Islands and possibly the north coast of Honduras can also expect very heavy rains of 3 - 6 inches Friday through Saturday. By Friday afternoon, a ridge of high pressure is expected to build in, forcing TD 19 to the west or west-northwest, bringing the storm to a landfall in Belize or Mexico's Yucatan Peninsula Sunday night. The models are divided on what might happen after Sunday, with the GFS, NOGAPS, and UKMET models indicating a continued west-northwest track taking TD 19 across the Yucatan Peninsula and into the Gulf of Mexico, where high wind shear would destroy the storm early next week before it could make landfall in the U.S. The other model solution, provided by the ECMWF, GFDL, and HWRF models, is for TD 19 to get caught up by a trough of low pressure moving across the Eastern U.S. early next week, which would take the storm to the northwest through the Yucatan Channel and into the west coast of Florida as early as Monday night. A band of very strong upper-level winds associated with the jet stream will be over the Gulf of Mexico early next week, so it is likely that if TD 19 follows this track, the storm will be weakening quickly as it approaches Florida. Either solution is possible, and we will have to wait to see what future model runs show will happen. The 5am EDT NHC wind probability forecast is giving the highest odds for tropical storm-force winds at Guanaja in Honduras and Cozumel in Mexico, at 34% and 37%, respectively. Key West is the only U.S. city being given odds, and these are just 3%. These odds will very likely rise with the 11am NHC advisory.

Invest 90L
A tropical wave that emerged off the coast of Africa yesterday (Invest 90L) has a modest amount of spin and some growing thunderstorm activity. NHC is giving the system a 10% chance of developing into a tropical depression by Saturday. This system is not a threat to cross the Atlantic and affect the Lesser Antilles or North America.

Typhoon Megi takes aim at China
Typhoon Megi continues it slow march towards China at 5 mph, and is expected to make landfall Saturday morning on the Chinese coast opposite from Taiwan. Megi has been gradually declining in strength as it heads north, due to steadily rising wind shear (now a moderate 10 - 20 knots) and cooling sea surface temperatures. Megi is moving slow enough and is large and powerful enough that it is probably upwelling cold water from the depths to the surface faster than it can move away, and these upwelling cool waters are keeping Megi from being a major Category 3 typhoon. Wind shear will increase dramatically to 20 - 40 knots on Friday as the typhoon makes its final approach to the coast of China, and this shear should be high enough to reduce Megi to Category 1 status before landfall. Megi will still be a very large and powerful storm capable of causing considerable wind and storm surge damage even at Category 1 strength. However, heavy rain will likely be the storm's main threat, since it is moving slowly and is a huge storm. I expect Megi will be a billion-dollar disaster for China, mostly due to flooding from heavy rains. The outer rain bands of Megi are already affecting the coast of China near Taiwan, as seen on China's radar composite, as well as Taiwan radar.

The clean-up continues in the Philippines from Megi, which hit northern Luzon island on Monday morning at 3:30 UTC as a Category 5 super typhoon with sustained winds of 165 mph and a central pressure of 914 mb. Severe damage was done to Isabela Province in northern Luzon, and 19 deaths are being blamed on the storm. Considering most major typhoon that have hit the Philippine in recent year have killed hundreds and sometimes thousands of people, the low death toll from Megi is a testament to the excellent efforts by officials in the Philippines to get people out of harm's way in advance of the storm.


Figure 2. Rainfall rate for Megi as observed by the F-17 polar orbiting satellite at 5:49am EDT October 21, 2010. Heavy rains in excess of one inch per hour (orange colors) were present on the south side of Megi's eye, and a region of heavy rain was also present in a spiral band approaching the coast of China opposite from Taiwan. Image credit: Navy Research Lab, Monterey.

Next update
I'll have an update this afternoon.

Jeff Masters

Hurricane

Permalink

Little change to 99L, which remains very close to tropical depression status

By: JeffMasters, 7:11 PM GMT on October 20, 2010

A tropical disturbance (Invest 99L) centered 160 miles southwest of the Cayman Islands is moving south to southeast at 5 - 10 mph. A Hurricane Hunter flight arrived in the storm at about 11am this morning, and found a closed circulation with top winds at flight level (700 feet) of 33 mph. A closed circulation and 30 mph surface winds are necessary conditions for a tropical depression to exist, but the storm must also have a great deal of heavy thunderstorm activity near the center that persists for many hours. In the judgment of NHC, 99L does not qualify as a tropical depression in that regard. The storm is bringing heavy rain to the Cayman Islands; 4.14" inches has fallen over the past 2 1/2 days at Savannah on Grand Cayman Island. Heavy rains have diminished over the Cayman Islands, but have spread to western Jamaica and west-central Cuba this afternoon. Recent satellite imagery shows that the surface circulation center is exposed to view, and 99L has a relatively meager amount of heavy thunderstorm activity. The center is more than 80 miles west of the heaviest thunderstorm activity, and it is likely that 99L's center will relocate itself to the east to be more underneath the heaviest thunderstorms. Wind shear is marginal for development, 15 - 20 knots, due to the clockwise flow of air around an upper-level high pressure system near the coast of Honduras. The high is bringing strong upper-level winds out of the southwest to 99L. Water vapor satellite loops show considerable dry air to the west and north of 99L, and the strong southwesterly winds over the storm are bringing some of this dry into into the core of the storm, keeping all the heavy thunderstorm development confined to the east side of the center. The waters beneath 99L are very warm, 29°C, but 99L will not be able to take advantage of these warm waters until the shear relaxes. A new hurricane hunter aircraft will be in the storm tonight near 8pm EDT.

Forecast for 99L
The current southward movement of 99L is carrying the storm into a region of lower wind shear, and we should see 99L accumulate more heavy thunderstorm activity near its center beginning tonight. The latest SHIPS model forecast predicts that wind shear over the Western Caribbean will decline below 15 knots Thursday afternoon through Saturday afternoon, which should allow the storm to become a tropical depression by Thursday. Steering currents will be weak today through Friday in the Western Caribbean, making it difficult to predict where 99L may go. The models are split into two camps, with the GFDL and HWRF models taking 99L to the west-northwest over the western tip of Cuba or the Yucatan Peninsula on Sunday as a hurricane. The rest of the models take 99L to the south over Honduras on Sunday, and keep the storm below hurricane strength. Given 99L's current southward motion and the possibility that the center will relocate farther to the east later today, this makes a track to the southwest towards Honduras more likely, I predict. NHC is giving 99L a 70% chance of developing into a tropical depression by Friday, which is a reasonable forecast. I expect this will become Tropical Storm Richard by Friday.


Figure 1. Afternoon satellite image of Invest 99L.

Death toll from Super Typhoon Megi in the Philippines remarkably low
The power is still out and communications are down over the majority of the northern portion of the Philippines' Luzon Island blasted by Typhoon Megi yesterday, so the full extent of the destruction wrought by the great storm is still unclear. However, the death toll from the great storm stands at only 19, reflecting the superior effort Philippines officials made to evacuate low-lying areas and get people out of locations prone to flash flooding and mudslides. Previous major typhoons to strike the Philippines have nearly always killed hundreds, and sometime thousands, so the preparation and evacuation efforts for Megi likely saved hundreds of lives. Megi hit Luzon on Monday morning at 3:30 UTC as a Category 5 super typhoon with sustained winds of 165 mph and a central pressure of 914 mb. Severe damage was done to Isabela Province in northern Luzon, and media reports indicate that 200,000 people are homeless.


Figure 2. Visible MODIS satellite image of Megi from NASA's Aqua satellite taken at 1:30am EDT October 20, 2010. At the time, Megi was a Category 4 typhoon with 135 mph winds. Image credit: NASA.

Passage over Luzon Island destroyed Megi's eyewall and inner core region, and the storm compensated by expanding and intensifying the portions of its circulation that were over water. Now that its center is back over water in the South China Sea, Megi has re-developed its inner core and has intensified into a formidable Category 3 typhoon with 125 mph winds. Megi has been able to maintain its larger size, and is now a much larger typhoon than when it hit the Philippines. This is similar to what happened to Hurricane Ike in 2008 when it passed over Cuba, and helped give Ike a very destructive storm surge when it came ashore over Texas. Wind shear is a low 5 - 10 knots over Megi, and the waters of the South China Sea have a very high total heat content to great depth, so Megi should be able to remain a very dangerous major typhoon through Friday. The larger size of Megi means that it will be able to deliver a significant storm surge in excess of ten feet to the coast of China of Friday or Saturday, when the storm is expected to make landfall north of Hong Kong. As the storm approaches the coast on Friday, wind shear is expected to rise to the moderate or high range, and the total heat content of the ocean will drop significantly, so some weakening is to be expected. Still, Megi will probably hit China as a major Category 3 typhoon, or as a strong Category 2, bringing a significant storm surge, high winds, and widespread torrential rains that will likely make this a multi-billion dollar disaster for China. The outer rain bands of Megi are already affecting the coast of China north of Hong Kong, as seen on Hong Kong radar and Taiwan radar.


Figure 3. Still frame of damage to NE Luzon Island from a video posted to YouTube by storm chaser James Reynolds of typhoonfury.com.

Next update
I'll have an update Thursday morning.

Jeff Masters

Hurricane

Updated: 7:14 PM GMT on October 20, 2010

Permalink

Western Caribbean disturbance 99L near tropical depression strength

By: JeffMasters, 1:33 PM GMT on October 20, 2010

A tropical disturbance (Invest 99L) near the Cayman Islands is drifting eastwards towards Jamaica, and has changed little in organization this morning, but is very close to tropical depression status. The storm is bringing heavy rain to the Cayman Islands; 3.85" inches has fallen over the past 48 hours at Savannah on Grand Cayman Island. Heavy rains will continue over the Cayman Islands today and spread to western Jamaica this afternoon. Recent satellite imagery shows that 99L has a well-defined surface circulation, but the center is exposed to view and 99L has a relatively meager amount of heavy thunderstorm activity. Wind shear is marginal for development, 15 - 20 knots, due to the clockwise flow of air around an upper-level high pressure system near the coast of Honduras. The high is bringing strong upper-level winds out of the southwest to 99L. Water vapor satellite loops show considerable dry air to the west and north of 99L, and the strong southwesterly winds over the storm are bringing some of this dry into into the core of the storm, keeping all the heavy thunderstorm development confined to the east side of the center. The waters beneath 99L are very warm, 29°C, but 99L will not be able to take advantage of these warm waters until the shear relaxes. The Hurricane Hunters will be in 99L around 11am EDT this morning to see if the storm is indeed a tropical depression.

Forecast for 99L
The latest SHIPS model forecast predicts that wind shear over the Western Caribbean will stay marginal for development, 15 - 25 knots, for the remainder of today, then decline to the moderate range, 10 - 20 knots, on Tuesday, as 99L positions itself more underneath the upper-level high near the coast of Honduras. Any motion by 99L to the southwest will tend to decrease the shear over 99L, and any motion to the north or east will increase the shear, so 99L's current eastwards drift is detrimental for development. Steering currents will be weak Wednesday through Friday in the Western Caribbean, making it difficult to predict where 99L may wander to, and how much shear might affect the storm. By Saturday, a ridge of high pressure is expected to build in to the north of 99L, forcing the storm on a generally westward track. This should allow 99L to find an environment with less shear. The GFDL and HWRF model predicts a more west-northwestward track, with 99L passing through the Yucatan Channel between Cuba and Mexico on Sunday or Monday as a hurricane. The GFS, ECMWF, and NOGAPS models predict a more west-southwesterly path, with 99L making landfall in Belize Sunday or Monday. NHC is giving 99L a 70% chance of developing into a tropical depression by Friday; I'd put these odds at 80%, and expect this will become Tropical Storm Richard by Thursday.


Figure 1. Morning satellite image of Invest 99L.

Death toll from Super Typhoon Megi in the Philippines remarkably low
The power is still out and communications are down over the majority of the northern portion of the Philippines' Luzon Island blasted by Typhoon Megi yesterday, so the full extent of the destruction wrought by the great storm is still unclear. However, the death toll from the great storm stands at only 19, reflecting the superior effort Philippines officials made to evacuate low-lying areas and get people out of locations prone to flash flooding and mudslides. Previous major typhoons to strike the Philippines have nearly always killed hundreds, and sometime thousands, so the preparation and evacuation efforts for Megi likely saved hundreds of lives. Megi hit Luzon on Monday morning at 3:30 UTC as a Category 5 super typhoon with sustained winds of 165 mph and a central pressure of 914 mb. Severe damage was done to Isabela Province in northern Luzon, and media reports indicate that 200,000 people are homeless.


Figure 2. Visible MODIS satellite image of Megi from NASA's Aqua satellite taken at 1:30am EDT October 20, 2010. At the time, Megi was a Category 4 typhoon with 135 mph winds. Image credit: NASA.

Passage over Luzon Island destroyed Megi's eyewall and inner core region, and the storm compensated by expanding and intensifying the portions of its circulation that were over water. Now that its center is back over water in the South China Sea, Megi has re-developed its inner core and has intensified into a formidable Category 4 typhoon with 135 mph winds. Megi has been able to maintain its larger size, and is now a much larger typhoon than when it hit the Philippines. This is similar to what happened to Hurricane Ike in 2008 when it passed over Cuba, and helped give Ike a very destructive storm surge when it came ashore over Texas. Wind shear is a low 5 - 10 knots over Megi, and the waters of the South China Sea have a very high total heat content to great depth, so Megi should be able to remain a very dangerous major typhoon through Friday. The larger size of Megi means that it will be able to deliver a significant storm surge in excess of ten feet to the coast of China of Friday or Saturday, when the storm is expected to make landfall north of Hong Kong. As the storm approaches the coast on Friday, wind shear is expected to rise to the moderate or high range, and the total heat content of the ocean will drop significantly, so some weakening is to be expected. Still, Megi will probably hit China as a major Category 3 typhoon, bringing a significant storm surge, high winds, and widespread torrential rains that will likely make this a multi-billion dollar disaster for China. The outer rain bands of Megi are already affecting the coast of China north of Hong Kong, as seen on Hong Kong radar and Taiwan radar.


Figure 3. Still frame of damage to NE Luzon Island from a video posted to YouTube by storm chaser James Reynolds of typhoonfury.com.

Next update
I'll have an update later today, with the timing depending upon what the Hurricane Hunters find.

Jeff Masters

Hurricane

Permalink

99L a threat to develop; damage from Typhoon Megi still largely unknown

By: JeffMasters, 1:38 PM GMT on October 19, 2010

Heavy thunderstorm activity has increased and grown more organized this morning over the southwestern Caribbean between Honduras and the Cayman Islands, in association with a tropical disturbance (Invest 99L). The storm is bringing heavy rain to the Cayman Islands; two inches has fallen so far this morning at Savannah on Grand Cayman Island. Recent satellite imagery shows that 99L has some rotation, and the winds on the northeast coast of Honduras at Puerto Lempira have shifted to the west-northwest, implying that 99L may be developing a surface circulation. Wind shear is a moderate 10 - 20 knots, which is low enough to allow some slow development. Water vapor satellite loops reveal that the atmosphere in the Western Caribbean is moist enough to support development, and the waters beneath are plenty warm, at 29°C. The latest SHIPS model forecast predicts that wind shear over the Western Caribbean will mostly remain in the moderate range, 10 - 20 knots, for the remainder of the week. The current north-northwest motion of 99L should continue until Wednesday, when a strong ridge of high pressure is forecast to build in, forcing 99L to the south or west. However, steering currents will be weak Wednesday through Friday, making it difficult to predict where 99L may wander to. The only models that develop 99L are the GFDL and HWRF. The GFDL model predicts that 99L will spend enough time over water to develop into a hurricane, and brings the storm to the coast of Mexico's Yucatan Peninsula on Sunday morning. The HWRF model has 99L making landfall over Honduras late this week, before the storm has a chance to develop into a hurricane. NHC is giving 99L a 40% chance of developing into a tropical depression by Thursday. I believe the odds are higher, near 60%. The Hurricane Hunters are on call to investigate 99L this afternoon.


Figure 1. Morning satellite image of Invest 99L.

Damage from Super Typhoon Megi still largely unknown
The power is still out and communications are down over the majority of the northern portion of the Philippines' Luzon Island blasted by Typhoon Megi yesterday, so the extent of the destruction wrought by the great storm is still largely unknown. Preliminary news reports indicate that at least 10 people died, and the northern Philippine province of Isabela suffered severe damage. Megi hit Luzon on Monday morning at 3:30 UTC as a Category 5 super typhoon with sustained winds of 165 mph and a central pressure of 914 mb. Baguio near the west coast of northern Luzon received 7.72" of rain from the storm, and many mountainous regions likely received over a foot of rain.


Figure 2. Rainfall rates in excess of 1 inch per hour (orange colors) were observed by the polar-orbiting F-18 satellite in association with Megi at 00:40 UTC October 19, 2010. Image credit: Navy Research Lab, Monterey.

Passage over Luzon Island destroyed Megi's eyewall and inner core region, and the storm compensated by expanding and intensifying the portions of its circulation that were over water. Now that its center is back over water in the South China Sea, Megi has re-developed its inner core and has built a formidable new eyewall. At the same time, Megi has been able to maintain its larger size, and is now a much larger typhoon than when it hit the Philippines. This is similar to what happened to Hurricane Ike in 2008 when it passed over Cuba, and helped give Ike a very destructive storm surge when it came ashore over Texas. Wind shear is a low 5 - 10 knots over Megi, and the waters of the South China sea have a very high total heat content to great depth, so Megi should be able to intensify into a very dangerous Category 4 storm by Thursday. The larger size of Megi means that it will be able to deliver a significant storm surge in excess of ten feet to the coast of China of Friday or Saturday, when the storm is expected to make landfall near Hong Kong. As the storm approaches the coast on Friday, wind shear is expected to rise to the moderate or high range, and the total heat content of the ocean will drop significantly, so some weakening is to be expected. Still, Megi will probably hit China as a major Category 3 typhoon,bringing a significant storm surge, high winds, and widespread torrential rains that will likely make this a multi-billion dollar disaster for China.

"Daily Downpour" airing this afternoon
Our live Internet radio show, "Daily Downpour", will be airing today at 4pm EDT. The call in number is 415-983-2634, or you can post a question to broadcast@wunderground.com. You can tune in at http://www.wunderground.com/wxradio/wubroadcast.h tml, and I'll be discussing the latest info on Invest 99L with hosts Shaun Tanner and Tim Roche.

Jeff Masters

Hurricane

Updated: 6:33 PM GMT on January 03, 2012

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Category 5 Super Typhoon Megi hits the Philippines

By: JeffMasters, 1:23 PM GMT on October 18, 2010

Super Typhoon Megi hit northern Luzon Island in the Philippines near 3:30 UTC this morning as a Category 5 Super Typhoon with sustained winds of 165 mph and a central pressure of 914 mb, as rated by the Navy Research Lab in Monterey. Megi is the strongest Category 5 tropical cyclone to make landfall in the world since August 21 2007, when Hurricane Dean hit Mexico's Yucatan Peninsula with sustained winds of 175 mph and central pressure of 905 mb. We were fortunate to get precise measurements of Megi's intensity yesterday morning thanks to the Hurricane Hunters, who were investigating the typhoon in support of the Interaction of Typhoon and Ocean Project (ITOP), which is studying how the ocean responds to typhoon growth and movement in the Western Pacific Ocean. A C-130 hurricane hunter aircraft penetrated into Megi at 10,000 feet, and found an extraordinarily intense storm. At 9:05am EDT on Sunday (13:09 UTC), the aircraft recorded a central pressure in Megi of 890 mb. This is a phenomenally low pressure, ranking Megi (unofficially) as the 16th strongest tropical cyclone in world history. Only two Atlantic hurricane have been more intense than Megi--Wilma (2005) at 882 mb, and Gilbert (1988) at 888 mb. As they penetrated Megi's eyewall, the Hurricane Hunters performed the standard practice of maintaining a constant "pressure altitude"--the altitude one would expect to find a 700 mb pressure at in an atmosphere at standard conditions. In order to maintain a constant pressure altitude of 10,000 feet, the aircraft was forced to descend 3,000 feet in altitude as it entered Megi's eye. The aircraft entered the eye at 7,000 feet, so the pressure in Megi's eye was what one would normally find at an altitude 3,000 feet higher in the atmosphere. The aircraft recorded a remarkable increase in temperature of 12°C (22°F) as it crossed from the eyewall into the warm eye of Megi. A 12°C rise in eye temperature is extraordinarily rare in a tropical cyclone. Equally noteworthy were Megi's winds. The Hurricane Hunters measured winds at flight level of 220 mph, which normally translates to a surface wind speed of 198 mph, using the standard 10% reduction. The SFMR surface wind measurement instrument recorded surface winds of 186 mph in regions where heavy rain was not contaminating the measurement, but found surface winds of 199 mph in one region of heavy rain. Now, this measurement is considered contaminated by rain, but at very high wind speeds, the contamination effect is less important than at lower hurricane wind speeds, and it is possible than Megi's surface winds reached sustained speeds of 200 mph. However, data from a dropsonde in the eyewall at the time supported giving Megi just 180 mph sustained winds. This is still a ridiculously strong wind, equivalent to a violent EF-4 tornado on the Enhanced Fujita Scale.


Figure 1. Visible satellite image of Megi taken by NASA's Terra satellite at 2:25 UTC October 18, 2010. Image credit: NASA.

Passage over Luzon Island has weakened Megi to a still-formidable Category 3 typhoon with 125 mph winds, and Megi is pounding the northern portion of the island with torrential rains. We don't have many cities in the Philippines along Megi's path that report weather conditions, so it is difficult to know how strong the storm is. Tuguegarao, to the north of where Megi's eyewall passed, bottomed out at 978 mb pressure, had top sustained winds of 27 mph, and picked up 3.23" of rain thus far from the storm. Megi's rains, which will likely accumulate to more than a foot along a wide swath of northern Luzon (Figure 2), will create dangerous mudslides and life-threatening flash floods. Once Megi crosses Luzon, the storm is expected to re-intensify and hit the Chinese coast between Hainan Island and Hong Kong as a major typhoon on Friday.


Figure 2. Rainfall forecast for the 24 hours ending at 8pm EDT October 18, 2010, based on satellite estimates of Megi's rainfall rate. Rainfall amounts in excess of 12 inches (red colors) were predicted along a wide swath of Luzon Island. Image credit: NOAA/NESDIS.

Caribbean disturbance 99L
Heavy thunderstorm activity has increased over the past day over the southwestern Caribbean off the coasts of Nicaragua and Honduras in association with a tropical disturbance (Invest 99L). Recent satellite imagery does show this disturbance has some rotation, and wind shear is a moderate 10 - 20 knots, which is low enough to allow some slow development. However, the disturbance is headed west-northwest at 5 - 10 mph, and most of the computer models predict the storm will move over Nicaragua on Tuesday, which would not give 99L enough time over water to develop into a tropical depression. NHC is giving 99L a 30% chance of developing into a tropical depression by Tuesday. The storm will bring very heavy rains of 3 - 6" to northern Honduras and northeast Nicaragua over the next two days.

Next update
I'll have an update Tuesday morning.

Jeff Masters

Hurricane

Permalink

Potentially catastrophic Super Typhoon Megi approaching the Philippines

By: JeffMasters, 5:21 PM GMT on October 17, 2010

The world's strongest tropical cyclone of 2010 is Super Typhoon Megi, which intensified into an extremely dangerous Category 5 super typhoon with 180 mph winds this morning. We are fortunate to have a hurricane hunter aircraft in Megi, as part of the Interaction of Typhoon and Ocean Project (ITOP), which is studying how the ocean responds to typhoon growth and movement in the Western Pacific Ocean. As part of ITOP, a C-130 hurricane hunter aircraft was in Megi this morning, and measured some truly remarkable winds and pressures. At 8:09am EDT (12:09 UTC), the aircraft measured winds at flight level (8,000 feet) of 220 mph. The SFMR surface wind measurement instrument recorded surface winds of 186 mph in regions where heavy rain was not contaminating the measurement, but found surface winds of 199 mph in one region of heavy rain. Now, this measurement is considered contaminated by rain, but at very high wind speeds, the contamination effect is less important than at lower hurricane wind speeds, and it is possible than Megi's surface winds are close to a sustained 200 mph. This is supported by the flight level winds of 220 mph, which support surface winds of 199 mph, using the usual 10% reduction rule of thumb. The Hurricane Hunters measured a surface pressure of 893 mb at 12 UTC. This is a phenomenally low pressure, ranking Megi as the 20th strongest typhoon ever recorded in the Western Pacific. Only three Atlantic hurricane have been more intense than Megi--Wilma (2005) at 882 mb, Gilbert (1988) at 888 mb, and the 1935 Labor Day Hurricane, at 892 mb. Megi's intensity easily beats out 2010's other two Category 5 storms, March's Tropical Cyclone Ului in the South Pacific and the East Pacific's Hurricane Celia of June, which both peaked at 160 mph winds. It is still possible that Megi will intensify further, as wind shear is low, less than 10 knots, SSTs are very warm, and the ocean has a very high total heat content.


Figure 1. Visible satellite image of Megi taken by NASA's Terra satellite at 1am EDT Sunday October 17, 2010. Image credit: NASA.

Megi is poised to deal a devastating blow to the northern portion of the Philippines' Luzon Island early Monday morning. If the super typhoon's winds stay near 180 mph, the damage will be catastrophic in the regions where the eyewall makes landfall. The Philippines government is taking Megi very seriously, and has ordered evacuation of all low-lying regions in Megi's path. Equally dangerous will be Megi's torrential rains, which will likely be more than 12 inches over wide regions of northern Luzon, creating dangerous mudslides and life-threatening flash floods. Once Megi crosses Luzon, the storm is expected to re-intensify and hit the Chinese coast between Hainan Island and Hong Kong as a major typhoon on Friday. Storm chaser James Reynolds is in northeast Luzon, and will be shooting pictures and video that he will upload his website typhoonfury.com, and Twitter, @TyphoonFury.

Caribbean disturbance 99L
Heavy thunderstorm activity is currently limited over the southern Caribbean waters just north of Panama in association with a tropical disturbance (Invest 99L). Recent satellite imagery does show this disturbance has some rotation, and wind shear is a moderate 10 - 20 knots, which is low enough to allow some slow development. However, the disturbance is headed west at about 5 mph, and all of the major models predict the storm will move over Nicaragua by Tuesday, limiting any chance for development into a tropical depression.

Next update
I'll have an update Monday morning.

Jeff Masters

Hurricane

Updated: 5:24 PM GMT on October 17, 2010

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September 2010: 4th or 8th warmest on record for the globe

By: JeffMasters, 10:53 AM GMT on October 16, 2010

September 2010 was the globe's eighth warmest September on record, according to the National Oceanic and Atmospheric Administration (NOAA) National Climatic Data Center (NCDC). NASA's Goddard Institute for Space Studies rated September 2010 the fourth warmest September on record. Both NOAA and NASA rated the year-to-date period, January - September, as the warmest such period on record. September 2010 global ocean temperatures were the ninth warmest on record, and land temperatures were also the ninth warmest on record. Global satellite-measured temperatures for the lowest 8 km of the atmosphere were the warmest on record, according to both Remote Sensing Systems data and University of Alabama Huntsville data. The year-to-date period January-September is the 2nd warmest such period in the satellite data, behind 1998.

For those interested, NCDC has a page of notable weather highlights from September 2010.


Figure 1. Departure of temperature from average for September 2010. Image credit: National Climatic Data Center (NCDC).

Fourteenth warmest September on record for the U.S.
For the contiguous U.S., it was the 14th warmest September in the 116-year record, according to the National Climatic Data Center. The year-to-date period, January to September, was the 24th warmest such period on record. Ten states had a top-ten warmest September on record--Rhode Island, Maine, New Hampshire, Connecticut, Massachusetts, New Jersey, Florida, Colorado, New Mexico, and Arizona. No states recorded a top-ten coldest September.

U.S. precipitation near average
For the contiguous U.S., September 2010 ranked near average. However, there were large regional variations in precipitation. Wyoming had its driest September in the 116-year record, and three other states had top-ten driest Septembers--Louisiana, Mississippi, and Florida. Minnesota had its wettest September on record, and five other states had a top-ten wettest September--North Dakota, South Dakota, Washington, Wisconsin, and Missouri.

La Niña intensifies to the "strong" category
The equatorial Eastern Pacific Ocean is now experiencing strong La Niña conditions. Sea surface temperatures (SSTs) over the tropical Eastern Pacific in the area 5°N - 5°S, 120°W - 170°W, also called the "Niña 3.4 region", dropped to 1.8°C below average during the first two weeks of October, according to NOAA. The Australian Bureau of Meteorology put this number at 1.53°C below average (as of October 10.) Moderate La Niña conditions are defined as occurring when this number is 1.0°C - 1.5°C below average. Temperatures colder than 1.5°C below average qualify as strong La Niña conditions. NOAA is maintaining its La Niña advisory, and expects La Niña conditions to last through the coming winter into spring.

Both El Niño and La Niña events have major impacts on regional and global weather patterns. For the remainder of October, we can expect La Niña to bring cloudier and wetter than average conditions to the Caribbean, but weather patterns over North America should not see much impact. La Niña typically causes warm, dry winters over the southern portion of the U.S., with cooler and wetter than average conditions over the Pacific Northwest. The Ohio and Mississippi Valleys states typically have wetter winters than usual.

September 2010 Arctic sea ice extent 3rd lowest on record
Northern Hemisphere sea ice extent in September 2010 was the third lowest in the 31-year satellite record behind 2007 and 2008, according to the National Snow and Ice Data Center. Ice volume in September was the lowest on record, according to University of Washington Polar Ice Center. The reported volume of 1,000 cubic miles (4,000 cubic kilometers) was 70 percent below the 1979 - 2009 September average of 3,200 cubic miles (13,400 cubic kilometers). Sea ice volume accounts for sea ice extent as well as the thickness of ice beneath the ocean's surface. The Northwest Passage through the normally ice-choked waters of Canada, as well as the Northeast Passage along the coast of northern Russia, remained open for ice-free navigation for most of September, but are now frozen shut again. This is the third consecutive year--and third time in recorded history--that both passages have melted open. Mariners have been attempting to sail these passages since 1497, and 2005 was the first year either of these passages reported ice-free conditions; 2008 was the first year both passages melted free. The 2010 Arctic melt season allowed for two sailing expeditions--one Russian and one Norwegian--to successfully navigate both the Northeast Passage and the Northwest Passage in a single season, the first time this feat has occurred in modern history.

New Caribbean disturbance
Heavy thunderstorm activity is currently limited over the southern Caribbean waters just north of Panama, but the latest 2am EDT (6Z) NOGAPS and GFS model runs continue to predict the formation of a tropical depression in the region 3 - 5 days from now. The NOGAPS model predicts that the storm will move northwest towards the Cayman Islands, while the GFS model takes the storm west-northwest over Nicaragua and Honduras. NHC is giving the disturbance a 10% chance of developing into a tropical depression by Monday. Northeastern Nicaragua and Honduras can expect a period of very heavy rains from the disturbance Saturday night through Tuesday.


Figure 2. Visible satellite image of Megi at 3:30am EDT 10/16/10. Image credit: Navy Research Lab, Monterey.

Typhoon Megi
In the Western Pacific, Typhoon Megi has attained Category 3 strength, and is predicted to intensify into a 150 mph supertyphoon that will strike the northern Philippine Island of Luzon on Monday morning. If this forecast verifies, Megi would be the strongest tropical cyclone to strike land globally in 2010. The globe has had an unusually low number of landfalling major hurricanes this year. Only one Category 4 or stronger storm has hit land--Tropical Cyclone Tomas, which hit Fiji on March 15 as a Category 4 storm with 135 mph winds. Tomas killed 3 people and did $45 million in damage to Fiji, and was the strongest storm to hit Fiji since Cyclone Bebe in 1972. The only other major tropical cyclones in 2010 to make landfall were Tropical Cyclone Oli, which passed through French Polynesia on February 5 as a Category 3 storm; Tropical Cyclone Rene, which hit Tonga in the South Pacific as a Category 3 storm on February 15; Typhoon Fanapi, which hit Taiwan on September 19 as a Category 3 storm; and Hurricane Karl, which hit Mexico near Veracruz on September 17 as a Category 3 hurricane.

Next update
I'll have an update Sunday or Monday morning.

Jeff Masters

Climate Summaries

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Paula dying; Zambia records its hottest temperature in history

By: JeffMasters, 12:35 PM GMT on October 15, 2010

There's not much left of Tropical Depression Paula, which continues to weaken as wind shear of 35 - 40 knots tears the storm apart. Satellite imagery shows Paula has the classic appearance of a storm experiencing high wind shear--a low-level center exposed to view, with all the heavy thunderstorm activity pushed to the northeast side by powerful upper-level winds from the southwest. Paula caused only minor flooding and very little damage in Mexico, Cuba, and the Florida Keys. Considering that most Category 2 hurricanes that pass through the Yucatan Channel end up getting their names retired, we got very fortunate with Paula. Havana, Cuba reported sustained winds of 41 mph, gusting to 54, at 7pm local time last night, and received heavy rain that caused moderate street flooding. The wind and rain knocked out power to most of the city and felled over 400 trees. Some isolated heavy rains affected the Florida Keys, with Key West picking up 1.40" inches of rain. Paula will bring some heavy rain showers to Andros Island in the Bahamas today, but the storm is not likely to cause any more flooding problems. High wind shear should be able to completely destroy Paula by Saturday morning.


Figure 1. Visible MODIS image from NASA's Terra satellite of Paula at 12:05pm EDT October 14, 2010, as Paula was approaching Havana, Cuba. Image credit: NASA.

New Caribbean disturbance
Heavy thunderstorm activity is currently limited over the southern Caribbean waters just north of Panama, but the latest 2am EDT (6Z) NOGAPS and GFS model runs continue to predict the formation of a tropical depression in the region 4 - 5 days from now. The storm is predicted to move northwest or northwards towards the Cayman Islands and Jamaica once it forms. The GFS model has been pretty reliable in forecasting the genesis of new tropical depressions this year, and the fact that we have two major models predicting the formation of a new Caribbean tropical depression next week is worth paying attention to.

Typhoon Megi
In the Western Pacific, Typhoon Megi has attained Category 2 strength, and is predicted to intensify into a 150 mph supertyphoon that will strike the northern Philippine Island of Luzon on Sunday night or Monday morning. If this forecast verifies, Megi would be the strongest tropical cyclone to strike land globally in 2010. The globe has had an unusually low number of landfalling major hurricanes this year. Only one Category 4 or stronger storm has hit land--Tropical Cyclone Tomas, which hit Fiji on March 15 as a Category 4 storm with 135 mph winds. Tomas killed 3 people and did $45 million in damage to Fiji, and was the strongest storm to hit Fiji since Cyclone Bebe in 1972. The only other major tropical cyclones in 2010 to make landfall were Tropical Cyclone Oli, which passed through French Polynesia on February 5 as a Category 3 storm; Tropical Cyclone Rene, which hit Tonga in the South Pacific as a Category 3 storm on February 15; Typhoon Fanapi, which hit Taiwan on September 19 as a Category 3 storm; and Hurricane Karl, which hit Mexico near Verzcruz on September 17 as a Category 3 hurricane.

Zambia hits an all-time record 42.4°C (108.3°F)
Zambia recorded its hottest temperature in history Wednesday, October 13, when the mercury hit 42.4°C (108.3°F) in Mfuwe. The previous record was 42.3°C (108.1°F) set on November 17, 2005 in Mfuwe. Zambia is near the Equator, and the timing of the rainy season and dry season determines when all-time maximum and minimum temperatures can be set. It turns out that the months of September, October, and November mark a transition period into Zambia's rainy season, and are the only months of the year that all-time record high temperatures are likely to occur (thanks go to Maximiliano Herrera for pointing this out.) Zambia is the 18th nation to record a hottest all-time temperature this year, which is a new record. The year 2007 is in second place, with 15 such records. No nations have recorded an all-time coldest temperature so far this year; I regret erroneously reporting earlier in my blog that Guinea had done so. Guinea actually had its coldest temperature in history last year, on January 9, 2009, when the mercury hit 1.4°C (34.5°F) at Mali-ville in the Labe region. The full updated list of national heat records set in 2010 is below; my source for extreme weather records is the excellent book Extreme Weather by Christopher C. Burt, who is now a featured blogger on wunderground. I thank Chris and weather record researchers Maximiliano Herrera and Howard Rainford for their assistance identifying this year's new extreme temperature records.


Figure 2. Climate Central put together a nice graphic showing the nations that have set new extreme heat records in 2010, which I've updated to include Zambia.

National heat records set in 2010
Bolivia tied its all-time hottest temperature mark on October 29, when the mercury hit 46.7°C (116.1°F) at Villamontes. This ties the record set in Villamontes on three other dates: November 9, 2007, November 1980, and December 1980.

Zambia recorded its hottest temperature in history Wednesday, October 13, when the mercury hit 42.4°C (108.3°F) in Mfuwe. The previous record was 42.3°C (108.1°F) set on November 17, 2005 in Mfuwe.

Belarus recorded its hottest temperature in its history on August 6, 2010, when the mercury hit 38.9°C (102.0°F) in Gorky. The previous record was 38.0°C (100.4°F) set at Vasiliyevichy on Aug. 20, 1946.

Ukraine recorded its hottest temperature in its history when the mercury hit 42.0°C (107.6°F) at Lukhansk on August 12, 2010. The previous record was set at the same location on August 1, 2010--41.3°C (106.3°F). Ukraine also reached 41.3°C on July 20 and 21, 2007, at Voznesensk.

Cyprus recorded its hottest temperature in its history on August 1, 2010 when the mercury hit 46.6°C (115.9°F) at Lefconica. The old record for Cyprus was 44.4°C (111.9°F) at Lefkosia in August 1956. An older record of 46.6°C from July 1888 was reported from Nicosia, but is of questionable reliability.

Finland recorded its hottest temperature on July 29, 2010, when the mercury hit 37.2°C (99°F) at Joensuu. The old (undisputed) record was 95°F (35°C) at Jyvaskyla on July 9, 1914. The previous official record was 35.9°C at Turku in July 1914, but this reading has been disputed by weather records researcher Maximiliano Herrera as being unreliable due improper siting of the instrument too close to tall buildings.

Qatar had its hottest temperature in history on July 14, 2010, when the mercury hit 50.4°C (122.7°F) at Doha Airport. The previous record was 49.6°C in July 2000 at the same location. There are other stations in Qatar,but only the Doha International Airport has reliable data.

Russia had its hottest temperature in history on July 12, when the mercury rose to 45.4°C (113.7°F) at the Utta hydrological station in the Kalmykia Republic, in the European portion of Russia near the Kazakhstan border. This station is not under control of the Russian meteorological service, and may not be 100% reliable. A reading of 44.0°C (111.2°F) was also recorded in Yashkul, Kalmykia Republic, on July 11. The previous hottest temperature in Russia (not including the former Soviet republics) at a non-automated station was the 43.8°C (110.8°F) reading measured at Alexander Gaj, Kalmykia Republic, on August 6, 1940. The previous hottest temperature at an automated station was 45.0°C recorded in August 1940 at El'ton. The remarkable heat in Russia this year has not been limited just to the European portion of the country--the Asian portion of Russia also recorded its hottest temperature in history this year, a 42.7°C (108.9°F) reading at Ust Kara, in the Chita Republic on June 27. The 42.3°C (108.1°F) reading on June 25 at Belogorsk, near the Amur River border with China, also beat the old record for the Asian portion of Russia. The previous record for the Asian portion of Russia was 41.7°C (107.1°F) at Aksha on July 21, 2004.

Sudan recorded its hottest temperature in its history on June 22 when the mercury rose to 49.7°C (121.5°F) at Dongola. The previous record was 49.5°C (121.1°F) set in July 1987 in Aba Hamed.

Niger tied its record for hottest day in history on June 22, 2010, when the temperature reached 47.1°C (116.8°F) at Bilma. That record stood for just one day, as Bilma broke the record again on June 23, when the mercury topped out at 48.2°C (118.8°F). The previous record was 47.1°C on May 24, 1998, also at Bilma.

Saudi Arabia had its hottest temperature ever on June 22, 2010, with a reading of 52.0°C (125.6°F) in Jeddah, the second largest city in Saudi Arabia. The previous record was 51.7°C (125.1°F), at Abqaiq, date unknown. The record heat was accompanied by a sandstorm, which caused eight power plants to go offline, resulting in blackouts to several Saudi cities.

Chad had its hottest day in history on June 22, 2010, when the temperature reached 47.6°C (117.7°F) at Faya. The previous record was 47.4°C (117.3°F) at Faya on June 3 and June 9, 1961, but old readings at this station, particularly in the 1950s, were affected by over-exposure of the instrument to sun.

Kuwait recorded its hottest temperature in history on June 15 in Abdaly, according to the Kuwait Met office. The mercury hit 52.6°C (126.7°F). Kuwait's previous all-time hottest temperature was 51.9°C (125.4°F), on July 27,2007, at Abdaly. Temperatures reached 51°C (123.8°F) in the capital of Kuwait City on June 15, 2010. There were some readings as high as 54°C at Mitribah this summer, but the intrument there was found to be out of calibration.

Iraq had its hottest day in history on June 14, 2010, when the mercury hit 52.0°C (125.6°F) in Basra. Iraq's previous record was 51.7°C (125.1°F) set August 8, 1937, in Ash Shu'aybah.

Pakistan had its hottest temperature in history on May 26, when the mercury hit an astonishing 53.5°C (128.3°F) at the town of MohenjuDaro, according to the Pakistani Meteorological Department. While this temperature reading must be reviewed by the World Meteorological Organization (WMO) for authenticity, not only is the 128.3°F reading the hottest temperature ever recorded in Pakistan, it is the hottest reliably measured temperature ever recorded on the continent of Asia. The old Pakistani record was 52.8°C (127°F) at Jacobabad in 1919.

Myanmar (Burma) had its hottest temperature in its recorded history on May 14, when the mercury hit 47.2°C (117.0°F) in Myinmu. This broke the record of 47.0°C set at the same location two days previous (May 12.) Myanmar's previous hottest temperature was 46.0°C (114.4°F) at Magwe in May, 1980. According to Chris Burt, author of the authoritative weather records book Extreme Weather, the 47.2°C measured this year is the hottest temperature in Southeast Asia history.

Ascension Island (St. Helena, a U.K. Territory) had its hottest temperature in history on March 25, 2010, when the mercury hit 34.9°C (94.8°F) at Georgetown. The previous record was 34.0°C (93.2°F) at Georgetown in April 2003, exact day unknown.

The Solomon Islands had their hottest temperature in history on February 1, 2010, when the mercury hit 36.1°C (97°F) at Honiara Henderson. The previous record for the Solomon Islands was 35.6°C (96.0°F) at Honaiara, date unknown.

Colombia had its hottest reliably measured temperature in history on January 24, 2010, when Puerto Salgar hit 42.3°C (108°F). The previous record was 42.0°C (107.6°F) at El Salto in March 1988 and April 1998 (exact day unknown.)

Also Notable
China set its all-time heat record for an inhabited place on June 20, 2010, when the mercury hit 48.7°C (119.7°F) at Toyoq. The all-time heat record for China is 49.7°C (121.5°F) on August 3, 2008 at the Aydingkol automatic weather station at the uninhabited Ading Lake in the Turfan Depression in Northwest China.

Martinique, an island in the Caribbean that is a French territory, set what may be its hottest reliably measured temperature record in September, when the mercury hit 36.2°C (97.2°F) at Francois Chopotte. The current all-time record is 36.5°C (97.7°F) in April 1983 at St. Pierre Observatory, but this measurement was taken with older equipment that may not be reliable.

The occupied west bank of Palestine, the portion of Israel that declared independence in 1988 but is not recognized by all nations as a sovereign country, recorded its hottest temperature in history on August 7, 2010, when the temperature hit 51.4°C (124.5°F) at Kibbutz Almog (also called Qalya or Kalya) in the Jordan Valley. The previous record for this portion of Israel was set on June 22, 1942, at the same location.

All-time national heat records were missed by 1°C or less in many other nations this summer, including the Azores, Morocco, Estonia, and Latvia.

Extensive credit for researching these records goes to weather records researcher Maximiliano Herrera, who maintains a comprehensive set of extreme temperature records on his web site.

Next update
I'll have an update Saturday morning.

Jeff Masters

Heat Hurricane

Updated: 1:28 PM GMT on November 23, 2010

Permalink

Paula continuing to weaken

By: JeffMasters, 7:53 PM GMT on October 14, 2010

Data from an Air Force Hurricane Hunter aircraft indicates that Tropical Storm Paula continues to weaken. The aircraft's latest center penetration at 3:08pm EDT found top winds at their flight level of 10,000 feet of just 55 mph in the eyewall. The SFMR instrument saw surface winds near 65 mph. The eyewall of Paula has collapsed, and satellite imagery shows the storm has a lopsided appearance due to wind shear. The low-level center is almost exposed to view, the classic satellite signature of a storm under high wind shear. Since the high wind shear affecting Paula is pushing most of the storm's heavy thunderstorms to the north, Cuba is receiving very little rain from the storm. Havana has reported two brief rain squalls from Paula, and top sustained winds of just 20 mph. Sporadic heavy rains are affecting the Florida Keys today, with Key West picking up 1.01" inches of rain thus far. Weather radar out of Key West (Figure 2) noted several regions offshore where Paula has dumped 5+ inches of rain.


Figure 1. Radar image from the Pinar del Rio radar in Cuba at 3:15pm EDT on October 14, 2010, showing that Paula is now very disorganized. Image credit: Cuban Institute of Meteorology.


Figure 2. Radar-estimated precipitation for Paula from the Key West radar.

Forecast for Paula
The models continue to predict that Paula will move along the north coast of Cuba or just inland during the next two days. On this track, Paula will move over Cuba's capital, Havana, tonight and Friday morning. An extended period of time over mountainous Cuba will likely destroy a small storm like Paula by Friday night, particularly since the storm will be under 30+ knots of wind shear. The models are pretty unanimous in showing that wind shear will pull Paula apart over the next day regardless of whether or not the center stays over water. Tropical storm force winds extend out just 45 miles to the north of Paula's center, so it is unlikely that the Florida Keys will experience sustained winds of 39+ mph. The 11am EDT wind probability product from NHC gives Key West a 21% chance of receiving tropical storm force winds; these odds are 70% for Havana. Havana may receive some minor wind damage from Paula, and there may be some minor flooding problems in the mountainous regions of Cuba.

Elsewhere in the tropics
The latest 8am EDT (12Z) NOGAPS and GFS model runs continue to predict the formation of a tropical depression 4 - 5 days from now, in the southern Caribbean off the coast of Nicaragua. The storm is predicted to move northwest or northwards towards the Cayman Islands and Jamaica, once it forms. The GFS model has been pretty reliable in forecasting the genesis of new tropical depressions this year, and the fact that we have two major models predicting the formation of a new Caribbean tropical depression next week is worth paying attention to.

In the Western Pacific, Tropical Storm Megi is nearing typhoon strength, and is predicted to intensify into a major typhoon that will strike the northern Philippine Island of Luzon on Sunday night or Monday morning.

Next update
I'll have an update Friday morning.

Jeff Masters

Hurricane

Permalink

Paula's eyewall disintigrates as the storm weakens

By: JeffMasters, 1:14 PM GMT on October 14, 2010

Data from an Air Force Hurricane Hunter aircraft indicates that Hurricane Paula continues to weaken, and the storm may no longer be a hurricane. The latest 8:06am EDT center report found the pressure had risen to 1002 mb, and the aircraft saw top winds at their flight level of 10,000 feet of just 60 mph between 6am and 9am EDT. The Hurricane Hunters did not report the existence of an eyewall, and Cuban radar (Figure 1) indicates that the southern portion of the eyewall has collapsed, leaving Paula with just 1/3 of an eyewall. Paula is moving at 5 mph along the northern coast of Cuba, and is bringing heavy rains to the western portion of the island. Cabo San Antonio on the western tip of Cuba has picked up 4.85" of rain so far from Paula, and a wind gust of 60 mph was reported on the western tip of the island. Heavy rains have also hit the Florida Keys this morning, with Key West picking up 0.62" inches of rain in just 30 minutes from a heavy rain squall that ended at 7:30am EDT. Weather radar out of Key West (Figure 2) noted several regions offshore where Paula has dumped 5+ inches of rain. High wind shear due to strong upper-level winds of 30 knots out of the south are tearing Paula apart, and satellite imagery shows the storm has a lopsided appearance due to the shear, and the low-level center is almost exposed to view. Low level spiral banding is no longer as impressive, and the intensity of Paula's thunderstorms has waned significantly over the past few hours.


Figure 1. Radar image from the Pinar del Rio radar in Cuba at 8:30am EDT on October 14, 2010, showing the eye of Paula along the northwest coast of Cuba. Image credit: Cuban Institute of Meteorology.


Figure 2. Radar-estimated precipitation for Paula from the Key West radar.

Forecast for Paula
The models have come into better agreement on the future track of Paula, with the storm expected to move along the north coast of Cuba or just inland during the next three days. On this track, Paula will move over Cuba's capital, Havana, tonight and Friday morning, and bring heavy rains of 3 - 6 inches to the most populous region of the country. An extended period of time over mountainous Cuba will likely destroy a small storm like Paula within 48 hours, particularly since the storm will be under 30+ knots of wind shear. A path just off the coast will let Paula live a little longer, but not much longer. The models are pretty unanimous in showing that wind shear will pull Paula apart over the next two days regardless of whether or not the center stays over water. Tropical storm force winds extend out just 50 miles from Paula's center, so it is unlikely that the Florida Keys will experience sustained winds of 39+ mph. The 5am EDT wind probability product from NHC gives Key West a 40% chance of receiving tropical storm force winds; these odds are 83% for Havana. Havana may receive some minor wind damage from Paula, but it currently appears that heavy rain will be the major threat from Paula. The hurricane could easily dump more than ten inches over mountainous regions of Cuba, creating flooding hazards.


Figure 3. True color satellite image of Paula taken by the MODIS instrument on NASA's Aqua satellite at 2:35pm EDT October 13, 2010. Image credit: NASA.

Elsewhere in the tropics
The NOGAPS and GFS models are predicting the formation of a tropical depression 5 - 6 days from now, in the southern Caribbean off the coast of Nicaragua. The storm is predicted to move west-northwest over Nicaragua and Honduras (the NOGAPS model forecast) or northwards towards the Cayman Islands and Jamaica (the GFS model forecast.) The GFS model has been pretty reliable in forecasting the genesis of new tropical depressions this year, and the fact that we have two major models predicting the formation of a new Caribbean tropical depression next week is worth paying attention to.

In the Western Pacific, Tropical Storm Megi is nearing typhoon strength, and is predicted to intensify into a major typhoon that will strike the northern Philippine Island of Luzon on Sunday night or Monday morning.

Next update
I'll have an update this afternoon.

Jeff Masters

Hurricane

Updated: 2:10 PM GMT on October 14, 2010

Permalink

Paula weakens, heads towards Cuba

By: JeffMasters, 7:42 PM GMT on October 13, 2010

Data from an Air Force Hurricane Hunter aircraft indicates that Hurricane Paula has weakened substantially, and may now be a Category 1 hurricane. The aircraft has made three penetrations of the eye as of 3:30pm EDT, and found top surface winds of 80 mph with their SFMR instrument. Top winds seen at flight level of 10,000 feet were 92 mph, which translates to 83 mph surface winds, using the 10% reduction rule of thumb. Based on these data, it is reasonable to assume Paula is now a Category 1 hurricane with 85 - 90 mph winds, since the aircraft may not have sampled where the peak winds were occurring. Paula is in the Yucatan Channel, the narrow gap between Mexico's Yucatan Peninsula and the western tip of Cuba, and has now turned and is headed northeast towards Cuba. A rain band with heavy rains lies over the western tip of Cuba, and Cabo San Antonio on the western tip of Cuba picked up 2.80" of rain so far today from Paula. However, the winds have remained below 15 mph.


Figure 1. Radar image from the Pinar del Rio radar in Cuba at 3:15pm EDT on October 13, 2010, showing the eye of Paula near the western tip of Cuba. A strong spiral band was affecting western Cuba at this time. Image credit: Cuban Institute of Meteorology.

High wind shear due to strong upper-level winds out of the south are starting to tear up the southern portion of Paula, and satellite imagery shows the storm now has a lopsided appearance due to the shear. Low level spiral banding is no longer as impressive, and lines of low-level arc-shaped clouds are racing away from the southern portion of Paula, indicating that the hurricane has ingested dry air that has created strong thunderstorm downdrafts. Ingestion of this dry air is partially responsible for Paula's recent weakening. Water vapor satellite loops confirm the presence of a large amount of dry air on the south, west, and north sides of Paula.

Forecast for Paula
A small storm like Paula may weaken very quickly under the current 30 knots of wind shear and the dry air surrounding it. However, the latest 3pm EDT eye report from the Hurricane Hunters indicated that Paula's eyewall still remained solid, so Paula may be able to hang on for a few more hours before the shear drives dry air into the inner core and destroys the eyewall. Once that occurs, Paula should weaken more rapidly. I'd be surprised if Paula was still a hurricane on Thursday morning, even if it does not hit Cuba. Hurricane force winds extend out just fifteen miles from Paula's center, so only a very small region of coast will receive Paula's strongest winds if landfall occurs. The 11am EDT wind probability product from NHC gives Cabo San Antonio on the western tip of Cuba the highest odds of receiving hurricane force winds of any land area--a 35% chance. Key West is given a 4% chance, and Havana, Cuba, an 8% chance. These probabilities are slightly higher than they were in the 5am advisory, reflecting Paula's ability to hang tough in the face of 30 knots of wind shear. It currently appears that heavy rain will be the major threat from Paula. If Paula stalls over or near western Cuba for several days, the hurricane could easily dump more than ten inches over mountainous regions of the island.

The latest SHIPS model forecast calls for wind shear to rise to a very high 35 - 40 knots on Thursday afternoon, and remain above 25 knots for the rest of the week. This high shear, combined with the expected landfall of the center over mountainous Cuba, should be enough to destroy Paula by Sunday.

The latest set of model runs from 8am EDT (12Z) are very similar to the previous sets of runs. There are two basic solutions. One solution, championed by the GFDL and GFS ensemble mean, takes Paula just south of the Florida Keys on Friday morning, then into the Bahamas Friday afternoon. The other solution, offered by the rest of the models, is for Paula to move very slowly over western Cuba the next few days, then circle southeastwards into the Caribbean, as a strong high pressure system over the Gulf of Mexico intensifies and pushes Paula to the south. This is the more likely scenario, given the current trends in how the models are depicting evolution of the jet stream pattern over the U.S. in the coming days. However, residents of South Florida, the Keys, and the Bahamas should be anticipate the possibility of Paula coming their way as a weak tropical storm on Friday.

Elsewhere in the tropics
The NOGAPS model is predicting the formation of Tropical Storm Richard 5 - 6 days from now, in the southern Caribbean off the coast of Nicaragua, near where Paula formed. The GFS has just a strong tropical disturbance forming there.

In the Western Pacific, Tropical Storm Megi has formed, and is predicted to be a major typhoon that will threaten the northern Philippine Island of Luzon early next week.

Next update
I'll have an update Thursday morning.

Jeff Masters

Hurricane

Updated: 7:43 PM GMT on October 13, 2010

Permalink

Paula misses Mexico, stalls in Yucatan Channel

By: JeffMasters, 1:29 PM GMT on October 13, 2010

Hurricane Paula is now stationary over the Yucatan Channel, the narrow gap between Mexico's Yucatan Peninsula and the western tip of Cuba. Despite Paula's Category 2 strength and passage just 60 miles east of the Mexican coast, the hurricane has not brought tropical storm-force winds to Mexico. In Cancun, top winds measured so far this morning have been just 17 mph, with gusts to 27 mph. A modest 0.17" of rain fell between midnight and 8:21am local time. Cancun radar (Figure 1) shows that the rain bands in the tightly would core of Paula lie just offshore of Cancun this morning. Paula had little impact on Mexico's Cozumel Island as the storm passed by last night; winds remained below 20 mph during passage.


Figure 1. Radar image at 9am EDT 10/13/10 from Cancun, Mexico. The core of Paula was located 60 miles to the east of Cancun, and Paula's rainbands were remaining just offshore. Image credit: CONAGUA Mexico.

Satellite imagery shows little change to Paula has occurred this morning. The amount and intensity of the storm's heavy thunderstorms have remained about the same as last night, and satellite intensity estimates continue to support calling Paula a hurricane with 90 - 100 mph winds. The Hurricane Hunters left Paula at 4am, and will not be back until 2pm, so we will have to wait until then to get a better estimate of Paula's intensity. At that time, I expect they will find a weaker storm, as wind shear has increased to a high 25 knots, due to strong upper-level winds out of the south. Cancun Radar shows the storm has stalled and been stationary between 6am - 9am EDT; if Paula remains nearly stationary for several more hours, the hurricane may churn up cold water from the depths, causing weakening. However, Paula is currently over a patch of the deepest, warmest water in the entire North Atlantic. Waters of 26°C (79°F) or warmer extend to a depth of 400 feet (120 meters) in the Yucatan Channel, and it will take much longer than usual for a stationary hurricane in this region to significantly cool the surface waters.


Figure 2. Visible satellite image of Paula taken at 12:20pm EDT 10/12/10 by NASA's Terra satellite. Image credit: NASA.

Forecast for Paula
Paula should start moving to the northeast or east later this morning, bringing it near the tip of western Cuba late tonight or early Thursday morning. Hurricane force winds extend out just fifteen miles from Paula's center, so only a very small region of coast will receive Paula's strongest winds if landfall occurs. The 5am EDT wind probability product from NHC gives Cabo San Antonio on the western tip of Cuba the highest odds of receiving hurricane force winds of any land area--a 34% chance. Key West is given a 2% chance, and Havana, Cuba, a 6% chance. It currently appears that heavy rain will be the major threat from Paula. If Paula stalls over or near western Cuba for several days, the hurricane could easily dump more than ten inches over mountainous regions of the island.

The latest SHIPS model forecast calls for wind shear to rise to a very high 30 knots tonight, and remain about 30 knots for the rest of the week. This high shear, caused by strong upper-level winds from the south, should begin to eat away at the south side of Paula's eyewall today, causing the inner core of the storm to collapse and Paula to weaken to a tropical storm by Thursday. If Paula hits the western tip of Cuba, weakening will be hastened. Given Paula's small size, once the inner core is disrupted, the storm could weaken very quickly.

The latest set of model runs from 2am EDT (6Z) continue to show a fair degree of uncertainty about the future path of Paula. There are two basic solutions. One solution, championed by the GFDL and GFS ensemble mean, takes Paula through or just south of the Florida Keys on Friday morning, then into the Bahamas Friday afternoon. The other solution, offered by the rest of the models, is for Paula to move very slowly over western Cuba the next few days, then circle southeastwards into the Caribbean, as a strong high pressure system over the Gulf of Mexico intensifies and pushes Paula to the south. This is the more likely scenario, given the current trends in how the models are depicting evolution of the jet stream pattern over the U.S. in the coming days. However, residents of South Florida, the Keys, and the Bahamas should be anticipate the possibility of Paula coming their way as a strong tropical storm on Friday.

Elsewhere in the tropics
The NOGAPS model is predicting the formation of Tropical Storm Richard 5 - 6 days from now, in the southern Caribbean off the coast of Nicaragua, near where Paula formed. The GFS has just a strong tropical disturbance forming there.

In the Western Pacific, Tropical Storm Fifteen has formed, and is predicted to be a major typhoon that will threaten the northern Philippines early next week.

Next update
I'll have an update between 3pm - 4pm this afternoon.

Jeff Masters

Hurricane

Updated: 5:29 PM GMT on October 13, 2010

Permalink

Paula intensifies to Category 2

By: JeffMasters, 7:34 PM GMT on October 12, 2010

Hurricane Paula put on a respectable burst of intensification early this afternoon, popping an eye and reaching Category 2 strength. Last night and early this morning, Paula set a modern record for the fastest intensification from the issuance of the first advisory to hurricane strength, performing the feat in just 12 hours. At 1pm this afternoon, an Air Force hurricane hunter aircraft measured surface winds of 104 mph with their SFMR instrument in Paula's northeast eyewall. On the second pass through the eyewall at 2pm, the SFMR saw top winds of 85 mph, in Paula's northwest eyewall, and the pressure had dropped 1 mb in one hour. The aircraft passed through the northeast eyewall again near 3pm EDT, and found weaker surface winds, just 83 mph, compared to the 104 mph seen at 1pm. The pressure remained the same as at 2pm, suggesting that Paula is done intensifying. Paula is a small hurricane, with hurricane force winds that extend out just 10 miles from the center. The eye is very tight, with a diameter of 11 miles. The Hurricane Hunters noted something in their comments I've never seen before--the eye was more square than circular.


Figure 1. Radar image at 3pm EDT 10/12/10 from Cancun, Mexico, showing rain from an outer spiral band over Cozumel Island, and the core of Paula to the south-southeast of the island. Image credit: CONAGUA Mexico.

Satellite imagery has been showing the intermittent appearance of an eye this afternoon, and Paula has been growing more organized, with improving low-level spiral banding and upper-level outflow. Water vapor satellite loops indicate that the atmosphere in the Western Caribbean is moist enough to support further development, but moderate wind shear of 15 - 20 knots, due to strong upper-level winds out of the south, is slowing Paula's intensification.


Figure 2. Rain rate (inches per hour) as measured by the TRMM satellite at 12:29 pm EDT 10/12/10. Peak rain rates of 0.8 inches/hr (yellow colors) were occurring in a spiral band on Paula's west side. Lower rain rates of 0.6 inches/hr (green colors) were seen in the eyewall. Image credit: Navy Research Lab, Monterey.

Forecast for Paula
Radar from Cancun shows that an outer spiral band moved over Cozumel between 2 - 3pm EDT, bringing a brief heavy rain squall to the island. This band will move inland over the Yucatan Peninsula, bringing a brief heavy rain squall to Cancun late this afternoon. Radar and satellite imagery indicate about a six-hour break after passage of this spiral band before the next major band hits, late tonight. Tropical storm force winds of 39+ mph extend out from Paula's center about 70 miles to the north. Paula's current north-northwest motion of 10 mph means that tropical storm force winds should reach the coast of Mexico near Cozumel between 8pm - 2am local time tonight. A good way to visualize this is to use our wundermap with the "hurricane" layer turned on, and click on the "forecast" and "wind radius" boxes. Hurricane force winds extend out just ten miles from the center, so only a very small region of coast will receive Paula's strongest winds. The 1:45pm EDT wind probability product from NHC gives a 99% chance that Cozumel will receive tropical storm force winds, and a 60% chance of getting hurricane force winds of 74+ mph. In addition to high winds, heavy rain will be a major threat. If Paula stalls as expected and wanders in the region for many days, rainfall forecasts from the HWRF and GFDL models suggest that Paula will be capable of dumping more than a foot of rain in isolated regions over the next five days. The latest SHIPS model forecast calls for wind shear to rise to the high range, 25 - 40 knots, tonight through the end of the week. This high shear, combined with the dry atmosphere to the north of Paula, should limit Paula's chances of becoming a major hurricane, since the hurricane is small and vulnerable to high wind shear. NHC is giving Paula a 27% chance of becoming a major hurricane. Shear, dry air, and interaction with the land area of western Cuba and/or the Yucatan Peninsula are likely to weaken the storm below hurricane strength later this week, as suggested by most of the intensity forecast models.

The latest set of model runs from 8am EDT (12Z) still show a variety of solutions for the future path of Paula. Steering currents in the Western Caribbean will collapse on Wednesday, potentially allowing Paula to wander in the region for many days. It is also possible that Paula could get caught up in a strong trough of low pressure predicted to traverse the U.S. this week (and spawn a Nor'easter for New England this weekend.) In this scenario, offered by the GFDL model, Paula would make a sharp turn to the east-northeast, hit western Cuba, bring tropical storm-force finds to the Florida Keys on Thursday night, then move into the Bahama Islands on Friday. NHC is making the reasonable forecast of sticking with what the majority of models are saying by predicting that Paula will stall out near the western tip of Cuba. However, residents of South Florida, Central Cuba, and the Bahamas should be prepared for Paula to come their way as a strong tropical storm on Thursday and Friday.

"Hurricane Haven" airing this afternoon
My live Internet radio show, "Hurricane Haven", will be airing again today at 4pm EDT. The call in number is 415-983-2634, or you can post a question to broadcast@wunderground.com. Be sure to include "Hurricane Haven question" in the subject line.

Today's show will be about 30 minutes, and you can tune in at http://www.wunderground.com/wxradio/wubroadcast.h tml. The show will be recorded and stored as a podcast.

Jeff Masters

Hurricane

Updated: 6:35 PM GMT on January 03, 2012

Permalink

Hurricane Paula sets a rapid intensification record

By: JeffMasters, 1:54 PM GMT on October 12, 2010

Hurricane warnings are flying along the coast of Mexico's Yucatan Peninsula for Hurricane Paula, the 16th named storm and 9th hurricane of this very active 2010 Atlantic hurricane season. Paula intensified remarkably quickly, setting a modern record for the fastest intensification from the issuance of the first advisory to hurricane strength. The first advisory for Paula was issued at 5pm EDT yesterday, and Paula strengthened into a hurricane just twelve hours later, at 5am EDT this morning. Since reliable record keeping of intensification rates of Atlantic hurricanes began in 1970, when regular satellite coverage became available, no storm has ever intensified into a hurricane that quickly. Hurricane Humberto of 2007 held the previous record for fastest intensification from first advisory issued to hurricane strength--18 hours. However, there is one caveat to keep in mind. The final Atlantic hurricane data base (HURDAT) stores points every six hours--at 00, 06, 12, and 18 UTC. It is likely that Paula will be recognized as having been a tropical depression at 12 UTC (8am EDT) or 18Z (2pm EDT) yesterday, 3 - 9 hours before the first advisory was issued. Even though Paula met the criteria for being named a tropical depression yesterday morning, NHC elected not to do so, since it was unclear whether or not passage over land would disrupt the nascent tropical depression (a new tropical depression must demonstrate some staying power before it will get recognized, typically.) In the final HURDAT data base, it may turn out that Paula will be recognized as intensifying from first advisory to a hurricane in eighteen hours, tying Humberto's record. There have been six storms that accomplished the feat in 24 hours.


Figure 1. Microwave image of Paula taken at 6:35am EDT 10/12/10 shows that Paula is a small hurricane, with heavy rains confined to a small area near the center. Though the images are not radar images, one can think of these images as similar to having a radar in space that can provide images of where heavy rain is occurring. Image credit: Navy Research Lab, Monterey.

Fortunately for Mexico, Paula has not been able to maintain its rapid intensification rate. Satellite intensity estimates show that Paula has leveled off in intensity this morning. Microwave satellite images (Figure 1) and traditional satellite imagery reveal that Paula is small hurricane with a limited amount of heavy thunderstorms. Water vapor satellite loops indicate that the atmosphere in the Western Caribbean is moist enough to support further development, but moderate wind shear of 15 knots due to strong upper-level winds out of the south are hampering Paula's intensification. Radar from Belize and Cancun shows that Paula's outer spiral bands are still well offshore. The next hurricane hunter mission is scheduled for 2pm EDT this afternoon; there has been no airplane in the storm since about 4am this morning.


Figure 2. Total accumulated rainfall for the 5.25 day period beginning at 2am EDT today, October 12, 2010, as predicted by the 2am EDT runs of the HWRF model (top) and GFDL model (bottom.) The HWRF model predicts Paula will stay trapped in the Western Caribbean, causing very high rainfall totals. Image credit: Morris Bender, NOAA/GFDL.

Forecast for Paula
Tropical storm force winds of 39+ mph extend out from Paula's center about 60 miles to the north, and are forecast to expand to 100 miles by early Wednesday morning. Paula's current northwest motion of 10 mph means that tropical storm force winds should reach the coast of Mexico near Cozumel between 8pm - 2am local time tonight. A good way to visualize this is to use our wundermap with the "hurricane" layer turned on, and click on the "forecast" and "wind radius" boxes. Hurricane force winds extend out just ten miles from the center, so only a very small region of coast will receive Paula's strongest winds. The 5am EDT wind probability product from NHC predicts a 91% chance that Cozumel will receive tropical storm force winds, and a 31% chance of getting hurricane force winds of 74+ mph. The main threat from the storm will be heavy rain, particularly over western Cuba and the northeastern tip of Mexico's Yucatan Peninsula, if Paula stalls as expected and wanders in the region for many days. Rainfall forecasts from the HWRF and GFDL models (Figure 2) suggest that Paula will be capable of dumping more than a foot of rain in isolated regions over the next five days. The latest SHIPS model forecast calls for wind shear to rise to the high range, 20 - 25 knots, tonight through the end of the week. This high shear, combined with the dry atmosphere to the north of Paula, should keep the hurricane from becoming a major hurricane. NHC is giving Paula just a 6% chance of becoming a major hurricane. The shear and dry air may even weaken the storm below hurricane strength later this week, as suggested by most of the intensity forecast models. Paula is a small storm, so is fairly vulnerable to shear and dry air.

There is considerable doubt about the future path of Paula. Steering currents in the Western Caribbean will collapse on Wednesday, potentially allowing Paula to wander in the region for many days, as predicted by the GFS and HWRF models. It is also possible that Paula will push far enough inland over Mexico's Yucatan Peninsula that the storm will dissipate. Finally, if Paula grows large enough and strong enough, it could get caught up a strong trough of low pressure predicted to traverse the U.S. this week (and spawn a Nor'easter for New England this weekend.) In this scenario, offered by the GFDL model, Paula would make a sharp turn to the east-northeast, hit western Cuba, bring tropical storm-force finds to the Florida Keys on Friday, then move into the Bahama Islands by Saturday morning. NHC is making the reasonable forecast of sticking with what the majority of models are saying, but residents of South Florida, Central Cuba, and the Bahamas should be prepared for Paula to come their way as a strong tropical storm.

"Hurricane Haven" airing this afternoon
My live Internet radio show, "Hurricane Haven", will be airing again today at 4pm EDT. The call in number is 415-983-2634, or you can post a question to broadcast@wunderground.com. Be sure to include "Hurricane Haven question" in the subject line.

Today's show will be about 30 minutes, and you can tune in at http://www.wunderground.com/wxradio/wubroadcast.h tml. The show will be recorded and stored as a podcast.

Jeff Masters

Hurricane

Updated: 6:35 PM GMT on January 03, 2012

Permalink

Tropical Storm Paula forming

By: JeffMasters, 7:30 PM GMT on October 11, 2010

Data from the Hurricane Hunters, land stations, and satellite imagery reveal that the strong tropical disturbance centered near the coast of Honduras just west of the border with Nicaragua is now Tropical Storm Paula. Paula is the 16th named storm of the 2010 Atlantic hurricane season. The Hurricane Hunters reported a central pressure of 1001 mb and top surface winds of 45 mph in their 2:11pm EDT center fix. Satellite imagery shows a well-organized system with a modest but increasing amount of intense thunderstorm activity, and some respectable low-level spiral bands. Water vapor satellite loops reveal that Paula has been able to substantially moisten the atmosphere in the Western Caribbean over the past day, and dry air will be less of an impediment to development than it was yesterday. Wind shear is a moderate 10 - 15 knots. Puerto Lempira, Honduras reported sustained winds of 35 mph at 12pm CST this afternoon, with 3.31" of rain from the storm thus far.


Figure 1. Afternoon satellite image of Paula.

Forecast for Paula
Proximity to land is hampering Paula's ability to intensify some, and the storm's northwest movement of 10 mph will take the center far enough away from the coast of Honduras this evening to substantially increase the storm's ability to intensify. The latest SHIPS model forecast calls for wind shear to stay mostly in the moderate range, 10 - 15 knots, through Tuesday afternoon, then increase to the high range, 20 - 25 knots, for the remainder of the week. The computer models predict Paula will continue on a northwest motion then turn more north-northwest on Wednesday, which would take the storm close to landfall on the coast of Belize or Mexico's Yucatan Peninsula Tuesday night or Wednesday morning. At that time, Paula may be approaching Category 2 hurricane status, due to the moderate wind shear, SSTs of 29°C, and a sufficiently moist atmosphere. On Wednesday, there is considerable doubt about the future path of Paula. Steering currents in the Western Caribbean will collapse, potentially allowing Paula to wander in the region for many days, as predicted by the GFS and HWRF models. It is also possible that Paula will push far enough inland over Mexico's Yucatan Peninsula that the storm will dissipate, as predicted by the NOGAPS model. Finally, if Paula grows strong quickly, and pushes far enough north, it could get caught up a strong trough of low pressure predicted to traverse the U.S. this week (and spawn a Nor'easter for New England this weekend.) In this scenario, offered by the GFDL model, Paula would make a sharp turn to the east-northeast, hit western Cuba, bring tropical storm-force finds to the Florida Keys on Thursday, then move into the Bahama Islands by Friday or Saturday. It is too early to say which of these scenarios is the most likely, as the storm is just forming and the models do not have a good handle on it yet. Regardless, northern Honduras, Belize, and Mexico's Yucatan Peninsula will receive dangerous flooding rains from Paula today through Wednesday.

The U.S. drought in major hurricanes
On average, the U.S. gets hit by one major Category 3 or stronger hurricane every two years. This year, the team of hurricane forecasters at Colorado State University called for a 76% chance of a major hurricane hitting the U.S. in their June forecast. However, the odds of a major hurricane hitting the U.S. are rapidly dwindling. Over the past fifty years, the only Category 3 or stronger hurricanes to hit the U.S. after October 1 were Hilda (October 3, 1964), Opal (October 4, 1995), and Wilma (October 24, 2005). Hilda and Opal were already named tropical storms as of October 1, so Wilma was the major hurricane that formed after October 1 to hit the U.S. during this period. Although we still need to keep a wary eye on developments in the Western Caribbean over the next few weeks, the odds are that 2010 will join 1951 as the only year to have five or more major hurricanes in the Atlantic, but no landfalling major hurricane in the U.S. (1958 is also listed as such a year, but a re-analysis effort is showing that Hurricane Helene hit North Carolina as a major hurricane that year.) If 2010 finishes without a major hurricane hitting the U.S., this will mark the first such five-year stretch since 1910 - 1914.


Figure 2. Hurricane Wilma over South Florida as a Category 3 hurricane on October 24, 2005. Wilma was the last major hurricane to hit the U.S.

However, some caveats are required. Hurricanes Gustav and Ike, which both made landfall in the U.S. in 2008 as top-end Category 2 storms with 110 mph winds, would probably have been classified as Category 3 hurricanes had they occurred early in the 20th century. This is because in past, when there were not any reliable wind measurements in the vicinity of a landfalling hurricane (a common occurrence), the storm was classified based on its central pressure. Gustav and Ike had central pressures of 957 and 952 mb, respectively, which would have qualified them as Category 3 storms. Similarly, Hurricane Floyd of 1999 and Hurricane Isabel of 2002 (though not within the last five years) were strong Category 2 hurricanes with 105 mph winds at landfall, but had central pressures of 956 mb. These hurricanes would also have been classified as Category 3 hurricanes in the past. There are many storms from the 1930s, 1940s, and 1950s that will likely change their landfall classification once re-analysis efforts are completed over the next few years. One case is Hurricane Ten of 1949, which is listed as having winds of a low-end Category 4 hurricane (135 mph) just before landfall, which would make it the only October major hurricane to make landfall in Texas. However, the hurricane is only given a Category 2 strength at landfall, based on its central pressure.

Prior to 1960, there were five major hurricanes that hit Florida in October. Most notable of these is Hurricane King, which hit downtown Miami on October 18, 1950, as a Category 3 hurricane.

Record quiet hurricane and typhoon seasons in the Pacific
Over in the Western Pacific, it is currently the quietest typhoon season on record, according to statistics computed by forecaster Paul Stanko at the NWS office on Guam. On average, by this point in the season, there should have been 21 named storms, 13 typhoons, and 3 supertyphoons (storms with 150+ mph winds.) So far in 2010, there have been just 12 named storms, 6 typhoons, and no supertyphoons. The record lows for the Western Pacific (since 1951) are 18 named storms, 9 typhoons, and 0 supertyphoons. We have a good chance of beating or tying all of those records. Over the in the Eastern Pacific, it has also been a near record-quiet season. On average, the Eastern Pacific has 15 named storms, 8 hurricanes, and 3 intense hurricanes in a season. So far in 2010, there have been 7 named storms, 3 hurricanes, and 2 intense hurricanes. The record quietest season since 1966 was the year 1977, when the Eastern Pacific had 8 named storms, 4 hurricanes, and 0 intense hurricanes. Climatology suggests that on average, we can expect just one more named storm in the Eastern Pacific this late in the season, so there is a good chance that the 2010 season is over. La Niña is largely responsible to the quiet Eastern Pacific hurricane season, due in part to the cool sea surface temperatures it brought. La Niña also commonly causes less active Western Pacific typhoon seasons, since the warmest waters there shift closer to Asia, reducing the amount of time storms have over water.

I'll have an update Tuesday morning at the latest.

Jeff Masters

Hurricane

Updated: 1:04 PM GMT on November 16, 2010

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98L well-organized; a 5-year drought in U.S. major hurricanes

By: JeffMasters, 1:27 PM GMT on October 11, 2010

A strong tropical disturbance (98L) is centered near the northeastern coast of Honduras along the border with Nicaragua. This system is close to tropical depression status, but development is currently being hampered by the storm's proximity to land. Satellite imagery shows a well-organized system with plenty of spin, a modest amount of intense thunderstorm activity, and some respectable low-level spiral bands. Water vapor satellite loops reveal that 98L has been able to substantially moisten the atmosphere in the Western Caribbean over the past day, and dry air will be less of an impediment to development than it was yesterday. Wind shear is a moderate 10 - 15 knots.


Figure 1. NASA MODIS satellite image of 98L taken 12:35pm EDT Sunday October 10, 2010. Image credit: NASA.

Forecast for 98L
The west-northwest to northwest movement of 98L at 10 mph should take the center far enough away from the coast of Honduras this evening to substantially increase the storm's odds of development. The latest SHIPS model forecast calls for wind shear to stay mostly in the moderate range, 10 - 15 knots, through Tuesday afternoon, then increase to the high range, above 20 knots, for the remainder of the week. NHC is calling for a 60% chance of 98L becoming a tropical depression by Wednesday morning; I'd put these odds higher, at 70%. The computer models predict 98L will continue on a west-northwest to northwest motion through Tuesday, which would take the storm close to the coast of Belize/Mexico's Yucatan Peninsula by Tuesday night. At that point, it is possible that a trough of low pressure over the eastern U.S. will reach far enough south to pull 98L to the northeast across western Cuba and the Florida Keys by Thursday, as predicted by the latest 8pm EDT (0Z) run of the GFDL model. Two other models, the GFS and HWRF models, keep the storm confined to the Western Caribbean for the rest of the week, though. The ECMWF, NOGAPS, and UKMET models do not develop 98L into a tropical depression. In any case, Honduras, northeastern Nicaragua, and the Cayman Islands can expect heavy rain from 98L over the next three days. Heavy rains from 98L will begin to affect Belize and Mexico's Yucatan Peninsula on Tuesday, and perhaps northern Guatemala and the western half of Cuba as well. These rains may potentially last many days and cause significant flooding problems.

The U.S. drought in major hurricanes
On average, the U.S. gets hit by one major Category 3 or stronger hurricane every two years. This year, the team of hurricane forecasters at Colorado State University called for a 76% chance of a major hurricane hitting the U.S. in their June forecast. However, the odds of a major hurricane hitting the U.S. are rapidly dwindling. Over the past fifty years, the only Category 3 or stronger hurricanes to hit the U.S. after October 1 were Hilda (October 3, 1964), Opal (October 4, 1995), and Wilma (October 24, 2005). Hilda and Opal were already named tropical storms as of October 1, so Wilma was the major hurricane that formed after October 1 to hit the U.S. during this period. Although we still need to keep a wary eye on developments in the Western Caribbean over the next few weeks, the odds are that 2010 will join 1951 as the only year to have five or more major hurricanes in the Atlantic, but no landfalling major hurricane in the U.S. (1958 is also listed as such a year, but a re-analysis effort is showing that Hurricane Helene hit North Carolina as a major hurricane that year.) If 2010 finishes without a major hurricane hitting the U.S., this will mark the first such five-year stretch since 1910 - 1914.


Figure 2. Hurricane Wilma over South Florida as a Category 3 hurricane on October 24, 2005. Wilma was the last major hurricane to hit the U.S.

However, some caveats are required. Hurricanes Gustav and Ike, which both made landfall in the U.S. in 2008 as top-end Category 2 storms with 110 mph winds, would probably have been classified as Category 3 hurricanes had they occurred early in the 20th century. This is because in past, when there were not any reliable wind measurements in the vicinity of a landfalling hurricane (a common occurrence), the storm was classified based on its central pressure. Gustav and Ike had central pressures of 957 and 952 mb, respectively, which would have qualified them as Category 3 storms. Similarly, Hurricane Floyd of 1999 and Hurricane Isabel of 2002 (though not within the last five years) were strong Category 2 hurricanes with 105 mph winds at landfall, but had central pressures of 956 mb. These hurricanes would also have been classified as Category 3 hurricanes in the past. There are many storms from the 1930s, 1940s, and 1950s that will likely change their landfall classification once re-analysis efforts are completed over the next few years. One case is Hurricane Ten of 1949, which is listed as having winds of a low-end Category 4 hurricane (135 mph) just before landfall, which would make it the only October major hurricane to make landfall in Texas. However, the hurricane is only given a Category 2 strength at landfall, based on its central pressure.

Prior to 1960, there were five major hurricanes that hit Florida in October. Most notable of these is Hurricane King, which hit downtown Miami on October 18, 1950, as a Category 3 hurricane.

Record quiet hurricane and typhoon seasons in the Pacific
Over in the Western Pacific, it is currently the quietest typhoon season on record, according to statistics computed by forecaster Paul Stanko at the NWS office on Guam. On average, by this point in the season, there should have been 21 named storms, 13 typhoons, and 3 supertyphoons (storms with 150+ mph winds.) So far in 2010, there have been just 12 named storms, 6 typhoons, and no supertyphoons. The record lows for the Western Pacific (since 1951) are 18 named storms, 9 typhoons, and 0 supertyphoons. We have a good chance of beating or tying all of those records. Over the in the Eastern Pacific, it has also been a near record-quiet season. On average, the Eastern Pacific has 15 named storms, 8 hurricanes, and 3 intense hurricanes in a season. So far in 2010, there have been 8 named storms, 3 hurricanes, and 2 intense hurricanes. The record quietest season since 1966 was the year 1977, when the Eastern Pacific had 8 named storms, 4 hurricanes, and 0 intense hurricanes. Climatology suggests that on average, we can expect just one more named storm in the Eastern Pacific this late in the season, so there is a good chance that the 2010 season is over. La Niña is largely responsible to the quiet Eastern Pacific hurricane season, due in part to the cool sea surface temperatures it brought. La Niña also commonly causes less active Western Pacific typhoon seasons, since the warmest waters there shift closer to Asia, reducing the amount of time storms have over water.

I'll have an update Tuesday morning at the latest.

Jeff Masters

Hurricane

Updated: 8:27 PM GMT on August 17, 2011

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Western Caribbean disturbance 98L still a threat to develop

By: JeffMasters, 5:24 PM GMT on October 10, 2010

An area of disturbed weather (98L) in the Western Caribbean, a few hundred miles east of the coast of Nicaragua, has the potential to become a tropical depression at any time today or Monday as it moves northwestwards toward the Nicaragua/Honduras border at 5 - 10 mph. The disturbance has quite a bit of spin, but an organized surface circulation is not yet apparent on satellite images. Colombia's San Andres Island, to the southwest of 98L's center, is reporting northwest winds, suggesting that 98L may be close to having a closed surface circulation. An a href=http://manati.orbit.nesdis.noaa.gov/ascat_ima ges/cur_50km/zooms/WMBds20.pngASCAT pass from 10:41am EDT this morning confirms that 98L does not have a closed circulation, but it is almost there.Satellite imagery shows a relatively meager amount of intense thunderstorms associated with 98L, and pressures at nearby land stations are falling slowly or not at all. Water vapor satellite loops reveal that considerable dry air surrounds 98L, and this dry air is interfering with development. The Hurricane Hunters are on call to investigate 98L on Monday afternoon.


Figure 1. Afternoon satellite image of 98L.

Forecast for 98L
98L is likely to bring heavy rains to northeastern Honduras and Nicaragua on Sunday and Monday, and to Belize and Mexico's Yucatan Peninsula on Tuesday. Intermittent heavy rains will also affect the Cayman Islands, Jamaica, and Western Cuba over the next three days. The latest SHIPS model forecast calls for wind shear to stay mostly in the moderate range, 10 - 15 knots, through Tuesday. This should allow 98L to reach tropical depression status at any time, and NHC is calling for a 60% chance of 98L becoming a tropical depression by Tuesday morning. The computer models predict 98L will continue on a west-northwest to northwest motion through Tuesday, which would take the storm close to the coast of Belize/Mexico's Yucatan Peninsula by Tuesday. At that point, it is possible that a trough of low pressure over the eastern U.S. will reach far enough south to pull 98L to the northeast across Cuba. None of computer models available as of 1pm EDT developed 98L into a tropical depression. I don't believe 98L will become a depression today, but expect that it will be one by Tuesday.

I'll have an update Monday morning.

Jeff Masters

Hurricane

Updated: 6:36 PM GMT on January 03, 2012

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Western Caribbean disturbance 98L a threat to develop; Otto weakening

By: JeffMasters, 1:48 PM GMT on October 09, 2010

An area of disturbed weather (98L) is in the Western Caribbean, a few hundred miles east of the coast of Nicaragua. The disturbance has a modest and slowly increasing amount of intense thunderstorms, and is showing some spin. The disturbance is drifting northwest at less than 5 mph, and is under a moderate 15 knots of wind shear. Dry air in the Western Caribbean has been interfering with development, but 98L is now generating enough thunderstorms that the environment in the Western Caribbean is moistening, which will support further development. Pressures at Colombia's San Andres Island near the center of 98L are not falling, and satellite imagery show disturbed weather only over a very modest portion of the Caribbean, so any development today will be slow to occur.


Figure 1. Morning satellite image of 98L.

Forecast for 98L
98L is likely to bring heavy rains to northeastern Honduras and Nicaragua on Sunday, and possibly the Cayman Islands and Jamaica as well. The latest SHIPS model forecast calls for wind shear to stay in the moderate range, 10 - 20 knots, through Tuesday. This should allow 98L to reach tropical depression status early next week, though NHC is only calling for a 20% chance of 98L becoming a tropical depression by Monday morning. The GFDL and HWRF models are the most aggressive developing 98L. These models predict 98L will intensify into Tropical Storm Paula by Monday, move northwest and then north, and pass through the Cayman Islands on Monday night and Tuesday morning as a tropical storm. Paula would then hit western or central Cuba as a hurricane on Tuesday or Wednesday, brush the Florida Keys, then accelerate northeastward through the western Bahamas on Wednesday or Thursday. This is probably too aggressive of a forecast, given 98L's current small size and lack of organization. The UKMET model also develops 98L, but keeps the storm in the Western Caribbean over the next seven days. The NOGAPS model keeps 98L weak and predicts a more west-northwesterly motion into Mexico's Yucatan Peninsula on Wednesday. The GFS and ECMWF models do not develop 98L. One argument against the development of 98L would be that the phase of the Madden-Julian Oscillation is currently promoting sinking, stable air over the Western Caribbean, which tends to make the atmosphere dryer and more stable. However, I think that 98L will spend enough time in the Western Caribbean to overcome the relatively stable, dry air, and become a tropical depression or tropical storm by Tuesday. The likelihood of the storm hitting Cuba versus moving more to the west-northwest and hitting Mexico's Yucatan Peninsula is difficult to call at this point.

Otto weakening, pulling away from the the islands
The deluge has finally ended for Puerto Rico, the Virgin Islands, and the northern Lesser Antilles Islands from Hurricane Otto. This is welcome news in St. Thomas in the U.S. Virgin Islands, where Otto and its precursor storminess dumped 15.25" of rain over the past eight days. On average, St.Thomas expects to receive just 1.44" of rain during the first eight days of October. Satellite imagery shows that Otto is beginning to suffer the ill-effects of high wind shear of 20 - 30 knots. The cloud pattern has become distorted and non-symmetric, with the clouds on the southwest side of the storm being eaten away by the strong upper-level winds from the southwest creating the shear. Otto will continue to deteriorate due to increasing wind shear until the storm transitions into an extratropical storm on Monday.


Figure 2. Satellite image of Otto taken by NASA's MODIS instrument on their Terra satellite at 11:05 am EDT October 8, 2010. Image credit: NASA.


A challenge to the validity of the world extreme heat record of 136.4°F (58°C) at Al Aziza, Libya
One of the "sacred cows" of world weather extremes has been the widely reported "hottest temperature ever recorded on earth", a reading of 58°C (136.4°F) reported from Al Azizia, Libya on Sept. 13, 1922. In a remarkable piece of research, our featured Weather Extremes blogger Christopher C. Burt concludes: the temperature observations at Al Azizia prior to 1927 (when the site and instruments were changed) are obviously invalid. The shelter housing the thermometer was most likely over exposed and measuring heat radiating of off the black-tarred concrete of the terrace on which it was placed.

Has Mr. Burt slain one of meteorology's most sacred cows? You be the judge. Check out the full story at his blog.

I'll have an update Sunday by 2pm EDT.

Jeff Masters

Hurricane

Updated: 1:49 PM GMT on October 09, 2010

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Hurricane Otto's deluge continues; world extreme heat record of 136.4°F bogus?

By: JeffMasters, 2:51 PM GMT on October 08, 2010

The deluge continues over Puerto Rico, the Virgin Islands, and the northern Lesser Antilles Islands from Hurricane Otto, which is bringing a fourth straight day of heavy rains. Otto is the eighth hurricane of this very active 2010 hurricane season; our tally now stands at 15 named storms, 8 hurricanes, and 5 intense hurricanes. An average season has 10 - 11 named storms, 6 hurricanes, and 2 intense hurricanes. Otto's rains have caused a fair degree of trouble in the islands. According to Wikipedia, Heavy downpours in the U.S. Virgin Islands caused flooding across several local roads. In Saint Croix, a roadway section leading into Enfield Green collapsed on the night of October 6, temporarily cutting the south-side neighborhood off to vehicle traffic until a makeshift roadway through Carlton Estate was created the next day. On the island's North Shore in La Vallee, landslides and localized flooding in low-lying areas created some issues. There were no reports of major damage, however, and the roads remained passable. Torrential floods across the British Virgin Islands toppled several cars and caused extensive damage to utility lines and drainage pipes; dozens of people (mostly in Road Town) were left without power and water. An estimated 100 homes were flooded in Saint Lucia, and a fishing village on the island's east coast was declared a disaster zone. Schools, businesses and government offices across all of the Virgin Islands and in Saint Kitts and Nevis were closed until further notice.

In Puerto Rico, heavy rainfalls fell across the municipality of Utuado on October 7. As a result, a road to a neighborhood was made inaccessible after being severely damaged by gushing waters when parts of the Arecibo River overflowed. That same day, a landslide dragged away a communication post along the road and made it impossible for larger vehicles--including ambulances--to access the site. Meanwhile, fourteen families in the municipality of Ponce were cut off from communication because of several landslides. A residence alongside a road suffered significant damage and its inhabitants were forced to evacuate. Furthermore, a district in Cayey was isolated after a bridge collapsed, while burst riverbanks caused flooding across streets, trapping dozens of families in their homes. Across the island, 40 roads were closed due to torrential rainfall, and 19 streets had at least one lane closed.



Figure 1. Morning satellite image of Otto.

Weather radar out of Puerto Rico shows that a large area of heavy rain will continue to affect the Virgin Islands and Puerto Rico today, and flash flood warnings are posted on these islands through tonight. Martinique radar shows considerably less activity over the Lesser Antilles.

Satellite imagery shows a well-organized storm with an expanding Central Dense Overcast (CDO) of high cirrus clouds covering the center. Infrared satellite imagery shows a region of intense thunderstorms with very cold cloud tops, with the suggestion of a warm spot--an eye--forming. Otto should continue to intensify until Saturday morning, when wind shear will quickly rise to a very high 30+ knots.


Figure 2. Radar-estimated rainfall from Otto over Puerto Rico and the Virgin Islands this week shows that rains in excess of eight inches (white colors) have fallen in many regions. The strange ray-like pattern to the east of the radar location (the white "+" symbol) is due to mountains blocking the radar beam.

Western Caribbean disturbance
An area of disturbed weather in the Western Caribbean, a few hundred miles east of the coast of Nicaragua, has only a small amount of intense thunderstorms, but is showing some spin. The disturbance is nearly stationary, and is under a moderate 15 - 20 knots of wind shear. Some dry air in the Western Caribbean is interfering with development. I expect the storm will begin to build some significant heavy thunderstorms over the weekend, bringing heavy rains to northeastern Honduras and Nicaragua. None of the models develop the disturbance into a tropical depression, but it does have some potential for slow development over the next few days, and NHC is giving the disturbance a 20% chance of developing into a tropical depression by Sunday. The ECMWF model has the disturbance drifting northward next week and crossing Central Cuba on Wednesday or Thursday. Most of the other models keep the storms confined to the Caribbean.

A challenge to the validity of the world extreme heat record of 136.4°F (58°C) at Al Aziza, Libya
One of the "sacred cows" of world weather extremes has been the widely reported "hottest temperature ever recorded on earth", a reading of 58°C (136.4°F) reported from Al Azizia, Libya on Sept. 13, 1922. In a remarkable piece of research, our featured Weather Extremes blogger Christopher C. Burt concludes: the temperature observations at Al Azizia prior to 1927 (when the site and instruments were changed) are obviously invalid. The shelter housing the thermometer was most likely over exposed and measuring heat radiating of off the black-tarred concrete of the terrace on which it was placed.

Has Mr. Burt slain one of meteorology's most sacred cows? You be the judge. Check out the full story at his blog.

Jeff Masters

Hurricane

Updated: 6:36 PM GMT on January 03, 2012

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Otto transitioning to a tropical storm

By: JeffMasters, 1:35 PM GMT on October 07, 2010

Subtropical Storm Otto, the 15th named storm of this very busy 2010 Atlantic hurricane season, is here. Otto is not a threat to bring high winds to any land areas, but will produce heavy rains over Puerto Rico, the Virgin Islands, and northern Lesser Antilles. Radar estimated rainfall over Puerto Rico and the Virgin Islands (Figure 2) shows rainfall amounts in excess of eight inches have fallen in several locations over the past three days, and the St. Thomas Airport officially recorded 9.30" of rain so far from Otto. Not surprisingly, Flash Flood Warnings are posted for both the Virgin Islands and Puerto Rico. Weather radar out of Puerto Rico shows that a large area of heavy rain will continue to affect the Virgin Islands and eastern Puerto Rico today. Martinique radar shows considerably less activity over the Lesser Antilles.


Figure 1. NASA MODIS image of Subtropical Storm Otto taken at 12:55pm EDT October 6, 2010.

Satellite loops show Otto's heaviest thunderstorms lie in two bands to the south, many hundreds of miles from the storm's center. This is characteristic of a subtropical storm, which is a hybrid between a tropical storm and an extratropical storm. An upper level low pressure system over Otto has pumped cold, dry air aloft into the storm, keeping it from being fully tropical. However, the upper low is weakening, and Otto has recently developed a burst of heavy thunderstorms near its center, and very tropical storm-like spiral bands are now developing to the east and south of Otto's center. Otto is fast becoming fully tropical, and will be called Tropical Storm Otto later today. The storm's newly developing spiral bands will mostly stay offshore, but a few heavy rain showers capable of dumping 1 - 2 inches of rain may affect the Turks and Caicos Islands today, as well as the northern Dominican Republic. The heavier rains in Otto's old rain band over Puerto Rico and the Virgin Islands will continue to dump flooding rains in those locations through tonight. Steering currents favor Otto being lifted northwards and then northeastwards out to sea by Friday. Given the very warm waters of 28 - 29°C and low wind shear of 5 - 10 knots today, Otto may approach hurricane strength before high wind shear in excess of 20 knots impacts the storm Friday night.


Figure 1. Radar-estimated rainfall from Tropical Storm Otto over Puerto Rico and the Virgin Islands shows that rains in excess of eight inches (white colors) have fallen in many regions. The strange ray-like pattern to the east of the radar location (the white "+" symbol) is due to mountains blocking the radar beam.

Elsewhere in the tropics
An area of disturbed weather has formed in the Western Caribbean, a few hundred miles west of Jamaica. The disturbance has a moderate area of intense thunderstorms that brought close to two inches of rain to Grand Cayman Island over the past day. The disturbance is under a high 15 - 25 knots of wind shear, and is not likely to develop significantly today. The disturbance is headed south at 10 - 15 mph, and will bring heavy rains to northeastern Honduras and Nicaragua over the next two days. None of the models develop the disturbance, but it does have some potential for slow development beginning on Friday when it will be off the coast of Nicaragua, in a region of lower wind shear and higher moisture. NHC is giving the disturbance a 10% chance of developing into a tropical depression by Saturday.

Monsoon flooding kills 139 in Asia
Heavy monsoon rains triggered flash flooding in a remote section of Indonesia this week that killed at least 91 people and left 100 more missing. In Vietnam, heavy rains of up to 51" (1300 mm) have fallen since Friday, resulting in river flooding that killed at least 48 people, with 23 people still missing. Over 34,000 people are homeless from the floods, which hit five provinces from Nghe An to Thua Thien-Hue, a swath of territory starting some 300 km (180 miles) south of Hanoi and stretching south. Heavy monsoon rains of up to seven inches over the past week have also hit nearby Hainen Island in China. The resulting flooding was the worst in 50 years there, and killed one person and forced the evacuation of 55 villages with 213,000 people.

Press
I've been a subscriber for several years to NewScientist magazine, a weekly science news magazine that does a great job staying abreast of all the latest breaking science happenings. This week's October 4 issue features a 4-page section on Extreme Weather that I wrote for them as part of their "Instant Expert" series. If you haven't ever seen the magazine, I enthusiastically recommend taking a look.

If you're a fan of the geek humor xkcd webcomic, see if you can find me on the hilarious map of the "blogosphere" on comic artist Randall Munroe's latest xkcd comic. I like the disparity between my influence in September vs. March, but thought I should have been closer to the "Bay of Flame!" I also appeared in a mouse "rollover" text box in an xkcd comic during the Gulf oil disaster earlier this year.

Jeff Masters

Hurricane

Updated: 6:36 PM GMT on January 03, 2012

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Subtropical Depression 17 forms; monsoon rains kill over 100 in Asia

By: JeffMasters, 1:04 PM GMT on October 06, 2010

Subtropical Depression Seventeen formed this morning, approximately 200 miles north of Puerto Rico. The storm is not a threat to bring high winds to any land areas, but will produce heavy rains over Puerto Rico, the Virgin Islands, the northern Lesser Antilles, and perhaps the eastern Dominican Republic. Radar estimated rainfall over Puerto Rico and the Virgin Islands (Figure 1) shows rainfall amounts in excess of eight inches have fallen near St. Thomas in the Virgin Islands, and the St. Thomas Airport officially measured 6.61" yesterday--its 5th wettest day in history. St. Thomas has picked up an additional 1.48" today as of 9am AST. Not surprisingly, Flash Flood Warnings are posted for the island. Weather radar out of Puerto Rico shows that a large area of heavy rain will continue to affect the Virgin Islands and eastern Puerto Rico this morning. Martinique radar shows somewhat less activity over the Lesser Antilles.

Satellite loops show STD 17 has a broad, somewhat ill-defined center of circulation, with the heaviest thunderstorms 50 or so miles from the center. This is characteristic of a subtropical storm, which is a hybrid between a tropical storm and an extratropical storm. An upper level low pressure system to the west of STD 17 has pumped cold, dry air aloft into STD 17, keeping it from being fully tropical. As the trough gradually weakens today and Thursday, STD 17 should become fully tropical and intensify into Tropical Storm Otto. Steering currents favor Otto being lifted northwards and then northeastwards out to sea by Friday.


Figure 1. Radar-estimated rainfall from Subtropical Depression Seventeen over Puerto Rico and the Virgin Islands shows that rains in excess of eight inches (white colors) have fallen near St. Thomas.

Elsewhere in the tropics
Most of the models indicate the possibility that a strong tropical disturbance or tropical depression forming in the Southern Caribbean, off the coast of Nicaragua, 5 - 7 days from now.

Monsoon flooding kills 83 in Indonesia, 28 in Vietnam
Heavy monsoon rains triggered flash flooding in a remote section of Indonesia this week that killed at least 83 people. Another 68 people are missing, and 3,000 homeless. In Vietnam, heavy rains of up to 51" (1300 mm) have fallen since Friday, resulting in river flooding that killed at least 28 people. Over 34,000 people are homeless from the floods, which hit five provinces from Nghe An to Thua Thien-Hue, a swath of territory starting some 300 km (180 miles) south of Hanoi and stretching south. Heavy monsoon rains also hit nearby Hainen Island in China, forcing the evacuation of 64,000 people.

Jeff Masters

Hurricane

Updated: 6:37 PM GMT on January 03, 2012

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97L more organized, could be a tropical depression by Wednesday

By: JeffMasters, 12:55 PM GMT on October 05, 2010

A large region of disturbed weather (Invest 97L) is bringing heavy rain showers and strong wind gusts to the Lesser Antilles Islands and waters near Puerto Rico, the Virgin Islands, and the Dominican Republic. At 8:30am AST this morning, Charlotte Amalie in the Virgin Islands recorded a wind gust of 52 mph in a heavy rain squall. Long range radar out of Puerto Rico shows that the echoes associated with 97L are slowly growing more organized, and now have a broad circulation, centered just north of the Virgin Islands. This broad circulation is also suggested by recent visible satellite loops. Satellite imagery also shows that low-level spiral bands are slowly developing over the northern Lesser Antilles islands, to the east of the center of circulation. Martinique radar shows a modest amount of heavy thunderstorm activity over the Lesser Antilles, and rainfall amounts of 1 - 3 inches have been common in the islands over the past two days. An upper level trough of low pressure is contributing to the heavy rain showers by making the atmosphere more unstable. This same trough is also bringing moderate wind shear of 10 - 15 knots and pumping dry air into the west side of 97L. These impacts should keep 97L from developing into a tropical depression today.


Figure 1. Morning satellite image of Invest 97L.

Forecast for 97L
Tonight and Wednesday morning, the upper-level trough to 97L's west is forecast to weaken. This will significantly reduce the amount of dry and and wind shear affecting the storm, and 97L should be able to organize into a tropical depression by Wednesday afternoon, when the Hurricane Hunters are scheduled to pay their first visit. The SHIPS model predicts that wind shear over 97L will fall to the low range, 5 - 10 knots, by Wednesday. The current northwest motion of 97L should keeps its center from crossing Hispaniola. All of the major computer models show development of 97L into a tropical depression by Wednesday night, just north or northeast of Hispaniola. By Thursday, a passing trough of low pressure is expected to pull 97L to the northeast away from Hispaniola, and rains should end by Friday on the island. NHC is giving 97L a 60% chance of developing into a tropical depression by Thursday. Since the center of this potential Tropical Storm Otto is not expected to pass over any land areas, rainfall will be the primary threat. The Dominican Republic and Puerto Rico are most at risk of flooding rains from the storm, which could bring 3 - 6 inches of rain through Thursday. Haiti and the Turks and Caicos Islands are at less risk, since the dry air and lingering wind shear from the upper-level trough to 97L's west will keep heavy thunderstorm development lower on the west side of the storm. Flash flood watches are posted for the Virgin Islands and Puerto Rico for today through Wednesday, and heavy rains will continue in the northern Lesser Antilles Islands through Wednesday.

Elsewhere in the tropics
Most of the models indicate the possibility that a strong tropical disturbance or tropical depression forming in the Southern Caribbean, off the coast of Nicaragua, 6 - 7 days from now.

"Hurricane Haven" airing this afternoon
My live Internet radio show, "Hurricane Haven", will be airing again today at 4pm EDT. The call in number is 415-983-2634, or you can post a question to broadcast@wunderground.com. Be sure to include "Hurricane Haven question" in the subject line.

Today's show will be about 20 minutes, and you can tune in at http://www.wunderground.com/wxradio/wubroadcast.h tml. The show will be recorded and stored as a podcast. I'll discuss 97L, and the odds of the U.S. getting a major hurricane strike during what remains of hurricane season.

Jeff Masters

Hurricane

Updated: 6:37 PM GMT on January 03, 2012

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97L still disorganized, but bringing heavy rains to the northeast Caribbean

By: JeffMasters, 12:27 PM GMT on October 04, 2010

A large region of disturbed weather (Invest 97L) covers the Lesser Antilles Islands and waters near Puerto Rico and the Virgin Islands. The storm is headed west-northwest at about 10 mph, and will bring heavy rain showers and gusty winds to the Lesser Antilles, Puerto Rico, the Virgin Islands, and the Dominican Republic today. These showers can be seen on Martinique radar this morning, and Martinique reported a wind gust of 35 mph this morning during one of 97L's heavy squalls. An upper level trough of low pressure is contributing to the heavy rain showers by making the atmosphere more unstable. This same trough is also bringing moderate wind shear of 10 - 20 knots, which will keep any development today very slow to occur. Recent satellite imagery shows a large area of intense thunderstorms associated with 97L, but the activity is not well organized, and there are no signs of a surface circulation. Long range radar out of Puerto Rico also shows no signs of rotation.


Figure 1. Morning satellite image of Invest 97L.

Forecast for 97L
The SHIPS model predicts that wind shear over 97L will slowly fall over the next three days, reaching the low range, 5 - 10 knots, by Thursday, which may allow the storm to develop into a tropical depression, if its center can stay over water. All of the major computer models now show development of 97L into a tropical depression Wednesday or Thursday, just north of Hispaniola. By Thursday, a passing trough of low pressure is expected to pull 97L to the northeast away from Hispaniola, and rains should end by Friday on the island if this forecast verifies. NHC is giving 97L a 20% chance of developing into a tropical depression by Wednesday. 97L will move at about 5 - 10 mph today through Wednesday, bringing the potential for an extended 3-day period of heavy rains for the islands in its path. These rains may result in life-threatening flash flooding and mudslides in Puerto Rico and the Dominican Republic today through Wednesday, and for Haiti Tuesday through Thursday. Flash flood watches are posted for the Virgin Islands and Puerto Rico today.

Elsewhere in the tropics
An area of disturbed weather near 10N, 47W is under a high 20 knots of wind shear, and is headed northwest into a region of even higher wind shear of 20 - 30 knots. Satellite imagery shows only a limited amount of heavy thunderstorms, and there is plenty of dry air in the vicinity that is interfering with development. NHC is giving the disturbance a 10% chance of developing into a tropical depression by Wednesday.

Most of the models indicate the possibility that a strong tropical disturbance capable of becoming a tropical depression will form in the Central or Southern Caribbean 6 - 8 days from now.

Next update
I'll have an update Tuesday morning.

Jeff Masters

Hurricane

Updated: 6:37 PM GMT on January 03, 2012

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97L a heavy rain threat to the Lesser Antilles and Puerto Rico today

By: JeffMasters, 2:51 PM GMT on October 03, 2010

A large region of disturbed weather (Invest 97L), centered about 200 miles east of the northern Lesser Antilles Islands, is headed west to west-northwest at about 10 mph and will bring heavy rain showers and gusty winds to the northern Lesser Antilles Islands, Puerto Rico, and the Virgin Islands today through Tuesday. These showers can be seen on Martinique radar this morning, and have increased considerably since yesterday, thanks to the presence of an upper level trough of low pressure making the atmosphere more unstable. This same trough is also bringing high wind shear of 20 -25 knots, though, so development of 97L is not expected today. Recent satellite imagery shows a large area of intense thunderstorms associated with 97L, but the activity is not well organized. The SHIPS model predicts that wind shear over 97L will fall to the moderate range, 10 - 20 knots, Monday through Thursday. The ECMWF model continues to be the only model showing significant development 97L in the next seven days. The model predicts 97L will be near Puerto Rico on Monday, the Dominican Republic on Tuesday, and Haiti on Wednesday, with the storm developing into a tropical depression on Thursday just north of Haiti, then moving northwards through the Turks and Caicos Islands and out to sea on Thursday. NHC is giving 97L a 10% chance of developing into a tropical depression by Tuesday, and has not tasked the Hurricane Hunters to fly into the storm over the next two days. 97L will move at about 10 mph through the islands today through Wednesday, bringing the potential for an extended 3-day period of heavy rains for the islands in its path. These rains may result in life-threatening flash flooding and mudslides in Puerto Rico and the Dominican Republic beginning on Monday, and for Haiti beginning on Tuesday. Flash flood watches are posted for the Virgin Islands and Puerto Rico today.


Figure 1. Morning satellite image of Invest 97L.

Flood waters receding in northeastern North Carolina
Flood waters are receding in northeastern North Carolina, where the Cashie River in Windsor caused major flooding that put many homes under five feet of water. North Carolina was deluged by more than twenty inches of rain in some regions over the past week, due to tropical moisture streaming northwards in advance of Tropical Storm Nicole. Representatives from Portlight.org are surveying the hardest-hit areas of North Carolina to begin identifying needs in the wake of the flooding. Portlight expects to perform the first deployment of their new relief trailer within the next few days and send a truck loaded with water, food and personal hygiene supplies. You can follow their progress via the Portlight.org blog.

Our new Weather Extreme blogger, Christopher C. Burt, has posted a comparison of the maximum rainfall totals in each state affected by Hurricane Floyd of 1999, and this weeks extreme rainfall event, which he dubs "Super-Rainstorm Nicole." The two storms were very similar in the amount of rain they dumped, and we are very fortunate that moderate drought conditions preceded the arrival of this week's storm, or else billions in damage would have resulted.


Figure 2. Rainfall for the 7-day period ending at 8am EDT this morning shows the remarkable accumulations that fell in association with the tropical moisture ahead of Tropical Storm Nicole. Image credit: NOAA.

Elsewhere in the tropics
An area of disturbed weather near 9N, 44W is fairly close to having a closed circulation, as seen on a 8:04am EDT pass by the ASCAT satellite. However, satellite imagery shows only a limited amount of heavy thunderstorms, and there is plenty of dry air in the vicinity that is interfering with development. The disturbance is headed to the northwest, and the computer models predict the disturbance will not affect any land areas for at least the next seven days. NHC is giving the disturbance a 10% chance of developing into a tropical depression by Tuesday.

Next update
I'll have an update Monday morning.

Jeff Masters

Hurricane

Updated: 11:38 PM GMT on October 03, 2010

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97L to spread heavy rains in Lesser Antilles; major flooding in North Carolina

By: JeffMasters, 3:42 PM GMT on October 02, 2010

A large region of disturbed weather (Invest 97L), centered about 400 miles east of the northern Lesser Antilles Islands, is headed west-northwest at about 15 mph and will bring heavy rain showers and gusty winds to the northern Lesser Antilles Islands today and Sunday. These showers can be seen approaching the islands on Martinique radar this morning. Wind shear is a moderate 10 - 20 knots over 97L, and the waters beneath are very warm, 29°C, but recent satellite imagery shows that 97L's heavy thunderstorms are limited and not well organized. A pass from the Windsat satellite at 5:51am EDT showed a moderate wind shift associated with 97L, but nothing close to a closed circulation. Top winds were around 30 - 35 mph. The SHIPS model predicts that wind shear over 97L will rise to the high range, 20 - 30 knots, today through Monday, then decline. The ECMWF model is the only model currently showing significant development 97L in the next seven days. The model predicts 97L will be near Puerto Rico on Monday, the Dominican Republic on Tuesday, and Haiti on Wednesday, with the storm developing into a tropical depression on Wednesday just north of Haiti, then moving northwards through the Turks and Caicos Islands and out to sea on Thursday. NHC is giving 97L a 20% chance of developing into a tropical depression by Monday, and has not tasked the Hurricane Hunters to fly into the storm over the next two days. 97L will move at about 10 mph through the islands on Sunday through Wednesday, bringing the potential for an extended 3-day period of heavy rains for the islands in its path. Even if 97L does not develop into a tropical depression, its slow motion may result in life-threatening flash flooding and mudslides in Puerto Rico, the Dominican Republic, Haiti, and eastern Cuba as it moves past.


Figure 1. Morning satellite image of Invest 97L.

Major flooding in northeastern North Carolina
Major flooding continues in northeastern North Carolina, where the Cashie River in Windsor is 5.4 feet over flood stage. North Carolina has been deluged by more than twenty inches of rain in some regions over the past week, due to tropical moisture streaming northwards in advance of Tropical Storm Nicole. Wilmington, NC set records this week for the heaviest 3-day, 4-day, and 5-day rainfall events in city history, and the month of September ended up as the second rainiest month ever recorded in the city. A remarkable 22.54" of rain fell on Wilmington during the 5-day period Sunday through Thursday. The previous record was 19.06", set in September 1999 during Hurricane Floyd. Fortunately, eastern North Carolina was under moderate drought conditions prior to this week's rainfall onslaught, with just 0.18" of rain falling during the first 25 days of September. Representatives from Portlight.org are on their way to the hardest-hit areas of North Carolina to beginning identifying needs in the wake of the flooding. Portlight expects to perform the first deployment of their new relief trailer within the next few days and send a truck loaded with water, food and personal hygiene supplies. You can follow their progress via the live webcam on the Portlight truck.

Our new Weather Extreme blogger, Christopher C. Burt, has posted a comparison of the maximum rainfall totals in each state affected by Hurricane Floyd of 1999, and this weeks extreme rainfall event, which he dubs "Super-Rainstorm Nicole." The two storms were very similar in the amount of rain they dumped, and we are very fortunate that moderate drought conditions preceded the arrival of this week's storm, or else billions in damage would have resulted.


Figure 2. Rainfall for the 7-day period ending at 8am EDT this morning shows the remarkable accumulations that fell in association with the tropical moisture ahead of Tropical Storm Nicole. Image credit: NOAA.

Elsewhere in the tropics
Disturbed weather has diminished in the Central Caribbean, where the remnants of Tropical Storm Nicole are no longer kicking up significant thunderstorm activity. Several of the models are predicting the formation of a tropical depression in the Mid-Atlantic 6 - 8 days from now, in a location that would not be of any danger to land areas.

Next update
I'll have an update Sunday morning.

Jeff Masters

Flood Hurricane

Updated: 3:54 PM GMT on October 02, 2010

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97L a major rainfall threat; October hurricane outlook; NC rains finally end

By: JeffMasters, 2:08 PM GMT on October 01, 2010

A large and complex region of disturbed weather (Invest 97L), centered about 800 miles east of the Lesser Antilles Islands, is headed west-northwest at 15 - 20 mph and will bring heavy rain showers and gusty winds to the northern Lesser Antilles Islands on Saturday and Sunday. Wind shear is a moderate 5 - 15 knots over 97L, and the waters beneath are very warm, 29°C. However, recent satellite imagery shows that the intensity and areal coverage of 97L's heavy thunderstorms have decreased this morning, thanks to some dry air being ingested into the storm. The SHIPS model predicts that wind shear over 97L will rise to the high range, 20 - 30 knots, Saturday through Tuesday, but some of the global computer models depict only moderate amounts of shear for 97L during this period. The NOGAPS model is the only model currently showing significant development 97L, and that model predicts 97L will be near Puerto Rico on Monday, the Dominican Republic on Tuesday, Haiti on Wednesday, and Eastern Cuba and the southeast Bahamas on Thursday. NHC is giving 97L a 40% chance of developing into a tropical depression by Sunday, but as of this morning, had not tasked the Hurricane Hunters to fly into the storm over the next two days. 97L will slow down to 5 - 10 mph on Sunday, bringing the potential for an extended 3 - 4 day period of heavy rains for the islands in its path. Even if 97L does not develop into a tropical depression, its slow motion may result in life-threatening flash flooding and mudslides in Puerto Rico, the Dominican Republic, Haiti, and eastern Cuba next week.


Figure 1. Morning satellite image of Invest 97L.

October hurricane outlook
October is here, and it is time to take stock of where we stand and how far we have to go before hurricane season is over. The beginning of October traditionally marks the two-thirds point of hurricane season; approximately one-third of all hurricanes and 28% of named storms occur after October 1. Tropical Storm Nicole brought us up to fourteen named storms for the year, and I expect about 4 - 5 more named storms this year with 2 - 3 of these being hurricanes. That would add up to 18 - 19 named storms for the season, putting 2010 in 3rd - 5th place all-time for most named storms. Since record keeping began in 1851, only four seasons have finished with more than eighteen named storms. These seasons were 2005 (28 named storms, with the 17th named storm, Rita, occurring by October 1); 1933 (21 named storms, with the 18th named storm occurring by October 1;) 1995 (19 named storms, with the 15th named storm, Opal, occurring by October 1;) and 1887 (19 named storms, with the 10th named storm occurring by October 1.) The most likely time to get activity is during the first two weeks of October. There are still two weeks of peak hurricane season left before the activity traditionally begins to decline steeply (Figure 2.) Given the record warm sea surface temperatures in the Atlantic this fall, the presence of La Niña in the Eastern Pacific keeping wind shear lower than average, and the observed increase in late-season activity in recent decades, I expect this year's peak portion of hurricane season will last until the end of October. I predict three named storms, two hurricanes, and one intense hurricane will form in the Atlantic this month, with two named storms and one hurricane occurring in November - December, making 2010 as the third busiest Atlantic hurricane season of all-time.


Figure 2. Climatological frequency of Atlantic named storms and hurricanes.

Jamaica cleans up after Nicole
Tropical Storm Nicole lasted only six hours as a tropical storm, but the storm's torrential rains hit Jamaica hard. Nicole's rains killed at least six people on the island, and at least thirteens others are missing and feared dead. The storm cut power to 170,000 island residents, and caused millions of dollars in damages. Wunderground member JamaicaZed wrote me to say his rain gauge in the Kingston suburb of Norbrook caught 17.39" of rain Monday through Thursday, with 11.10" coming on Wednesday.

Historic rainfall event for eastern North Carolina ends
The rains have finally ended In North Carolina, where tropical moisture streaming northward in advance of Nicole generated a historic rainfall event this week. Wilmington, NC set records this week for the heaviest 3-day, 4-day, and 5-day rainfall events in city history, and the month of September ended up as the second rainiest month ever recorded in the city. A remarkable 22.54" of rain fell on Wilmington during the 5-day period Sunday through Thursday. The previous record was 19.06", set in September 1999 during Hurricane Floyd. Fortunately, eastern North Carolina was under moderate drought conditions prior to this week's rainfall onslaught, with just 0.18" of rain falling during the first 25 days of September. Only minor to moderate flooding is occurring on North Carolina rivers, with just one river, the Northeast Cape Fear River near Chinquapin, expected to experience major flooding. Portlight.org is beginning to identify needs in Eastern North Carolina in the wake of the flooding, and expects to perform the first deployment of their new relief trailer within the next few days and send a truck loaded with water, food and personal hygiene supplies.

The most remarkable thing about Wilmington's second-wettest month in history is that it came without a hurricane affecting North Carolina. All four of the other top-five wettest Septembers in history were due, in large part, to hurricanes:

#1 23.41 inches 1999 (Hurricanes Dennis and Floyd)
#2 22.72 inches 2010 (plume of tropical moisture in advance of TS Nicole)
#3 20.10 inches 1877 (Hurricane Four)
#4 18.94 inches 1984 (Hurricane Diana)
#5 16.93 inches 1924 (Hurricane Five and Tropical Storm Eight)


Figure 3. Radar-estimated precipitation for North Carolina since Sunday shows that the precursor moisture from Nicole has brought widespread rain amounts of fifteen inches (white colors.)

Heavy rains and flooding for New England
The plume of tropical moisture that affected North Carolina is now triggering heavy rains in New England, and flood warnings are posted throughout most of New Jersey, eastern Pennsylvania, eastern New York, Delaware, and Vermont this morning. In New York City, heavy rains this morning have overwhelmed one section of the city's subway system, and flooding closed several key road arteries in the city, snarling the morning commute. About two inches of rain have fallen so far this morning in the city. Severe weather is not expected, and no tornadoes were reported yesterday in association with this weather system.

Elsewhere in the tropics
Disturbed weather continues in the Central Caribbean, where the remnants of Tropical Storm Nicole will bring isolated heavy rain showers today to Hispaniola, Jamaica, Cuba, the Cayman Islands, and northern Honduras. The GFS model predicts this activity will concentrate near Hispaniola over the weekend, then push northwards into the Bahamas, with a subtropical or extratropical storm forming over the Bahamas on Sunday or Monday. This storm could bring 2 - 4 inches of rain to the Bahamas Sunday and Monday. The storm will then move north-northeastwards, parallel to the U.S. East Coast, and not affect any other land areas. Several of the models are predicting the formation of a tropical depression in the Mid-Atlantic 5 - 7 days from now, in a location that would not be of any danger to land areas.

Next update
I'll have an update Saturday morning.

Jeff Masters

Flood Hurricane

Updated: 5:26 PM GMT on October 01, 2010

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About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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