Dr. Jeff Masters' WunderBlog

August hurricane outlook, Part I: SSTs

By: JeffMasters, 2:58 PM GMT on July 31, 2006

Before we get into the outlook for this August, let's discuss the current area of concern. A tropical wave near 16N 57W, about 300 miles east of the Lesser Antilles Islands, continues to be a threat as it moves west-northwest at 15-20 mph. Visible satellite imagery shows a very robust surface circulation, but little thunderstorm activity associated with the wave. Strong upper level winds from the northwest are creating about 20 knots of wind shear over the low, and this is keeping what little thunderstorm activity it has confined to the southeast quadrant. A 5:30 am EDT pass from the QuikSCAT satellite revealed surface winds of about 30 mph in this region. The low is embedded in a large area of dry, dust-laden Saharan air that moving west along with the low, limiting any chance the system has for intensification. In addition, wind shear is increasing in the region just ahead of the low's track, and should be high enough to prevent it from becoming a tropical depression today. The shear may relax down to the 15-20 knot range on Tuesday as the storm passes through the Lesser Antilles Islands near Guadaloupe, but dry air should still be a problem for it then. We still have one model that develops the system into a tropical storm--the GFDL model predicts that the system will hit Puerto Rico as a tropical depression on Wednesday, then intensify into a tropical storm that hits the Dominican Republic on Thursday. None of the other models buy this solution, and neither do I. Wind shear and dry air will probably combine to keep this wave from developing. Even if the wave does develop, a strong upper-level cold low north of the Bahamas will bring very hostile wind shear to any storm that tries to approach the U.S. East Coast through the Bahamas. The only chance the storm appears to have is if it can stay south of the Dominican Republic in the Caribbean Sea.

The Hurricane Hunters are on call this afternoon and tomorrow in case a reconnaissance flight is needed into the system. Let's hope they get to enjoy the beach instead!


Figure 1. Preliminary model tracks for the tropical wave approaching the Lesser Antilles Islands.

New development off the Carolina coast
A non-tropical low pressure center has developed about 150 miles east-southeast of Cape Hatteras North Carolina. Wind shear is a very high 30-40 knots today over the disturbance, but may slowly decrease over the next few days, possibly allowing some slow development. The low is currently moving slowly east-southeastward, but is in an area of weak steering currents.


Figure 1b. Preliminary model tracks for the low off the Carolina coast.

August Sea Surface Temperature Outlook
Sea Surface Temperatures (SSTs) throughout the tropical Atlantic are very near normal for this time of year (Figure 2). Contrast this with last year, when we had the highest SSTs ever recorded in the tropical Atlantic--about 2 degrees C higher than normal. This difference in SSTs is primarily due to the stronger than normal trade winds we've had during June and July this year. A much stronger Bermuda High than last year's has been driving increased trade winds and higher evaporative cooling of the ocean.


Figure 2. Departure of SST from normal for July 28, 2006. Image credit: NOAA.

What are SSTs likely to do in August?
As we can see from the long range forecast from NOAA, SSTs are expected to remain near normal for the duration of hurricane season. The Bermuda High and the trade winds it drives are expected to be near normal, resulting in normal SSTs. Now, these long range forecasts are not that reliable, but do have some skill compared to flipping a coin. I believe that for at least the month of August, the forecast is correct, since the 2-week GFS forecast is indicating near-normal winds and pressures across the Atlantic.


Figure 3. Forecast departure of SST from normal for August through October , 2006. Image credit: NOAA's Climate Prediction Center.

Total heat content of the ocean
As most of you are aware, hurricanes generally require sea surface temperatures (SSTs) of at least 80 F (26.5 C) to exist, and the hotter the water, the better.Hurricanes also like to have these warm ocean waters extend to a depth of several hundred feet, since the winds of a hurricane generate ocean turbulence that stirs up colder water from the depths to the surface. Hurricane that pass over a region of ocean with very deep warm waters can intensify explosively; this happened with Katrina, Rita, and Wilma in 2005. A good way to monitor this total oceanic heat is with the Tropical Cyclone Heat Potential (TCHP) imagery prepared daily by NOAA using satellite measurements of the height of the ocean surface. Hotter water expands, creating a higher water surface that the satellite can measure.

Let's take a look at the TCHP data from July 28 this year, and compare it to last year (Figures 4 and 5). The units of measurement are in kilojoules per square centimeter, and any value greater than 20 kJ/cm**2 (a medium blue color) is high enough to support a Category 1 hurricane. A TCHP greater than 90 kJ/cm**2 (orange color) can lead to rapid intensification of a hurricane. The TCHP image from last year shows a large area of oranges and reds in excess of the 90 kJ/cm**2 threshold for rapid hurricane intensification covering most of the Gulf of Mexico, Caribbean, and tropical Atlantic. A red bullseye in the Gulf of Mexico marks the Loop Current Eddy that broke off in the Gulf last July, and helped fuel Katrina and Rita to record intensities.

In contrast, the TCHP image for this year shows the oranges and reds covering just a portion of the western Caribbean and southern Gulf. There is much less heat energy available to fuel intense hurricanes, and thus we should see fewer of them this year than in 2005 (or 2004, which also had very high TCHP values). However, we again see an ominous looking red bullseye in the central Gulf of Mexico this year, similar to what was there last year.


Figure 4. Tropical Cyclone Heat Potential (TCHP) for July 28, 2005.


Figure 5. Tropical Cyclone Heat Potential (TCHP) for July 28, 2006.

Another dangerous Loop Current Eddy in 2006
As I described in my May 2006 Gulf of Mexico Loop Current outlook, the Loop Current is an ocean current that transports warm Caribbean water through the Yucatan Channel between Cuba and Mexico. The current flows northward into the Gulf of Mexico, then loops southeastward through the Florida Keys (where it is called the Florida Current), and into the Bahamas. Here, the waters of the Loop Current flow northward along the U.S. coast and become the Gulf Stream. During summer and fall, the Loop Current provides a deep (80 - 150 meter) layer of vary warm water that can provide a huge energy source for any lucky hurricanes that might cross over. Every 6 to 11 months, the Loop Current sheds an eddy that moves westward at 3-5 km per day across the Gulf of Mexico. These eddies can double the area of the Gulf where explosive hurricane intensification can occur. When the loop current sheds an eddy at the height of hurricane season, it's bad news for the residents along the Gulf Coast. This occurred in 2005, when a Loop Current Eddy separated in July, just before Hurricane Katrina passed over and "bombed" into a Category 5 hurricane.


Figure 6. Currents in the Gulf of Mexico on July 28, 2006. Red colors indicate fastest current speeds. Note the two eddies in the Gulf of Mexico that have separated from the Loop Current. Image credit: Navy Research Lab.

Unfortunately, there's bad news again this year. Another Loop Current Eddy has just separated, and is now spinning in the central Gulf of Mexico, ready to fuel explosive intensification of any system that might cross the Gulf. The position of this year's eddy makes it primarily a threat for hurricanes that would hit Mississippi, Louisiana, or the upper Texas coast. The behavior of the Loop Current over the past year can be viewed at Navy Research Lab's web site (51 Mb). This movie has arrows showing the direction of the current, plus a color coding that represents the height of the sea surface above mean level. The higher the height, the warmer the water (since warm water expands and thus raises the sea level where it is at). One can see near the beginning of the animation that the Loop Current Eddy that fueled Katrina and Rita that broke off in July 2005. Another eddy breaks off in March 2006, and the final eddy during the past two weeks. The old March eddy has only a little extra heat content, but the new eddy is similar in heat content and only about 25% smaller in size than the eddy that fueled the intensification of Katrina and Rita in 2005. Let's hope we don't get a hurricane in the Gulf this year that crosses over this eddy! I'll talk about the possibilities of that happening in Part II of this blog on Tuesday.

Jeff Masters


Updated: 3:29 PM GMT on July 31, 2006

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Watching the same two tropical waves

By: JeffMasters, 1:40 PM GMT on July 30, 2006

A tropical wave about 600 miles east of the Lesser Antilles Islands continues to be a threat as it moves west-northwest at 15-20 mph. A good pass by the QuikSCAT satellite this morning at 5:38 EDT revealed that a center of low pressure was located near 10N 51W, but the wave did not have a closed surface circulation. The main thunderstorm activity was to the north of the low's center, with winds in the 30-35 mph range at the surface. Visible satellite imagery from this morning confirm that the wave has no surface circulation, and shows a few heavy thunderstorms to the north of the center. The wave is surrounded by a large area of dry, dust-laden air to its north and west. This dry air, plus wind shear of 10-20 knots, should make any development slow to occur. However, for the first time, we do have a model that develops the wave. Last night's run of the GFDL model has the wave developing into a tropical storm by Monday night, when it crosses through the Leeward Islands near Guadeloupe. The GFDL then brings the tropical storm across the Dominican Republic on Wednesday night. None of the other models buy this solution, and predict that wind shear and dry air will keep this wave from developing. That is my expectation as well. Even if the wave does develop, a strong upper-level cold low north of the Bahamas will bring very hostile wind shear to any storm that tries to approach the U.S. East Coast. The GFDL model reflects this, and has the storm weakening as it crosses into the Bahama Islands late in the week.


Figure 1. Preliminary model tracks for the tropical wave approaching the Lesser Antilles Islands.

Tropical wave near Puerto Rico
An area of heavy thunderstorms associated with a tropical wave lies near Puerto Rico, and has brought up to three inches of rain to eastern Puerto Rico in the past day. Long range radar out of Puerto Rico reveals no organization to the radar echoes. There is no dry Saharan air nearby, and wind shear over this disturbance is marginal for development, 15-20 knots, so some slow development is possible over the next day or two. However, the wave is headed west-northwest at about 10-15 mph into a area of higher wind shear associated with the upper-level low pressure system spinning north of the Bahama Islands. I don't expect the wave will develop, although it may bring heavy rains to Florida by Wednesday.

Monday I'll post part one of a two part series analyzing the August hurricane outlook.

Jeff Masters

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Two waves to watch

By: JeffMasters, 2:06 PM GMT on July 29, 2006

The tropical wave near 9N, 46W, about 1000 miles east of the southernmost Lesser Antilles Islands, continues to show signs that it may organize into a tropical depression. While we don't have a good recent QuikSCAT pass to look at, this morning's visible satellite imagery shows a pronounced surface circulation. However, the amount of heavy thunderstorm activity has greatly decreased since yesterday, due to the ingestion of dry Saharan air from the north (Figure 1). Dry air will continue to be a problem for the wave the farther north it goes. The forecast tracks from the latest computer models (Figure 2) show a mostly westward track, but the wave is expected to slowly gain latitude, putting it more into the influence of this very dry air from Africa.


Figure 1. Saharan air layer (SAL) analysis from 8am EDT Sat Jul 29. Dry, dust laden air from the Sahara desert is coded orange, and lies just north of the tropical wave we're tracking. Image credit: University of Wisconsin CIMSS and NOAA's Hurricane Research Division.

In the wave's favor, it is under only 5-10 knots of wind shear, and this shear is forecast to remain weak over the next two days. As the wave approaches the Lesser Antilles Islands on Monday, shear is forecast to increase again. Sea surface temperatures are favorable--28 C, about 2 degrees C above the threshold of 26 C needed for tropical storm formation.

The long term outlook for the system is not favorable, due to the large amount of dry air to its north and the increasing wind shear likely to affect the system once it nears the islands. In addition, the wave is expected to cross into the southeast Caribbean. This region is climatologically unfavorable for tropical cyclones, because the land mass of South America cuts off the inflow of moist air from the south, replacing it with drier continental air.

None of the computer models develop this wave into a tropical storm.


Figure 2. Preliminary model tracks for the tropical wave approaching the Lesser Antilles Islands.

Tropical wave south of Puerto Rico
An area of heavy thunderstorms associated with a westward-moving tropical wave has increased in coverage just south of Puerto Rico and the Dominican Republic this morning. Wind shear over this disturbance is marginal for development, 10-20 knots, so some slow development is possible over the next few days. This disturbance probably has more potential than the other wave, due to the presence of much moister air in the Caribbean.

Jeff Masters

Updated: 3:25 PM GMT on July 29, 2006

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New tropical wave has potential to develop

By: JeffMasters, 2:17 PM GMT on July 28, 2006

A new area of concern has developed near 8N 38W, about 1500 miles east of the southernmost Lesser Antilles Islands. Residents of the islands will want to keep a close watch on this tropical wave over the next few days, as it has the potential to develop into a tropical storm. The tropical wave has a concentrated area of heavy thunderstorms, some upper level outflow, and the beginnings of a surface circulation. The latest pass of the QuikSCAT satellite at 4:44am EDT today showed a strong wind shift associated with the wave, but not a closed circulation at the surface. Winds in the strongest thunderstorms were about 30-35 mph, with one heavy squall ahead of the wave creating winds of up to 50 knots (57 mph).


Figure 1. QuikSCAT winds from 4:44am EDT Fri Jul 28. The winds are plotted using the standard station model. The black wind barbs mark where it is raining. Only the colored wind barbs are reliable. Black ones are unreliable, as rain contaminates the measurement of wind by the QuikSCAT satellite.

The wave is under about 15 knots of wind shear, and this shear is forecast to gradually weaken over the next two days, which may allow the wave to organize into a tropical depression. This organization will be slowed by the wave's close proximity to the Equator. Disturbances south of about 10 degrees north latitude frequently have trouble organizing, since they can't leverage the Earth's spin much to help them develop their own circulation. The forecast track of the system (Figure 2) takes it west at about 20 mph through Sunday, then curves it more to the west-northwest. Some very dry air laden with African dust lies to the north, so this may act to inhibit development. Once the wave nears the islands, some significant wind shear may affect it, but it is too early to be confident of this forecast.


Figure 2. Preliminary model tracks for the tropical wave approaching the Lesser Antilles Islands.

Tropical wave over the Bahamas and central Caribbean
A tropical wave over the southeastern Bahama Islands extends south through the central Caribbean to Columbia. This wave is moving west-northwest at 20-25 mph, and is not expected to develop today or Saturday due to wind shear of 20 knots. The wave should reach the Gulf of Mexico on Sunday, where wind shear will be marginal for development.

Jeff Masters

Updated: 2:21 PM GMT on July 28, 2006

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Quiet tropics today

By: JeffMasters, 1:15 PM GMT on July 27, 2006

The tropical Atlantic is quiet today, with just two tropical waves to talk about. Neither of these waves looks like a threat to develop into a tropical storm. The wave near Puerto Rico is moving west at 20-25 mph, and is under about 30 knots of winds shear. This shear is forecast to remain above 20 knots through Saturday, when the wave should be affecting Florida and the Western Caribbean.

A second wave near 10N 45W, about 600 miles east of the South American coast, is under less wind shear, about 10-20 knots. There is a circulation at low and mid levels evident in satellite imagery. Dry Saharan air nearby should inhibit development of this wave, and it is also too close to the Equator to show any development today.


Figure 1. Visible satellite image of today's tropical Atlantic, showing the two tropical waves.

The long range GFS forecast is no longer calling for a Cape Verdes hurricane to form August 3 and threaten the Lesser Antilles Islands later that week. However, the model is showing an increase in activity in the tropics between Africa and the Islands starting the second week of August, which is normal for that time of year.

Jeff Masters

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Quiet tropics--for now

By: JeffMasters, 1:51 PM GMT on July 26, 2006

The disturbance in the Gulf of Mexico has moved far enough on shore that it no longer has a chance to become a tropical depression. This system will bring heavy (and welcome!) rains to portions of Texas and Louisiana over the next two days.

Tropical Depression Daniel has decayed into a swirl of low clouds, and is expected to dissipate before reaching the Hawaiian Islands. All the Hurricane Hunter flights scheduled to investigate the storm have been canceled.

A tropical wave a few hundred miles east of the northernmost Lesser Antilles Islands is moving west to west-northwest at 15-20 mph. The amount of thunderstorm activity associated with this wave has increased over the past day, as the dry Saharan air surrounding the wave has gradually diluted. However, the wave is now under 30 knots of vertical wind shear. This wind shear is being created by the counter-clockwise flow of air around an upper-level low pressure system to the north of Puerto Rico. This low is not expected to move much the next five days, and should continue to create hostile wind shear over the wave. The wave will spread showers and gusty winds to Puerto Rico on Thursday, and the Bahama Islands on Friday and Saturday. By Saturday, as the wave approaches Florida, it will not be as close to the upper-level low, and the shear may lessen, potentially allowing some development. The wave is expected to turn north towards the Carolinas and not enter the Gulf of Mexico.


Figure 1. Water vapor image from 8:15 am EDT today shows a tropical wave surrounded by dry Saharan air approaching the Lesser Antilles Islands. The brown colors show the driest air, and whites and blues show where the most moisture is. You can see a large swirl of moisture north of Puerto Rico that marks the counter-clockwise rotating upper-level low pressure system that is bringing hostile wind shear over the tropical wave.

Long range forecast
The past four runs of the GFS model have consistently shown a powerful Cape Verdes-type hurricane forming off the coast of Africa August 3, tracking westward, and hitting the northernmost Lesser Antilles Islands on August 7. While I will be amazed if this forecast verifies--since our computer models are not very talented at forecasting tropical storm formation one day in advance, let alone a week or ten days in advance--it does serve as a reminder that we are entering August next week, and we should not be surprised if these most dangerous of hurricanes start forming from tropical waves coming off the coast of Africa.

Jeff Masters

Updated: 1:58 PM GMT on July 26, 2006

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Gulf distubance, Hawaii and Daniel

By: JeffMasters, 2:14 PM GMT on July 25, 2006

An area of low pressure centered near the Mexican coast about 45 miles southwest of the Texas/Mexico border continues to generate intense thunderstorms with strong wind gusts over the western Gulf of Mexico. However, the disturbance has not become any better organized since yesterday, and the winds at the surface have decreased. Winds this morning at buoy 42002, 275 miles south-southeast of Sabine, TX, have only gusted up to 29 mph, compared to the 51 mph gusts measured yesterday. The disturbance shows no signs of a circulation, as one can monitor via Brownsville, TX radar. Wind shear over the disturbance has increased 5 knots since yesterday, and should remain high enough today to prevent development of a tropical depression. By Thursday, wind shear may decline enough to allow a tropical depression to form, if the center is over water. The center is moving slowly northwards. but could re-emerge over water Wednesday or Thursday.


Figure 1. Preliminary model forecast tracks for the area of disturbed weather in the Southwest Gulf of Mexico.

Wave approaching the Lesser Antilles
A large tropical wave with a surface circulation near 14N 51W, 650 miles east of the Lesser Antilles Islands, is moving west at 15 mph. It should reach the Lesser Antilles islands on Thursday, and Bahamas on Saturday. The wave is surrounded by a huge cloud of African dust and dry air, and thunderstorm activity is currently minimal. No development is expected while the wave remains in this dry environment. We'll have to keep an eye on this wave later in the week, when it may encounter a moister environment.

Daniel eyes Hawaii
Tropical Storm Daniel is headed towards Hawaii, with a Friday landfall expected. However, Daniel is a skeleton of its former Category 4 glory, and may only be a tropical depression at landfall. This morning's satellite imagery shows that the cool 24-25 C waters beneath Daniel have robbed the storm of almost all of its intense thunderstorm activity. Daniel appears as just a swirl of low clouds, and will continue to weaken over the next few days as it remains over cool waters. Waters very near Hawaii do warm up to 26 C, so Daniel may be able to make a minor comeback shortly before landfall. The Hurricane Hunters are scheduled to start flying into the storm Wednesday afternoon, if Daniel still poses a threat.


Figure 2. Current satellite image of Daniel.

It's hot in Death Valley
The low temperature in Death Valley yesterday morning was 100, perfect for the start of the Badwater Ultramarathon. The 135-mile, three-day race across Death Valley to Mt. Whitney is in full swing today. With high temperatures of 123 expected today, I'm sure the competitors will be satisfied that the race will be sufficiently challenging.

Jeff Masters

Updated: 3:27 PM GMT on July 25, 2006

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Gulf of Mexico disturbance; Ultramarathon today in Death Valley

By: JeffMasters, 2:01 PM GMT on July 24, 2006

An area of disturbed weather associated with a tropical wave and a weak trough of surface pressure is generating some intense thunderstorms with strong wind gusts over the southwestern Gulf of Mexico. At 10am EDT, the winds at buoy 42002, 275 miles South-Southeast of Sabine, TX, recorded a wind gust of 50 mph. Sustained winds have been in the 25-30 mph range at this buoy the past few hours. The thunderstorm activity has increased since yesterday, but wind shear remains high, 15-25 knots, which is probably too high to allow a tropical depression to develop today. There was a hurricane hunter flight scheduled to take off at 11:30am today to investigate the disturbance, but it was cancelled. The disturbance shows no signs of a ciculation, as one can monitor via Brownsville, TX radar.

Both the GFS and NOGAPS models are forecasting the wind shear to fluctuate up and down through Wednesday, but probably remain above 15 knots. This amount of shear is likely too much for the disturbance to develop into a tropical depression. By Thursday, the wind shear is forecast to drop sharply, increasing the chances for development--if the disturbance hasn't moved over land by then. The disturbance is close to the Mexican coast, and may move ashore by Tuesday near the Texas/Mexico border. NHC has not scheduled a Hurricane Hunter flight for Tuesday.


Figure 1. Preliminary model forecast tracks for the area of disturbed weather in the Southwest Gulf of Mexico.

New wave to watch
A large tropical wave with a surface circulation is near 14N 45W, 1100 miles east of the Lesser Antilles Islands. The wave is moving west at 15 mph, and should reach the Lesser Antilles islands on Thursday. The wave has entered a region of low wind shear of 5-10 knots which is forecast to persist for the next three days, so some slow development is possible. The primary impediment will be dry air--the wave is surrounded by a huge cloud of African dust and dry air, and thunderstorm activity is currently minimal. A Hurricane Hunter airplane is tenatively scheduled to investigate the system on Thursday.


Figure 2. This morning's visible image of a tropical wave to watch 1100 miles east of the Lesser Antilles Islands.

More heat news
The heat continued to set records across the Southwest U.S. over the weekend. On Saturday, the mercury hit an unofficial 120 degrees in Usta, South Dakota, tying that state's all-time high temperature record. The record is expected to be certified by the National Climatic Data Center, according to the local National Weather Service office. The 95 degree low temperature yesterday at Phoenix Sky Harbor International Airport tied the second all-time warmest low temperature. The all-time warmest low temperature was 96 degrees, set on July 15, 2003.

OK, this is NUTS!
The high temperature in Death Valley reached 125 degrees both Saturday and Sunday, which should cheer up the competitors in today's Badwater Ultramarathon, billed as "the most demanding and extreme running race offered anywhere on the planet". The race starts out in Badwater, Death Valley (just down the road from Furnace Creek, Dante's Peak, and other hellishly named Death Valley attractions!). The competitors run non-stop for 135 miles and three days across Death Valley in the heat of day, across three mountain ranges with a combined vertical ascent of 13,000', and finish at 8,000 feet altitude on Mt. Whitney. Not recommended for the sane!

Jeff Masters

Heat

Updated: 11:13 PM GMT on August 16, 2011

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More heat; Gulf of Mexico disturbance

By: JeffMasters, 4:32 PM GMT on July 23, 2006

The heat was unrelenting yesterday across the Southwest U.S., where most of California and Arizona set new high temperature records. The 99 degrees in downtown Los Angeles beat the old record of 96 set in 1960, and the suburb of Woodland Hills hit a record 119. All the cities in California's Central Valley set records: 109 degrees in Sacramento, 111 in Redding, and 112 in Red Bluff, Stockton and Modesto. San Francisco's 87 degrees easily beat the record of 81 for the date, set back in 1917.

In Phoenix, this morning's low temperature was 97 degrees, which broke the all-time record for highest low temperature ever recorded in that city (96, set on Jul 15, 2003). Tucson's low of 89 Saturday morning was its highest low temperature in recorded history, as well. The temperature topped out at record 116 in Phoenix yesterday, and 121 in nearby Gila Bend.

Tropical update
An area of disturbed weather continues over the southwestern Gulf of Mexico. Wind shear is over 20 knots in this region, which is too high to allow development today. Both the GFS and NOGAPS models are forecasting this shear to be 15 knots or higher over the next few days, and usually one needs wind shear to fall to the 10-15 knot range for development. However, the NHC is playing it cautiously and has put a Hunter airplane on call for Monday, if needed. I'll be surprised if this flight happens.


Figure 1. Preliminary model forecast tracks for the area of disturbed weather in the Southwest Gulf of Mexico.

Enjoy another quiet weekend in the tropics, everyone!
Jeff Masters

Heat

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The heat goes on...

By: JeffMasters, 3:13 PM GMT on July 23, 2006

The heat was unrelenting yesterday across the Southwest U.S., where most of California and Arizona set new high temperature records. The 99 degrees in downtown Los Angeles beat the old record of 96 set in 1960, and the suburb of Woodland Hills hit a record 119. All the cities in California's Central Valley set records: 109 degrees in Sacramento, 111 in Redding, and 112 in Red Bluff, Stockton and Modesto. San Francisco's 87 degrees easily beat the record of 81 for the date, set back in 1917.

In Phoenix, this morning's low temperature was 97 degrees, which broke the all-time record for highest low temperature ever recorded in that city (96, set on Jul 15, 2003). Tucson's low of 89 Saturday morning was its highest low temperature in recorded history, as well. The temperature topped out at record 116 in Phoenix yesterday, and 121 in nearby Gila Bend.

Tropical update
There is not much to talk about in the tropical Atlantic today. There is some disturbed weather in the southwestern Gulf of Mexico, but wind shear is over 20 knots in this region, and unlikely to fall to the 10-15 knot range needed for something to develop. Large amounts of African dust cover the tropical Atlantic and Caribbean Sea, discouraging development in those regions.

Enjoy another quiet weekend in the tropics, everyone!
Jeff Masters

Heat

Updated: 3:16 PM GMT on July 23, 2006

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The heat is on

By: JeffMasters, 2:16 PM GMT on July 22, 2006

Record heat has gripped much of the U.S. this week. The heat is currently most intense in the Desert Southwest, where yesterday Phoenix recorded its fourth highest temperature of all time, 118 F. Needles, California hit a record 120 yesterday, and the temperature topped out at 123 F in Death Valley--only 13 degrees cooler than the world record 136 F measured in El Azizia, Libya, in 1922. The heat should continue for another week in the Southwest, before a shift in the jet stream pattern brings more normal temperatures to the region late next week.

The heat is on in Europe, too
Europe has seen its own record heat wave this week. Britain broke its all-time July temperature record, with a 98 F (36.5 C) temperature recorded at the Royal Horticultural Society's gardens at Wisley in Surrey. This bested the previous record for July, 36 C, set in Epsom in 1911. Belgium also recorded its hottest July day ever, 99 F (37 C) on July 19. Paris and Berlin both recorded 102 F (39 C) on July 20. However, the 2006 heat wave has caused far fewer deaths than the intense heat wave of 2003 that killed over 35,000 people. The 2006 heat wave has claimed 20 victims in France, 2 in Spain, and 4 in Germany and the Netherlands. Much of the reduced death toll can be credited to better preparation learned from the 2003 heat wave.

The heat, combined with drought, has reduced the amount of cooling water available to cool the nuclear reactors in Germany and France, forcing those plants to cut back on electricity production. In Italy, hydroelectric power generation has been reduced due to the drought.

Warmest January through June ever in U.S.
The National Climatic Data Center reports that the June 2006 was the 2nd warmest June on record, and the first half of 2006 was the warmest in the United States since record keeping began in 1895. The average temperature for the 48 contiguous United States from January through June was 51.8�F, or 3.4�F above average for the 20th century. Globally, June was also the 2nd warmest June on record, and the period January through June was the 6th warmest such period on record.

Watching the tropics
There are no areas of disturbed weather to talk about the tropical Atlantic today, and none of the computer models are forecasting any development for the coming week.

The main action this week will be in the Eastern Pacific, where we have my favorite type of hurricane--a huge, spectacular Category 4 (almost 5) storm that is no threat to land. Daniel joins May's Typhoon Chanchu as the only Category 4/5 tropical cyclones in the Northern Hemisphere so far this year. Daniel could threaten Hawaii late next week, but the storm will probably be a weak tropical storm by that point, due to passage over cooler waters.


Latest satellite image of Hurricane Daniel

Jeff Masters

Heat

Updated: 11:14 PM GMT on August 16, 2011

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Beryl hits Nantucket

By: JeffMasters, 1:14 PM GMT on July 21, 2006

Tropical Storm Beryl moved rapidly over Nantucket Island, Massachusetts this morning, bringing gusty winds and heavy rain, but little damage. Seas reached 19 feet offshore Nantucket this morning, and large pounding waves of six to ten feet will cause minor beach erosion problems for the remainder of the day. The peak wind this morning measured at Nantucket Airport was 33 mph, gusting to 44 mph. The pressure bottomed out at 1001 mb at 3am. The Nantucket Shoals buoy reported peak 10-minute average winds of 41 mph with a gust to 56 mph. The heaviest rain stayed offshore, and only about an inch of rain fell on Nantucket. Beryl was a typical July tropical storm--a weak system good for testing our preparedness for when the real action starts in August.


Figure 1. Total rainfall from Beryl estimated from the Boston radar.

Beryl missed mainland Massachusetts, and is now on its way to a landfall in Nova Scotia. The storm is well on its way toward becoming a regular extratropical storm, and should have only a minor impact on Canada. Beryl is the first July tropical storm to hit New England since Tropical Storm Bertha of 1996.

Elsewhere in the tropics
There are no other disturbed areas of weather in the tropical Atlantic worthy of mention today. There are indications that the region between Africa and the Lesser Antilles Islands may become more favorable for tropical storm formation next week, though. There is less Saharan dust pushing off the coast of Africa, and both the GFS and Canadian models are suggesting a tropical storm could form by the middle of next week off the coast of Africa. However, there will still be a lot of wind shear present, and the chances of a significant storm developing and holding together are questionable. The basic weather pattern we've seen all of June and July shows no sign of changing, and significant hurricane activity appears likely to hold off until the usual time we're used to--early August.

I'll be back with an update Saturday.
Jeff Masters

Updated: 1:19 PM GMT on July 21, 2006

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Beryl weakening

By: JeffMasters, 7:24 PM GMT on July 20, 2006

Beryl has begun a slow decline in strength this afternoon. The latest Hurricane Hunter center report at 2pm EDT found the pressure unchanged from the 7am advisory, 1002 mb. Long range radar from Long Island (Figure 1) shows some good spiral banding, but the storm has a much more ragged appearance on satellite pictures. Infrared satellite imagery shows a substantial warming of the cloud tops, which means Beryl's thunderstorms are not reaching as high into the atmosphere. This morning's Central Dense Overcast (CDO) is gone. With the wind shear now rising steadily and sea surface temperatures declining, Beryl's winds will probably start to decrease late tonight. The Hurricane Hunters found top winds of only 45 mph at the surface in their 2pm pass through the storm, but hadn't sampled the entire storm yet.


Figure 1.Current long-range radar out of Long Island.

Impact on New England
A strong band of westerly upper-level winds over New England has turned Beryl to the north-northeast, and she will likely pass very close to Massachusetts' Nantucket Island early Friday morning. At 2pm EDT, waves at the Long Island buoy 38 miles south of Islip were up to 11 feet, and winds were gusting to 36 mph. Large waves on top of the expected 1-3 foot storm surge should cause some moderate beach erosion along the southeast Massachussetts coast. Fortunately, Beryl's closest approach to land at 4am EDT Friday coincides with low tide. Beryl will be moving quickly when it passes Massachusetts, and some of the heaviest rain will remain offshore, so flooding from rainfall should be minor. Rains of 1-4 inches are expected in southeast Massachussetts, Long Island, and Rhode Island.

Elsewhere in the tropics
An area of disturbed weather a few hundred miles north of Puerto Rico has diminished. A large cloud of African dust over the eastern Atlantic should keep things quiet there the rest of the week. None of the computer models are hinting at any development over the next week.

Jeff Masters

Updated: 7:29 PM GMT on July 20, 2006

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Beryl levels off in intensity

By: JeffMasters, 12:27 PM GMT on July 20, 2006

Beryl appears to have stopped intensifying. The latest Hurricane Hunter center report at 7:13 am EDT found that the pressure had risen 1 mb from the 5am advisory, to 1002 mb. Surface winds remained at about 60 mph. Long range radar from New Jersey (Figure 1) shows the storm's structure nicely. While there is some good spiral banding, the storm has been unable to close off an eye. Visible satellite imagery from this morning shows a Central Dense Overcast (CDO) typical of a hurricane trying to form over the southern portion of the storm, where the shear is less. With the wind shear now rising steadily and sea surface temperatures declining, it is unlikely that Beryl will be to make the transition to hurricane status, although a few more hours probably remain for this to happen. A slow decline in strength should begin tonight. Wind shear is currently 10 - 20 knots from the west, and should increase to 20 - 30 knots by Friday morning. Sea surface temperatures are 25 - 26 C, and will fall to 24 - 25 C.


Figure 1.Current long-range radar out of Philadelphia.

Impact on New England
A strong band of westerly upper-level winds over New England will act to turn Beryl more to the northeast today. It is possible that the storm could penetrate far enough north to strike southeast Massachussestts early Friday, as indicated by the GFS and GFDL models. However, the further north Beryl does go, the likelier she is to significantly weaken, since wind shear increases sharply to the north. A close pass by a 50-60 mph tropical storm or a strike by a weaker 40-50 mph tropical storm are the two most likely scenarios for southeast Massachussetts. In either case, beach erosion will probably be the primary threat. Already, the waves at the mid-ocean buoy 230 miles east of New Jersey are up to 12 feet, and large waves on top of the expected 1-3 foot storm surge should cause some moderate beach erosion along the southeast Massachussetts coast. Beryl will be moving quickly when it passes Massachussetts, and much of the heaviest rain will remain offshore, so flooding from rainfall should be minor. Rains of 2-4 inches are expected in southeast Massachussetts.

Elsewhere in the tropics
An area of disturbed weather associated with an upper-level low pressure system continues a few hundred miles north of Puerto Rico. Wind shear, dry air, and cold air temperatures will keep any development of this system to a minimum. A large cloud of African dust over the eastern Atlantic should keep things quiet there the rest of the week. None of the computer models are hinting at any development over the next week.

I'll be back with an update this afternoon. The next Hurricane Hunter flight is scheduled to arrive at 2pm EDT. And in case you were wondering how to pronounce Beryl, check out wunderblogger MargieKieper's humorous blog.

Jeff Masters

Updated: 3:43 PM GMT on July 20, 2006

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Beryl slowly intensifying

By: JeffMasters, 7:49 PM GMT on July 19, 2006

Tropical Storm Beryl continues to slowly intensify. This afternoon's Hurricane Hunter aircraft reported a central pressure of 1002 mb at 4:22pm EDT, down 2 mb from the 11am advisory. The plane found winds as high as 57 knots at flight level (5,000 feet), which corresponds to about 50 mph at the surface--a 5 mph increase from the 11am advisory. The plane also made a visual observation of 60 mph winds at the surface. Satellite imagery continues to show a large blow-up of thunderstorms with very cold tops on the northwest side of Beryl. These cold tops mean the thunderstorms are reaching high levels of the atmosphere, and are therefore very intense.

If we examine the sea surface temperature plot for this morning (Figure 1), we see that Beryl is crossing the axis of the warmest waters of the Gulf Stream. These warm 27 - 28 C waters are probably responsible for the current burst of intensification. Beryl is moving north and should stay over these warmer waters until about midnight, so we can expect continued intensification for a few more hours. By early Thursday, Beryl is expected to encounter a region of high wind shear, and SSTs will start to cool. This should start to weaken the storm. The two most reliable intensity models used by NHC both forecast that Beryl will be a weak tropical storm with top winds of 40 - 50 mph at closest approach to New England.

Figure 1. 3D image of sea surface temperatures for July 19, 2006. Beryl is headed due north across the warmest waters of the Gulf Stream current today. Image credit: NOAA Environmental Modeling Center.

Beryl is expected to continue moving north today, then turn more to the northeast on Thursday as a trough of low pressure approaches from the west. Just how strong this trough is will determine how close Beryl passes to New England. Some of the forecast models are forecasting a strike on Long Island or Cape Cod Friday, but the official NHC forecast of a turn out to sea just south of New England sounds more reasonable, given that no July tropical storm --and only one July hurricane (1916)--has ever made landfall in New England.

Elsewhere in the tropics
An area of disturbed weather associated with an upper-level low pressure system has developed a few hundred miles north of Puerto Rico. Wind shear, dry air, and cold air temperatures will keep any development of this system to a minimum. A large cloud of African dust over the eastern Atlantic should keep things quiet there the rest of the week. There are no indications that Beryl's formation presages the beginning of a more active period in the Atlantic. Wind shear is expected to remain seasonably high for the rest of July, and none of the computer models are hinting at any development over the next week.

I'll be back with an update Thursday morning.

Jeff Masters

Updated: 8:43 PM GMT on July 19, 2006

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Beryl intensifying

By: JeffMasters, 1:26 PM GMT on July 19, 2006

Tropical Storm Beryl spent the night looking pretty ragged, but is starting to put on a burst of intensification. This morning's Hurricane Hunter aircraft just left the storm, and reported a central pressure of 1004 mb at 8am EDT, down 1 mb from the previous advisory. The plane found winds as high as 52 knots (60 mph) at 5,000 foot altitude, which corresponds to about 50 mph at the surface--a 5 mph increase from the 5am advisory. Satellite imagery shows a large blow-up of thunderstorms with very cold tops on the southwest side of Beryl. These cold tops mean the thunderstorms are reaching high levels of the atmosphere, and are therefore very intense.

If we examine the sea surface temperature plot for this morning (Figure 1), we see that Beryl has just started crossing the axis of the warmest waters of the Gulf Stream. These warm 27 - 28 C waters are probably responsible for the current burst of intensification. Beryl is moving north and should stay over these warmer waters until tonight, so we can expect continued intensification today. Once Beryl gets north of the Virginia/Maryland border, SSTs cool rapidly, and intensification should cease. Wind shear is currently 5 - 10 knots, which is low enough to allow intensification. Beryl will probably not spend enough time over these warm waters to make it to hurricane status, but New England may have a strong tropical storm with 60 mph winds on its doorstep Friday. Note, however, that the two primary intensity forecast models used by NHC--the GFDL and SHIPS--predict that Beryl will only be a weak tropical storm with 45 mph winds on Friday when it approaches New England.


Figure 1. 3D image of sea surface temperatures for July 19, 2006. Beryl is headed due north across the warmest waters of the Gulf Stream current today. Image credit: NOAA Environmental Modeling Center.

Beryl is expected to continue moving north today, then turn more to the northeast on Thursday as a trough of low pressure approaches from the west. Just how strong this trough is will determine how close Beryl passes to New England. Some of the forecast models are forecasting a strike on Long Island or Cape Cod Friday, but the official NHC forecast of a turn out to sea just south of New England sounds more reasonable, given that no July tropical storm --and only one July hurricane (1916)--has ever made landfall in New England.

Elsewhere in the tropics
The rest of the tropical Atlantic is quiet today. A large cloud of African dust has just pushed off the coast of Africa, which should keep things quiet over the eastern Atlantic the rest of the week. There are no indications that Beryl's formation presages the beginning of a more active period in the Atlantic. Wind shear is expected to remain seasonably high for the rest of July, and none of the computer models are hinting at any development over the next week.

There will not be a Hurricane Hunter aircraft in Beryl until 2pm EDT. I'll be back with an update around 4pm today when the aircraft has had time to sample the storm.

Jeff Masters

Updated: 1:35 PM GMT on July 19, 2006

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Tropical Storm Beryl arrives

By: JeffMasters, 8:58 PM GMT on July 18, 2006

A hurricane hunter airplane found flight level winds of 46 knots (53 mph) at 1000 feet altitude in TD 2, and 40 mph winds at the surface, so this is now Tropical Storm Beryl. As one can gather from the decoded recco reports we now make available, the aircraft has made two passes through the storm. The lowest central pressure was 1007 mb, which is 1 mb lower than the 5pm advisory from NHC.

Upper level winds from the northwest are keeping thunderstorm activity limited on the storm's west side. However, wind shear has decreased from 10-15 knots this morning to 5-10 knots this afternoon. This decrease in wind shear has allowed some thunderstorms to wrap around to the north side of the storm, and the storm is now attempting to wrap deep convection (large thunderstorms) all the way around its center.

Water temperatures are 26 - 28C in the storm's vicinity, which is above the 26C threshold needed for tropical storm formation. The axis of the warm Gulf Stream current lies just 100 miles to the storm's northwest, so NHC's forecast of a more north-northwesterly motion towards the North Carolina coast will bring the system over very deep warm waters of 28 - 29C that should aid in intensification. The GFS computer model is indicating that wind shear will remain in the 5 - 10 knot range the next few days, which is low enough to allow some modest intensification, as well. The storm may suck in some dry air from over the continent which may inhibit development, however. A Category 1 hurricane is certainly a good possibility by Thursday morning, as the storm should stay over the warm waters of the Gulf Stream until then. Once the storm gets north of Cape Hatteras North Carolina, the chances for continued intensification lessen, since water temperatures are in the 70s close to the coast.

As we can see from the historical plot of the 15 tropical cyclones to form in July and August off the Carolina coast in July and August (Figure 2), only one hit land, and only two got as strong as a Category Two hurricane. If this storm does hit land, it will definitely buck the historical trend. North Carolina, Virgina, Maryland, and Nova Scotia appear to be the only land areas at risk from this storm.


Figure 1. Latest satellite of Tropical Depression Two.


Figure 2. Historical tracks of tropical cyclones that formed off the Carolina coast in July and August.

Elsewhere in the tropics
An area of thunderstorms a few hundred miles northeast of Puerto Rico is associated with a tropical wave interacting with an upper-level low pressure system. Although wind shear has dropped to 10 knots, there is a lot of dry air around, and the system is very disorganized. No tropical development of this system should occur through Wednesday as it tracks northwest at 15 mph towards Bermuda.

A large tropical wave is 300 miles southwest of the Cape Verde Islands. Water temperatures are marginal for tropical development in this region, and wind shear is high, 10-30 knots. The wind shear forecast shows the possibility of more favorable conditions later in the week if the wave can hold together as it moves westward across the Atlantic at 15-20 mph.

Jeff Masters

Updated: 8:59 PM GMT on July 18, 2006

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TD 2 intensifying

By: JeffMasters, 8:04 PM GMT on July 18, 2006

A hurricane hunter airplane is currently in Tropical Depression Two at 600 - 900 feet in altitude. As one can gather from the decoded recco reports we now make available, the aircraft has made one pass through the storm from SW to NE, and measured strongest surface winds of 28 mph in the northeast quadrant. The lowest central pressure was 1008 mb, which is 3 mb lower than the 2pm advisory from NHC. The airplane put out a vortex report at 3:15 pm EDT, which said that they found strongest winds of 35 mph at the surface. So, this is still a tropical depression--we need winds of at least 39 mph at the surface to have a tropical storm.

Upper level winds from the northwest are keeping thunderstorm activity limited on the storm's west side. However, wind shear has decreased from 10-15 knots this morning to 5-10 knots this afternoon. This decrease in wind shear has allowed some thunderstorms to wrap around to the north side of the storm, and the storm is now attempting to wrap deep convection (large thunderstorms) all the way around its center. Given the improving satellite presentation and the low central pressure found by the hurricane hunters, I expect that this will be Tropical Storm Beryl by midnight.

Water temperatures are 26 - 28C in the storm's vicinity, which is above the 26C threshold needed for tropical storm formation. The axis of the warm Gulf Stream current lies just 100 miles to the storm's northwest, so NHC's forecast of a more northwesterly motion towards the North Carolina coast will bring the system over very deep warm waters of 28 - 29C that should aid in intensification. The GFS computer model is indicating that wind shear will remain in the 5 - 20 knot range the next few days, which is low enough to allow some modest intensification, as well. The exact magnitude of this shear will be critical in determining how strong this storm gets, and is difficult to predict at this time. A Category 1 hurricane is certainly a good possibility by Thursday morning, as the storm should stay over the warm waters of the Gulf Stream until then. Once the storm gets north of Cape Hatteras North Carolina, the chances for continued intensification lessen, since water temperatures are in the 70s close to the coast.

As we can see from the historical plot of the 15 tropical cyclones to form in July and August off the Carolina coast in July and August (Figure 2), only one hit land, and only two got as strong as a Category Two hurricane. If this storm does hit land, it will definitely buck the historical trend. North Carolina, Virgina, Maryland, and Nova Scotia appear to be the only land areas at risk from this storm.


Figure 1. Latest satellite of Tropical Depression Two.


Figure 2. Historical tracks of tropical cyclones that formed off the Carolina coast in July and August.

Elsewhere in the tropics
An area of thunderstorms a few hundred miles northeast of Puerto Rico is associated with a tropical wave interacting with an upper-level low pressure system. Although wind shear has dropped to 10 knots, there is a lot of dry air around, and the system is very disorganized. No tropical development of this system should occur through Wednesday as it tracks northwest at 15 mph towards Bermuda.

A large tropical wave is 300 miles southwest of the Cape Verde Islands. Water temperatures are marginal for tropical development in this region, and wind shear is high, 10-30 knots. The wind shear forecast shows the possibility of more favorable conditions later in the week if the wave can hold together as it moves westward across the Atlantic at 15-20 mph.

Jeff Masters

Updated: 8:48 PM GMT on July 18, 2006

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Tropical Depression Two here?

By: JeffMasters, 1:09 PM GMT on July 18, 2006

The National Hurricane Center issued this special advisory at 8:20am EDT this morning:

Satellite and surface observations this morning indicate the low pressure area located about 250 miles southeast of North Carolina coast has become better organized this morning... and a tropical depression may be forming. An Air Force Reserve reconnaissance aircraft is scheduled to investigate the system this afternoon. Interests along the North Carolina and Virginia coasts should closely monitor the progress of this system.

Indeed, the first visible satellite images from this morning show a clear surface circulation developing near 32N 74W, about 250 miles south-southeast of Cape Hatteras, North Carolina. There is an impressive area of thunderstorms to the southeast side of the center of circulation. Upper level winds of 10-15 knots from the northwest are keeping any thunderstorms from building on the northwest side of the disturbance.

Water temperatures are 26 - 28C in the storm's vicinity, which is above the 26C threshold needed for tropical storm formation. The axis of the warm Gulf Stream current lies just 100 miles to the storm's northwest, so any motion towards the North Carolina coast will bring the system over very deep warm waters of 28 - 29C that should aid in intensification. The GFS computer model is indicating that wind shear will remain in the 5 - 20 knot range the next few days, which is low enough to allow some modest intensification. The exact magnitude of this shear will be critical in determining how strong this storm gets, and is difficult to predict at this time.

As we can see from the historical plot of the 15 tropical cyclones to form in July and August off the Carolina coast in July and August (Figure 3), all these systems moved north or northeast out to sea. Only one hit land, and only two got as strong as a Category Two hurricane. This storm will follow the historical trend, as a strong trough of low pressure is expected to push off the East Coast by Thursday, turning the disturbance northwards and then recurving it out to sea. North Carolina, Virgina, Maryland, and Nova Scotia appear to be the only land areas at risk from this storm.


Figure 1. Latest satellite image of the Southeast Coast disturbance.


Figure 2. Preliminary forecast model tracks for the Southeast Coast disturbance.


Figure 3. Historical tracks of tropical cyclones that formed off the Carolina coast in July and August.

Elsewhere in the tropics
A large area of thunderstorms is a few hundred miles northeast of Puerto Rico. This is associated with a tropical wave interacting with an upper-level low pressure system. Wind shear has dropped to 10 - 25 knots over this area, which is still too high to allow tropical development today, as there is a large amount of dry air in the vicinity. The system is expected to track northwest towards Bermuda and recurve out to sea.

A somewhat ragged tropical wave is near Africa, just south of the Cape Verde Islands. Water temperatures are marginal for tropical development in this region, and wind shear is high, 10-30 knots. The wind shear forecast shows the possibility of more favorable conditions later in the week if the wave can hold together as it moves westward across the Atlantic at 15-20 mph. I'm not expecting this to happen, however.

The Hurricane Center has scheduled a reconnaissance aircraft to check the Carolinas system out at 2pm EDT today. I'll be back with an update when the plane has had a chance to check the storm out.

Jeff Masters

Updated: 1:18 PM GMT on July 18, 2006

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Southeast U.S. development

By: JeffMasters, 6:25 PM GMT on July 17, 2006

The tail end of an old cold front over the waters off the Southeast U.S. coast could serve as the focus for some tropical development over the next few days. Some impressive thunderstorms are developing over the waters due east of Georgia, thanks to a narrow area of reduced wind shear of 5-10 knots that has developed here. The GFS computer model is indicating that this reduced shear will remain for the next few days, and the Hurricane Center has scheduled a reconnaissance aircraft to check the system out on Tuesday at 2pm EDT, if needed. The system is over the warm Gulf Stream waters, where sea surface temperatures are very favorable for development, 28-30 C. The system is still pretty disorganized, although the latest visible imagery is hinting at a surface circulation. I believe that the earliest a tropical depression would form is Wednesday.

Steering currents are weak, so it is difficult to tell where this system might go. A strong trough of low pressure is expected to push off the East Coast by Wednesday, so this may turn the disturbance northwards and recurve it out to sea. However, it's quite possible the trough will not be strong enough to grab the disturbance, which will wander about off the Carolina coast for most of the week.


Figure 1. Latest satellite image of the Southeast Coast disturbance.


Figure 2. Preliminary forecast model tracks for the SOutheast Coast disturbance.

A very large area of concentrated thunderstorms is a few hundred miles northeast of Puerto Rico. This is associated with a tropical wave interacting with an upper-level low pressure system. Wind shear is 20 - 30 knots over this area, and no tropical development is expected. We will have to watch this area later in the week as it approaches the East Coast, but it appears now that wind shear will remain too high to allow development.

An extratropical or subtropical low is about 220 miles south-southeast of southwestern Nova Scotia, and is moving northeast away from the U.S. at 20 mph. The storm is over the Gulf Stream where water temperatures are in the upper 70s, which is borderline for a tropical storm. The low has a large area of heavy thunderstorms on the northeast side of the center of circulation, and is undergoing significant wind shear that is exposing the center. This storm is not a threat to develop into a tropical storm, since the waters in front of it are too cool to allow tropical development.

>
Figure 3. Visible satellite image for 8am EDT July 17 2006, showing the various areas of interest along the East Coast.

A solid-looking tropical wave has just emerged off the coast of Africa, and is headed towards the Cape Verde Islands at 15-20 mph. Water temperatures are marginal for tropical development in this region, wind shear is high, 10-30 knots. I'm not expecting this wave to be a threat, even though the wind shear forecast shows wind shear dropping tomorrow. It's very common this time of year to see impressive looking waves come off the coast of Africa, only to fizzle after spending a day over the water. If the wave is still holding togther by this time tomorrow, I'll take it seriously. But I think we need another two weeks for the waters to warm before these African waves will bear watching.

Jeff Masters

Updated: 6:41 PM GMT on July 17, 2006

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Developments off the U.S East Coast

By: JeffMasters, 1:12 PM GMT on July 17, 2006

A cold front that pushed off the U.S. East Coast this weekend stalled out, and has spawned two areas of low pressure. The first is an extratropical or subtropical low that developed along the north portion of the front. This low is about 300 miles east-southeast of Cape Cod, Massachusetts, and is moving northeast away from the U.S. The storm is over the Gulf Stream where water temperatures are in the upper 70s, which is borderline for a tropical storm. The low has a large area of heavy thunderstorms on the northeast side of the center of circulation, and is undergoing significant wind shear that is exposing the center. To my eye, the system is probably a subtropical storm, and technically should be classified as Subtropical Depression Two. However, is it difficult to tell for sure, and the NHC is conservatively not naming it, since it is headed towards colder water and has little chance of becoming a full tropical storm.

>
Figure 1. Visible satellite image for 8am EDT July 17 2006, showing the various areas of interest along the East Coast.

The departing low has left behind the tail end of the old cold front over the waters off the South Carolina/North Carolina coast. This old front could serve as the focus for some tropical development over the next few days. There is a narrow area of reduced wind shear of 10-15 knots over this region, and the GFS computer model is indicating that the area of reduced shear will remain. Steering currents are weak, so it is difficult to tell where this system might go. The models seem to lean towards it heading northeast up the coast, possibly brushing Cape Hatteras and Nova Scotia later in the week. However, the system is currently very broad and disorganized, and any development will be slow to occur.

A very large area of concentrated thunderstorms is a few hundred miles north of Puerto Rico. This is associated with a tropical wave interacting with an upper-level low pressure system. Wind shear is 25-35 knots over this area, and no tropical development is expected. We will have to watch this area later in the week as it approaches the East Coast, as wind shear may fall and allow some slow development.

A solid-looking tropical wave has just emerged off the coast of Africa, and is headed towards the Cape Verde Islands at 15-20 mph. Water temperatures and wind shear are marginal for tropical development in this region, and I'm not expecting this wave to be a threat. It's very common this time of year to see impressive looking waves come off the coast of Africa, only to fizzle after spending a day over the water. By early August, I'll start taking these waves more seriously, when the waters are a bit warmer.

Jeff Masters

Updated: 3:15 PM GMT on July 17, 2006

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Developments off the U.S East Coast

By: JeffMasters, 10:53 PM GMT on July 16, 2006

A cold front that pushed off the U.S. East Coast this weekend and stalled out has created an interesting situation to watch. An extratropical or subtropical low has developed along the north portion of the front, about 300 miles southeast of Cape Cod, Massachusetts. Water temperatures are right at the borderline for a tropical storm--about 80 Fahrenheit--so this low is unlikely to develop into a tropical storm as it heads northeast out to sea towards colder water. The low has a large area of heavy thunderstorms on the southeast side of the center of circulation, well removed from the center. This is characteristic of a subtropical storm experiencing significant wind shear. This is the expected development I was referring to this morning in my blog.


Figure 1. Current satellite image of the U.S. East Coast.

The departing low has left behind the tail end of the old cold front over the waters off the South Carolina/North Carolina coast. This old front could serve as the focus for some tropical development over the next few days. Already, some tropical-looking thunderstorms have built over the front, in a narrow area of reduced wind shear of 5-10 knots that has developed. The GFS computer model is indicating that the area of reduced shear will remain. Steering currents are weak, so it is difficult to tell where this tropical blob might go. The models seem to lean towards this system heading northeast up the coast, possibly brushing Cape Hatteras and Nova Scotia later in the week.

Wind shear visualized
I've linked a photo of an odd fog formation a wunderphotographer in Alaska took--I've never seen anything like this photo! It shows very graphically what strong wind shear can do to contort a cloud into strange shapes. The wind speed and direction are different at the bottom of this fog bank than at the top, creating a twisting, shearing effect on the cloud that bends it into strange shapes. Now imagine what strong wind shear can do to a developing tropical depression--ouch!

Jeff Masters

Updated: 12:04 PM GMT on July 17, 2006

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A quiet Sunday in the tropics

By: JeffMasters, 2:55 PM GMT on July 16, 2006

It's another quiet Sunday for the tropical Atlantic. The impressive line of thunderstorms brewing off the coast of the Carolinas is associated with a cold front. An extratropical or subtropical low pressure system is expected to form along this front by Monday, then push slowly up the East Coast during the week. This system is not a threat to become a tropical storm today--there's too much wind shear, cold air, and cool water. However, the Hurricane Center is giving it the chance of slowly acquiring tropical characteristics if it can remain south of Cape Hatteras, North Carolina for the next two days.

Wind shear is a very high 20 - 40 knots across most of the Caribbean and Gulf of Mexico. Shear is expected to stay high in these regions for at least the next six days, and none of the reliable computer models are forecasting tropical storm formation in the Atlantic during this period. Enjoy the quiet time!

I've linked a photo of an odd fog formation a wunderphotographer in Alaska took--I've never seen anything like this photo! It shows very graphically what strong wind shear can do to contort a cloud into strange shapes. The wind speed and direction are different at the bottom of this fog bank than at the top, creating a twisting, shearing effect on the cloud that bends it into strange shapes. Now imagine what strong wind shear can do to a developing tropical depression--ouch!

Jeff Masters

Updated: 4:30 PM GMT on July 16, 2006

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Shear rules!

By: JeffMasters, 1:58 PM GMT on July 15, 2006

It's another quiet weekend for the tropical Atlantic. A storm brewing off the coast of North Carolina is extratropical, and will move northeastward out to sea. An area of showers pushing ashore into Nicaragua and Honduras is associated with a tropical wave. Wind shear is high, and no development is expected. Wind shear is a very high 20 - 40 knots across the entire Caribbean, and most of the Gulf of Mexico. Shear is expected to stay high in these regions for at least the next five days, according to the GFS model. None of the reliable computer models are forecasting tropical storm formation in the Atlantic during the next six days. Shear rules!

Jeff Masters

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Field Notes from a Catastrophe book review

By: JeffMasters, 12:43 PM GMT on July 14, 2006

Elizabeth Kolbert is a writer for the New Yorker magazine. A three-part series she wrote for the magazine in 2005 has been converted into a short, well-researched, and very readable book on climate change called, "Field Notes from a Catastrophe" ($15 from amazon.com). The science presented is excellent, and I couldn't find any errors. Kolbert visits leading climate change scientists in the field, spending time in the Arctic, Greenland, Dr. James Hansen's laboratory, and in United Nations climate change meetings. We get to see the science the way these scientists see it, which is a very powerful way to emphasize the major climate changes that are already underway on our planet.

Kolbert delivers a memorable description of a visit to Alaska, where record temperatures have begun melting permafrost that formed at the beginning of the last ice age, 120,000 years ago. She visits the remote island of Sarichef, five miles off the coast of the Seward Peninsula. A subsistence hunting village has existed there for centuries. However, the entire population of 591 must be relocated to the mainland because the island is eroding away. The problem? Lack of the customary sea ice in the fall has allowed storm surges from the powerful storms that hit during that season to push far inland. Kolbert talks to an Inuit hunter named John Keogak, who lives in Canada's Northwest Territories, 500 miles north of the Arctic circle. He and his fellow hunters started seeing robins for the first time a few years ago. The Inuits have no word for the bird in their language. Kolbert travels to "drunken forests" where the trees lean at crazy angles due to the collapse of the permafrost beneath. In one of many of the odd and amusing observations the book is sprinkled with, she writes:

A few blocks beyond the drunken forest, we came to a house where the front yard showed clear signs of ice wedge melt-off. The owner, trying to make the best of things, had turned the yard into a miniature golf course.

As the title implies, this is not a cheerful book, and Kolbert paints a gloomy picture of the how climate change is affecting the planet. I highly recommend the book for those interested in reading about climate change. Three and a half stars.

Jeff Masters

Book and Movie Reviews

Updated: 12:01 AM GMT on August 16, 2011

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New wave off Africa ; New Orleans levees on hold

By: JeffMasters, 7:09 PM GMT on July 13, 2006

A new area of concern has developed today off of the coast of Africa, 300 miles south-southwest of the Cape Verde Islands, at about 12N 25W. This large and well-organized tropical wave has developed a surface circulation, and is beginning to show some intense thunderstorms developing near its center. Wind shear is a marginal 10-20 knots over the wave, but is forecast to remain at this level or decrease some over the next two days. Sea surface temperatures are marginal for development, about 26-27 degrees C. There is some African dust to the wave's north, but not as much as we've been seeing in previous weeks. This wave could slowly organize into a tropical depression in the next day or two as it moves west-northwest at 15-20 mph. It's too early to speculate what the long-term track of this system might be. NHC is not impressed with this wave; they have not mentioned it in their 5:30 pm tropical outlook. No doubt the marginal SSTs and moderate wind shear--plus the fact that systems in this vicinity generally do not start developing until early August--are giving them a wait-and-see attitude.


Figure 1. Visible image of the Cape Verdes tropical wave. image credit: Navy Research Lab. Try animating this image from their web site to watch the wave spin up, and see the interesting eddies downwind of the islands off the coast of Africa.

Gulf of Mexico
Thunderstorms in the Gulf of Mexico near Key West, associated with a westward moving tropical wave, have decreased since this morning. Surface pressures are not falling, and no computer models are predicting that this area will be a future threat. However, wind shear is low enough to permit some slow development of this disturbance over the next day or two, so we'll have to keep an eye on it.


Figure 2. Latest satellite image of the Gulf of Mexico.

An upper level low pressure system is spinning over the western Gulf of Mexico. This low is expected to move ashore over Mexico by Friday without any tropical development occurring.

A tropical wave that moved through the Lesser Antilles Wednesday is in the eastern Caribbean. The wave has limited thunderstorm activty, and there is high wind shear and plenty of dry air in the eastern Caribbean. Development of this wave is unlikely.

Update on New Orleans flood protection
The Army Corps of Engineers has missed a July 9 deadline to complete new floodgates at the Lake Pontchartrain entrance to one of the drainage canals that flooded New Orleans during Katrina. No revised date has been set for the completion of the project. If a storm were to come now, the Army Corps would close off the canals using sheet pilings, as they did during Hurricane Rita. The new gates are designed to be closed when a hurricane threatens to bring a storm surge over five feet, and thereby keep waters from Lake Pontchartrain from flowing deep into the city along the drainage canals. It was the failure of the levees along these drainage canals that primarily responsible for the flooding of New Orleans during Katrina. However, closing the drainage canals means that the city will flood due to excessive rains, since it is these canals that take all the rainwater out of the below sea level areas of the city and dumps it into the Lake. (Thanks to wundermember mrpember for posting this info).

New Army Corps of Engineers report issued (repeat from this morning's blog)
A long awaited Army Corps of Engineers report on Louisiana coastal protection and restoration came out this week. The report had no specific recommendations on immediate actions to take to protect New Orleans from the next hurricane, saying another 18 months was needed to study the problem. Politicians and scientists immediately criticized the plan, saying that action is needed now. In particular, Governor Blanco of Louisiana and Louisiana's Senators were upset that five specific recommendations that they had agreed on with the Corps in May were stripped out of the proposal:

-- Beginning design work on a barrier and gate plan to protect the New Orleans area from major hurricanes.

-- Closing the Mississippi River-Gulf Outlet (MR-GO) to major ship traffic and beginning environmental restoration of the wetlands adjacent to it.

-- Design work on a plan for rebuilding eroded barrier islands and headlands and building new ones in the Barataria basin, which includes parts of Jefferson, Lafourche and Terrebonne parishes.

-- Authorizing the Morganza-to-Gulf hurricane levee project that stretches along much of the same area and has been awaiting congressional approval for several years.

-- Approval and financing for a variety of smaller restoration projects in southwestern Louisiana.

"These critical projects cannot wait another 18 months to be considered for action by Congress," Blanco said in a statement released Monday.

In the report, the Corps say they have completed emergency repairs to 169 miles of New Orleans levees, which are now as strong or stronger than before Hurricane Katrina. I can't tell from news reports what levee work--if any--is currently going on, I'd be interested to see if any of you know. In particular, is the $3 billion plan to move the pumping stations on the 17th Street Canal and London Avenue Canal to Lake Pontchartrain being worked on? It seems to me that this work is the most critical flood protection measure that needs to be undertaken.

Jeff Masters

Updated: 9:42 PM GMT on July 13, 2006

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Gulf of Mexico disturbance; New Orleans levee plan released

By: JeffMasters, 1:09 PM GMT on July 13, 2006

The main area of concern today is a tropical wave off of the west coast of Florida that is kicking off some heavy thunderstorms over the waters surrounding Key West. Wind shear is low enough to permit some slow development of this disturbance over the next day or two as it moves westward or west-northwestward across the Gulf of Mexico at 10 mph. However, the area of thunderstorms is of limited size, surface pressures are not falling, and there are no signs that this area may be a future threat.


Figure 1. Latest satellite image of the Gulf of Mexico.

An upper level low pressure system is spinning over the western Gulf of Mexico. This low is expected to move ashore over Mexico by Friday without any tropical development occurring.

A tropical wave that moved through the Lesser Antilles Wednesday is in the eastern Caribbean. The wave has limited thunderstorm activty, and there is high wind shear and plenty of dry air in the eastern Caribbean. Development of this wave is unlikely.

The three computer models best at forecasting tropical storm formation (GFS, UKMET, NOGAPS) are all predicting no tropical storm formation in the Atlantic for the next six days. Wind shear is forecast to remain high during this period, then begin a slow decrease through the end of July.

New Orleans flood protection on hold
A long awaited Army Corps of Engineers report on Louisiana coastal protection and restoration came out this week. The report had no specific recommendations on immediate actions to take to protect New Orleans from the next hurricane, saying another 18 months was needed to study the problem. Politicians and scientists immediately criticized the plan, saying that action is needed now. In particular, Governor Blanco of Louisiana and Louisiana's Senators were upset that five specific recommendations that they had agreed on with the Corps in May were stripped out of the proposal:

-- Beginning design work on a barrier and gate plan to protect the New Orleans area from major hurricanes.

-- Closing the Mississippi River-Gulf Outlet (MR-GO) to major ship traffic and beginning environmental restoration of the wetlands adjacent to it.

-- Design work on a plan for rebuilding eroded barrier islands and headlands and building new ones in the Barataria basin, which includes parts of Jefferson, Lafourche and Terrebonne parishes.

-- Authorizing the Morganza-to-Gulf hurricane levee project that stretches along much of the same area and has been awaiting congressional approval for several years.

-- Approval and financing for a variety of smaller restoration projects in southwestern Louisiana.

"These critical projects cannot wait another 18 months to be considered for action by Congress," Blanco said in a statement released Monday.

In the report, the Corps say they have completed emergency repairs to 169 miles of New Orleans levees, which are now as strong or stronger than before Hurricane Katrina. I can't tell from news reports what levee work--if any--is currently going on, I'd be interested to see if any of you know. In particular, is the $3 billion plan to move the pumping stations on the 17th Street Canal and London Avenue Canal to Lake Pontchartrain being worked on? It seems to me that this work is the most critical flood protection measure that needs to be undertaken.

I'll be back with an update this afternoon on the Gulf of Mexico system.

Jeff Masters

Updated: 1:18 PM GMT on July 13, 2006

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Barbados tropical wave falls apart

By: JeffMasters, 8:35 PM GMT on July 12, 2006

A tropical wave over Barbados has fallen apart this afternoon after briefly organizing this morning. Strong upper-level winds from the west have disrupted the heavy thunderstorm activity that had built to the east of the system. This wind shear was analyzed at about 20 knots at 2pm EDT by the University of Wisconsin CIMSS wind shear page.

The system is moving west at 15-20 mph, and brought wind gusts of 28 mph Barbados this afternoon. St. Lucia will get some gusty winds tonight. Rainfall in these islands will be spotty, since there is very little thunderstorm activity remaining. Thunderstorm activity could re-build tonight or Thursday morning, but the presence of high wind shear to the north and west will likely keep this system from ever developing into a tropical depression.


Figure 1. Latest satellite image of the tropical wave moving through the Lesser Antilles Islands.


Figure 2. Model forecast tracks for the tropical wave moving through the Lesser Antilles Islands.

The rest of the tropical Atlantic is quiet. A tropical wave is pushing ashore into South Florida, and will bring heavy rains there. An upper-level low is spinning over the central Gulf of Mexico, but this low is not expected to develop, due to high wind shear. None of the major computer models are forecasting any tropical storm formation in the Atlantic for the next six days. Wind shear is forecast to remain high over most of the tropical Atlantic this week, then gradually decrease for the remainder of the month.

Jeff Masters

Updated: 8:37 PM GMT on July 12, 2006

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Barbados tropical wave better organized

By: JeffMasters, 1:10 PM GMT on July 12, 2006

A tropical wave about 150 miles east of Barbados has become better organized this morning. A sudden burst of intense thunderstorms developed between 6am and 10am EDT, and a surface circulation is now apparent near 12.5N 57W on visible satellite imagery. The center is exposed on the west side due to strong upper-level winds from the west, and the latest 8am EDT winds shear analysis from the University of Wisconsin showed wind shear of 10-20 knots over the disturbance. Weaker upper-level winds just to the disturbance's south have pushed northwards, creating an opportunity for the system to develop. (The University of Wisconsin wind shear product is updated every three hours, and the 11am EDT analysis is due out around 1 pm EDT).

The system is moving west at 15 mph, and should bring heavy rain and wind gusts of 30-40 mph to Barbados this afternoon and St. Vincent and St. Lucia tonight. It will be very interesting to see what the wind and pressure readings look like from these islands today. It's possible that this system will become a tropical depression later today, but I doubt that it will make it to tropical storm status, despite its healthier appearance on satellite imagery this morning. The area covered by intense thunderstorms is very small, and it would take only a modest increase in wind shear to tear the system apart. There's plenty of wind shear to the system's north and west, and the chances of it surviving beyond Thursday are low.


Figure 1. Latest satellite image of the tropical wave approaching the Lesser Antilles Islands.


Figure 2. Model forecast tracks for the tropical wave approaching the Lesser Antilles Islands.

The rest of the tropics are quiet. A tropical wave is pushing ashore into South Florida, and will bring heavy rains there. An upper-level low is spinning over the central Gulf of Mexico, but this low is not expected to develop, due to high wind shear. None of the major computer models are forecasting any tropical storm formation in the Atlantic for the next six days. Wind shear is forecast to remain high over most of the tropical Atlantic this week, then gradually decrease for the remainder of the month.

I'll have an update on the Barbados system this afternoon.

Jeff Masters

Updated: 3:31 PM GMT on July 12, 2006

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The tropics are quiet today

By: JeffMasters, 2:08 PM GMT on July 11, 2006

A tropical wave near 13N 52W, about 600 miles east of the Lesser Antilles Islands, has minimal thunderstorm activity today, and is not expected to develop. Strong upper-level winds of 20-30 knots are creating too much wind shear.

The well-defined circulation visible on satellite imagery over the southeast Gulf of Mexico is a cold-cored upper level low pressure system. Wind shear is high, and no development is expected as it moves slowly southwest.

An area of disturbed weather over the Bahama Islands is associated with a tropical wave, and is interacting with the upper level low in the Gulf and a second upper level low north of the Bahamas. No significant development of this area is expected before it moves ashore into Florida on Wednesday. Portions of Florida should get some heavy rains from this system.


Figure 1. Latest satellite image of the tropical wave approaching the Lesser Antilles Islands.


Figure 2. Model forecast tracks for the tropical wave approaching the Lesser Antilles Islands.

The rest of the tropics are quiet. Wind shear is forecast to remain high over most of the tropics through Thursday, and none of the four major global computer models are hinting at tropical storm development in the Atlantic. By Friday, wind shear is expected to decrease sharply over the Gulf of Mexico, so we'll have to keep an eye on that region this weekend.

Jeff Masters

Updated: 2:36 PM GMT on July 11, 2006

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A normal July in the tropics?

By: JeffMasters, 1:56 PM GMT on July 10, 2006

A tropical wave about 900 miles east of the Lesser Antilles Islands has become much less organized since this morning. Strong upper-level winds just to the system's north have disrupted it, and its west-northwestward track should take it deeper into this area of high shear. I don't expect any development from this wave. There is some deep thunderstorm activity to the southwest of this wave, near 9N 52W, that is not undergoing as much shear. However, this area is disorganized, and I don't expect any development here, either.

The other area of interest today and a large area of deep thunderstorms stretching from Puerto Rico to the southeastern Bahama Islands. These showers are associated with a cold-cored upper-level low pressure system that is moving slowing west-northwestward. Any development of this area will be slow, due to wind shear, high surface pressures, and dry air. This disturbance should move over Florida on Wednesday, bringing heavy rain to portions of the state.


Figure 1. Latest satellite image of the tropical wave approaching the Lesser Antilles Islands.


Figure 1. Model forecast tracks for the tropical wave approaching the Lesser Antilles Islands.

A normal July?
Will July 2006 be a normal July for the Atlantic hurricane season? First, we need to look at what constitutes a normal July. As we can see from the Atlantic hurricane frequency graph in Figure 3, July is typically a very quiet month, almost as quiet as June is. It's usually not until the second week of August that hurricane season really starts to heat up. Since the current active Atlantic hurricane period began in 1995, there have been an average of about 1.5 named storms and 0.8 hurricanes per July. It's common to go several years in a row without getting a July tropical storm, as happened in 1999-2001. Last year's five named storms in July--including three hurricanes, two of them major hurricanes--was definitely an extremely unusual year. By this time last year, we were already on our fourth named storm, and Category 4 Hurricane Dennis was churning its way through the Caribbean.


Figure 3. The curve of historical normal hurricane activity of the Atlantic Ocean.

Why is July usually so quiet?
Sea Surface Temperatures right now (Figure 4) are warm enough to support tropical storm formation throughout the Gulf of Mexico, Bahamas, and the Main Development Region (MDR) of the Atlantic (the MDR is the region between 10N and 20N, and includes the Caribbean Sea). The only part of the MDR still too cool to support tropical storms is the far eastern Atlantic off the coast of Africa. SSTs generally do not get warm enough to support the classic intense "Cape Varde" hurricanes that form off the coast of Africa until mid-August in this region. Thus, we should not expect any Cape Verdes type hurricanes until August.


Figure 4. Atlantic SSTs for July 4, 2006. Blue colors represent SSTs colder than 26 C (80 F), which are too cool to support tropical storm formation.

Since SSTs are not the limiting factor, our old friend wind shear must be the answer! Let's look at wind shear in the eastern Caribbean, where both Hurricane Dennis and Hurricane Emily intensified into major hurricanes last year. As we can see from Figure 5, wind shear was very low in this region in 2005, and has been near normal or even above normal in 2006. Wind shear is expected to remain near average or above average across the the entire tropical Atlantic for the remainder of this week. While it is possible a tropical storm could form in a "hole" in the wind shear, the chances of it being able to stay together for an extended period and grow into a hurricane are low. So, it appears that the first half of July is shaping up to be a very normal one in the tropics.

What about the last half of July?
The two-week forecast from the GFS computer model has been consistently predicting a steady reduction in the amount of wind shear over the tropical Atlantic for the week of July 15 - July 23. Thus, many more "holes" in the wind shear will be opening up, potentially allowing tropical storms to form. I'll stick with my prediction I made at the end of June that we'll see one or two named storms in July, one of which may be a hurricane (but not a major hurricane). The forecast pressure pattern for the rest of July continues to show a weakness in the Bermuda High near the U.S. East Coast. This favors an above-normal chance of strikes on the U.S. East Coast, and a below-normal chance for the Gulf Coast, for storms forming in the Caribbean or near the Bahama Islands.


Figure 5. Wind shear over the Eastern Caribbean in 2005 (red line) and 2006 (blue line) compared to normal (black line). Wind shear is computed as the difference in wind between the upper atmosphere (200 mb pressure, about 40,000 feet high) and lower atmosphere (850 mb pressure, about 5,000 feet high). Image credit: CIRA

Jeff Masters

Updated: 6:11 PM GMT on July 10, 2006

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Two minor disturbances in the tropics today

By: JeffMasters, 3:05 PM GMT on July 09, 2006

Two areas in the tropics bear mentioning today, but the long range chances of either of these disturbances developing into a tropical storm are low. The first area is associated with a cold-cored upper level low pressure system north of Puerto Rico and east of the Bahama Islands. A tropical wave is passing through the area as well, and the combination is producing heavy thunderstorms and gusty winds over a large area of ocean. This activity will move slowly northwest over the next few days, but wind shear--currently 10 to 20 knots over the region--is expected to increase, keeping this system from developing.

A large tropical wave about 1300 miles east of the Lesser Antilles Islands is moving west-northwest at about 15-20 mph. Wind shear has dropped to 5-15 knots over a large region surrounding the wave, and some slow development is possible today and Monday. However, wind shear is forecast to increase sharply in the wave's vicinity on Tuesday, and the wave is pushing northward into an large area of dry air and African dust. These factors make the longer-term growth of this wave doubtful.

High wind shear will continue over the Gulf of Mexico for the next few days, so I don't expect any development there, and the rest of the tropics are quiet.

On Monday, I'll take a look at what one expects in a normal July in the tropics, and speculate on what will happen the next two weeks.

Have a great Sunday, everyone!
Jeff Masters

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A quiet weekend for the tropics

By: JeffMasters, 2:42 PM GMT on July 08, 2006

The tropical Atlantic has gone very quiet this weekend, and I can't see any disturbances worth discussing, not even in the model forecasts for the coming week. In particular, wind shear is expected to remain quite high through at least Tuesday over the Gulf of Mexico--the place we most commonly get July tropical storms.

New Katrina book
There are several books out on Katrina now, and I am reading one I highly recommend to anyone interested in the disaster:

The Storm: What went wrong and why during Hurricane Katrina--the inside story from one Louisiana scientist.

The author, Dr. Ivor van Heerden, is cofounder and deputy directory of the Louisiana State University Hurricane Center and director of the Center for the Study of Public Health Impacts of Hurricanes. He holds a Ph.D. in marine sciences from LSU, and serves as associate professor of civil and
environmental engineering there. Van Heerden had a very unique perspective of Katrina. He worked tirelessly in the decade leading up to the storm to improve our scientific understanding of how Louisiana's wetlands protect New Orleans from hurricanes. He also worked extensively with FEMA, the Army Corps of Engineers, and political figures at the local, state, and U.S. Congressional levels to try to improve New Orleans' disaster readiness. In the aftermath of the storm, he provided support for the search and rescue efforts and plugging of the levee breaches, then headed one of the teams assigned to figure out what caused the levees to fail.

The New York Times has a review of the book for those interested, and I'll be posting my own review sometime during the coming week.

Enjoy another quiet weekend in the tropics, everyone!

Jeff Masters

Updated: 2:43 PM GMT on July 08, 2006

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A quiet day in the tropics

By: JeffMasters, 1:18 PM GMT on July 07, 2006

An area of disturbed weather in the western Caribbean is expected to move onshore the Yucatan Peninsula tonight with no development. We'll have to watch this disturbance when it crosses into the southern Gulf of Mexico Saturday. The computer models are not predicting development, though.

The area of disturbed weather south of the Carolinas is associated with a front, and no tropical development is expected. The computer models continue to show an area of low pressure developing in the vicinity of this front tonight. It is now apparent that this low will be extratropical, since it is expected to form where there is a strong front with contrasting temperatures on either side. The low is expected to move north and bring strong winds to the Outer Banks of North Carolina on Saturday, and possibly to Cape Cod on Sunday. Elsewhere in the tropics, there is nothing of note today.


Figure 1. Current weather map for the Southeast U.S. shows a front and plenty of rain south of the Carolinas.

Tropical, subtropical, extratropical?
It is often difficult to tell from looking at forecast model data this time of year whether a low that is expected to develop near the U.S. coast will be tropical, subtropical, or extratropical. The difference is important, since tropical systems have the potential to quickly grow into hurricanes, while extratropical or subtropical storms do not. So, here's a quick meteorology lesson on the differences. We talk about three main types of large-scale storms (also called cyclones):

Tropical cyclones. These include tropical depressions, tropical storms, and hurricanes (which are called typhoons the Western Pacific). Tropical cyclones have warm air at their core, and derive their energy from the "latent heat" released when water vapor that has evaporated from warm ocean waters condenses into liquid water. Tropical cyclones form only over waters of at least 80 F (26 C). One does not find warm fronts or cold fronts associated with a tropical cyclone. Tropical cyclones regularly become extratropical cyclones when they get close enough to the pole to get caught up in a front.

Extratropical cyclones. These include blizzards, Nor'easters, and the ordinary low pressure systems that give the continents at mid-latitudes much of their precipitation. Extratropical cyclones have cold air at their core, and derive their energy from the release of potential energy when cold and warm air masses interact. These storms always have one or more fronts connected to them, and can occur over land or ocean. In winter, extratropical cyclones over water can grow as strong as a Category 3 hurricane.

Subtropical cyclones. These storms occur over the oceans, and are a mix between a tropical cyclone and an extratropical cyclone. Subtropical cyclones get their energy from latent heat like tropical cyclones, and from potential energy of contrasting air masses, like extratropical cyclones. A subtropical cyclone typically has an exposed center of circulation, with very heavy thunderstorm activity in a band removed at least 100 miles from the center of circulation. The difference between a subtropical storm and a tropical storm is not that important as far as the winds they can generate. It is common for an extratropical cyclone to form over cold waters, move Equatorward over warmer waters, and gradually acquire a warm core and enough deep thunderstorm activity to be classified as a subtropical storm. Eventually, many of these will become full-fledged tropical storms if the deep thunderstorm activity can move all the way to the center, and the core becomes warm from the surface to the upper atmosphere. Subtropical cyclones very rarely attain hurricane strength.


I'll be back tomorrow with an update on the tropics. On Monday I plan to discuss the long range outlook for July, and when we might start to see some action in the Atlantic. I really don't see much to be concerned about in the next few days, and the long range outlook--so far--is for typical July weather. This is not the Hurricane Season of 2005!

Jeff Masters

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A few areas of disturbed weather

By: JeffMasters, 7:14 PM GMT on July 06, 2006

The area of disturbed weather over South Florida has weakened and is no longer a threat. An associated area of disturbed weather is building off the East Coast of Florida, and has some potential for development over the next two days as it heads north towards the Carolinas. Computer models continue to show development of a weak tropical or subtropical system Friday night or Saturday south of the Carolinas. This system would then get swept up the coast this weekend, possibly bringing strong winds to Cape Hatteras. The storm would continue moving up the coast, passing several hundred miles east of Cape Cod on Sunday night. The chances of this system becoming a hurricane are very low.


Figure 1. Current satellite image of the Gulf of Mexico and Florida waters.

We will need to watch a developing area of heavy thunderstorm activity over the northern Gulf of Mexico near Mississippi the next few days, since wind shear is light and the ocean waters are warm. None of the computer models forecast development from this area, however. The rest of the tropical Atlantic is quiet today. A large area of African dust covers the entire Atlantic between Africa and the eastern Caribbean, and will act to suppress tropical storm formation in those regions over the next few days.

Jeff Masters

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South Florida disturbance; African dust

By: JeffMasters, 1:39 PM GMT on July 06, 2006

An area of disturbed weather over South Florida, the Bahama Islands, and Cuba is associated with a broad trough of surface low pressure and an upper-level low pressure system. Wind shear is down to 5-15 knots, which is marginally favorable for development. Water temperatures are very favorable, 28 - 29 C. The center of the upper low has drifted to a position at the extreme southwestern corner of Florida. There are a few impressive thunderstorms kicking up near the center of circulation, but this activity is of pretty limited coverage, and development into a tropical depression is unlikely today. Winds at the surface do show a U-shaped pattern (a trough) curving around an axis of low pressure in the region, but there is no closed circulation at the surface. There is only a closed circulation in the upper atmosphere.

Development is being hindered by the system's close proximity to land, and it will do better if it can move away from the coast. The NOGAPS model is suggesting that the low may move more into the Gulf of Mexico and show some slow development, but the rest of the models disagree. They indicate that the current low will not develop at all, but that a new low associated with the same surface trough of low pressure will develop on Saturday south of the Carolinas. This system would then get swept up the coast this weekend, possibly bringing strong winds to Cape Hatteras. The storm would continue moving up the coast, passing several hundred miles east of Cape Cod on Sunday night.


Figure 1. Current satellite image of the blob of disturbed weather over South Florida.

The rest of the tropical Atlantic is quiet today. A large area of African dust covers the entire Atlantic between Africa and the eastern Caribbean, and will act to suppress tropical storm formation in those regions over the next few days.

Jeff Masters

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Bahamas Blob update

By: JeffMasters, 8:17 PM GMT on July 05, 2006

An area of disturbed weather over the Bahama Islands is associated with an upper-level low pressure system. This low is kicking up some strong thunderstorms over the Bahamas and Cuba, but has not improved in organization today. The low is cold-cored, and is making the slow transition to a warm-cored system. It needs to have a warm core in order to develop into a tropical storm. It typically takes three or more days sitting over warm water for this process to happen (let's call today day two of its existence). Wind shear is down to 5-20 knots as of 2pm EDT, which is marginally favorable for development. Water temperatures are very favorable, 28 - 29 C. However, there is little thunderstorm activity near the center of circulation, which is southeast of Key Largo, FL. All the thunderstorm activity is well away from the center, making it unlikely that we'll see a tropical depression today or tomorrow. One of the key signs that a cold-cored system is making the transition to warm-cored is that one has substantial thunderstorm activity near the center of circulation.

The big question is if the center of circulation will be over water or land Thursday and Friday. Right now, it appears that the center is moving north-northwest, and will be over the Florida Peninsula Thursday. Most of the models indicate that the center will continue moving north-northwest, and stay over the Florida Peninsula most of Thursday and Friday. Should the center emerge into the Gulf of Mexico, or remain off the East Coast of Florida, we could see a tropical or subtropical depression by Friday. The low is expected to get picked up by a strong trough of low pressure emerging off the East Coast Friday, then get swept up the coast this weekend. Both the GFS and UKMET models predict that the low will from into a tropical or subtropical depression south of North Carolina by Saturday, and bring tropical storm-force winds to the North Carolina Outer Banks on Saturday and Massachusetts' Cape Cod on Sunday. If you have plans to be either place this weekend, keep a watchful eye on the tropics! This situtation is very similar to what we had at the end of June, when we almost had Tropical Storm Beryl hitting eastern North Carolina.


Figure 1. Current satellite image of the blob of disturbed weather over the Bahamas.

The rest of the tropical Atlantic is quiet today.

Jeff Masters

Updated: 8:24 PM GMT on July 05, 2006

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Another Bahamas Blob to watch

By: JeffMasters, 1:48 PM GMT on July 05, 2006

An area of disturbed weather over the Bahama Islands is associated with an upper-level low pressure system. This low is kicking up some strong thunderstorms just east of Florida, and is expected to drift west over Florida by Thursday. The low is cold-cored, but is making the slow transition to a warm-cored system. It needs to have a warm core in order to develop into a tropical storm, and this process typically takes three or more days. Wind shear in the area is marginaly favorable for tropical cyclone formation today, 10 - 20 knots. This shear is forecast to decrease over the next day. There is an area of dry air over Florida for the system to contend with, and development will be hindered if its circulation center moves over the Florida Peninsula as expected Thursday. However, by Friday or Saturday, several computer models are indicating the possibility that the center will move back over the water east of Florida or Georgia, and a tropical cyclone will develop. Any storm that does develop is likely to get whisked quickly northwards or northeastwards by a strong trough of low pressure expected to move off the East Coast this weekend. People planning on spending the weekend on the Outer Banks of North Carolina should keep a careful eye on this system--the situtation is very similar to what we had at the end of June, when we almost had Tropical Storm Beryl hitting eastern North Carolina.


Figure 1. Current satellite image of the blob of disturbed weather over the Bahamas.

The rest of the tropical Atlantic is quiet today.

Jeff Masters

Updated: 8:16 PM GMT on July 05, 2006

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No fireworks in the tropics today

By: JeffMasters, 3:09 PM GMT on July 04, 2006

There will be no natural fireworks in the tropics today--unless you happen to be in the Western Pacific, where Category 4 Typhoon Ewiniar is chugging north over the open ocean. "Ewiniar" is the Chuuk Islands' (Micronesia) traditional storm God, and his namesake storm is thankfully expected to weaken to Category 1 strength before threatening Japan this weekend.

In the Atlantic, there is an area of disturbed weather over the Bahama Islands associated with an upper-level low pressure system. This low is kicking up some strong thunderstorms just east of Florida, and is expected to drift west-southwest over Florida by Wednesday. Tropical development of this area is unlikely today and tomorrow. There will be strong northwestery flow of air at upper levels over Florida that should bring unfavorable wind shear to the system, and there is also a large area of dry air to contend with. However, by Friday or Saturday, computer models are indicating the possibility that something could develop east of Florida or south of Cape Hatteras, North Carolina, and zip northwards along the East Coast. This development could be non-tropical, though.

The other area we need to watch the next few days is the Gulf of Mexico. While there is currently no activity of note, wind shear will be light enough in some regions of the Gulf to allow slow tropical development over the next few days. The rest of the tropical Atlantic is quiet today.

Have a great 4th of July, everyone!
Jeff Masters

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Judge restricts NOAA hurricane hunter jet

By: JeffMasters, 2:48 PM GMT on July 03, 2006

There is little worth mentioning in the tropics today. The tropical disturbance in the Gulf of Mexico has moved ashore into Texas. A strong tropical wave is approaching the Lesser Antilles Islands, but is under 30 knots of westerly wind shear that will prohibit development. A large area of cloudiness off the east coast of Florida is also under high wind shear. Tropical storm development in the Atlantic is unlikely for at least the next two days.

Judge restricts NOAA hurricane hunter jet
A federal labor judge ruled Friday that the high-altitude NOAA Gulfstream jet cannot fly into the core region of hurricanes any more. The judge ruled in favor of the NOAA's labor union, which argued that flying the jet into the core of a hurricane, even at high altitude where turbulence is generally light, posed an unacceptable risk to the crew.


Figure 1.The NOAA Aircraft Operations Center's Gulfstream IV jet, nicknamed "Gonzo" after the Muppets character, operates out of MacDill Air Force Base in Tampa, Florida. Image credit: NOAA.

The NOAA jet generally files at altitudes of 43,000 feet around the periphery of hurricanes, dropping dozens of dropsonde probes that fall on parachutes through the storm that radio back information on temperature, winds, pressure, and humidity. These measurements have been shown to improve track forecasts of hurricanes by as much as 25%, and are crucial to the Hurricane Center's operational forecasts. Generally, the NOAA jet avoids the central core area of a hurricane, where the potential for dangerous turbulence is highest. However, in 2003 the NOAA jet flew into the eye of Hurricane Fabian near Bermuda, by entering through a large gap in the eyewall. Flights into the core regions of Tropical Storm Emily and Franklin in 2005 were also performed, although in all these cases the aircraft was careful to avoid penetrating thunderstorms, and just flew through the high cirrus clouds of the Central Dense Overcast (CDO). Nevertheless, the union argued that such flights were too dangerous, and collected little valuable data.

The Gulf Stream IV jet is a much different king of aircraft than the low-altitude P-3 and C-130 hurricane hunter aircraft, which can shrug off the moderate turbulence one typically finds in hurricane clouds. Moderate turbulence poses a much higher risk to the Gulfstream IV jet, because is flies so much faster. Flying through CDO in the core region of a hurricane presents an increased risk of moderate turbulence, due to the presence of strong wave-like features that propagate through this region. I question whether this increased risk is worthy of causing a ban on all flights into the core region of a hurricane, because in nearly all cases this can be safely accomplished if the crew and pilot exercise good judgment. However, as a member of a crew that once exercised bad judgment in deciding to penetrate Hurricane Hugo's eyewall, I can certainly sympathize with the union's case.

While the new ruling will not significantly affect the Gulfstream IV jet's current ability to provide improved data in support of better hurricane forecasts, it may substantially affect its future role. An airborne Doppler radar system was due to be installed on the NOAA jet by 2009. Data from this radar would be of most value if the jet could fly into the inner core region of hurricanes. With the jet now restricted from going to where the radar data would be of most value, the plans for the new radar may have to be scrapped. This is not necessarily a bad thing, since the heavy new radar would substantially reduce the the flight altitude of the jet. This would significantly decrease the value of the dropsonde data, since the probes would not be able to sample the upper reaches of the storm any more. In the end, the union's victory may turn out to be a positive for all concerned.

Jeff Masters

Updated: 2:50 PM GMT on July 03, 2006

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South Texas disturbance; Shuttle launch weather

By: JeffMasters, 2:39 PM GMT on July 02, 2006

An area of disturbed weather continues in the western Gulf of Mexico, near the Texas/Mexico border. The thunderstorm activity has become better organized this morning, and wind shear has dropped to 10 knots over the region. There are no signs of a surface circulation or the development of upper level outflow, but the disturbance has a good-sized area of heavy thunderstorm activity. Wind shear is forecast to remain below 15 knots through Monday night, which may allow for some continued development. However, the disturbance is very close to land, and will likely move ashore before developing into a tropical depression. South Texas/Northeast Mexico should get a good soaking on Monday, bringing the threat of flash flooding. So far, the rains have been welcome, as the region is under extreme drought.


Figure 1. Long range radar out of Brownsville showing the tropical disturbance of the Gulf of Mexico.

Space Shuttle launch weather
The weather for today's 3:26 pm EDT launch of the Space Shuttle looks bad, as thunderstorms more numerous than yesterday's are starting to pop up across the Florida Peninsula. Yesterday, the Shuttle got very unlucky--there were only two major thunderstorms in central Florida at launch time, and one of them happened to be within 20 miles of the Shuttle.


Figure 2. Satellite photo of Florida weather at launch time Saturday shows the unlucky thunderstorm that forced Discovery to scrub.

Jeff Masters

Updated: 2:47 PM GMT on July 02, 2006

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Quiet tropics; Space Shuttle launch weather

By: JeffMasters, 1:33 PM GMT on July 01, 2006

An area of disturbed weather continues in the southwestern Gulf of Mexico, southeast of Texas. The thunderstorm activity has little organization, and strong upper-level winds from the west are creating 20-30 knots of wind shear over the system. High wind shear will continue over the Gulf the next few days, making it very unlikely for this this system to develop. The disturbance will move slowly northwest and being welcome heavy rains to South Texas and Northeast Mexico. Extreme drought conditions prevail there.


Figure 1. Total precipitation over South Texas from the Gulf of Mexico tropical wave.

Elsewhere in the tropics, there is nothing of note happening.

Space Shuttle launch weather
The weather for today's 3:49 pm EDT launch of the Space Shuttle will probably be OK at the launch site, since an easterly sea breeze is expected to push today's thunderstorm activity inland. However, upper level westerly winds may carry the upper "anvil" portion of any thunderstorms that might develop west of the launch site back east over the Shuttle, creating high clouds that the shuttle cannot fly through. I give the Shuttle a 60% chance of good enough weather to fly today. Go, Discovery!

Jeff Masters

Updated: 1:33 PM GMT on July 01, 2006

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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.