TD 8 forms; 97L a potential threat to the Caribbean and U.S.

By: Dr. Jeff Masters , 3:30 PM GMT on August 19, 2011

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Tropical Depression Eight formed last night near the coast of Honduras, and is headed westwards towards a landfall in Belize on Saturday. TD 8 is a small storm, so will impact a relatively small area of northern Honduras, northern Guatemala, all of Belize, and southern portions of Mexico's Yucatan Peninsula. TD 8 has just enough room between its center and the coast of Honduras to intensify into a moderate strength tropical storm with 50 - 60 mph winds before landfall. It is very unlikely TD8 has the time or room to intensify into a hurricane; NHC gave the storm just a 7% chance of making it to hurricane strength in their 11am EDT wind probability forecast. Should TD8 make it to tropical storm strength, it would be called Harvey.


Figure 1. Morning satellite image of TD 8.

Invest 97L likely to become a tropical storm next week, could threaten the U.S.
A tropical wave near 14°N 48°W, about 800 miles east of the Lesser Antilles Islands, is moving westward near 20 mph. This wave, designated Invest 97L by NHC yesterday, has seen a marked increase in its heavy thunderstorm activity this morning, but dry air to the north and west is slowing development. An impressive amount of large-scale spin is obvious in visible satellite loops, but the storm is at least a day away from forming a well-defined surface circulation. Ocean temperatures are about 28.5°C, about 2°C above the threshold needed to support a tropical storm, and wind shear is low, 5 - 10 knots.


Figure 2. Morning satellite image of the tropical wave 97L.

The computer models have shown an unusual amount of agreement in developing 97L over the past few days, and all the ingredients seem to be in place for a tropical storm to form by Monday or Tuesday as 97L crosses the Northeast Caribbean. The atmosphere is expected to be moister over the Caribbean, wind shear will remain a low 5 - 10 knots, and sea surface temperatures will increase to near 29°C. The main impediment for development will likely be two-fold: too much dry, stable air, and proximity to land.

As seen in Figure 3, there has been an unusual amount of dry, stable air in the Atlantic this year, due to a combination of dry air from Africa, and upper-atmosphere dynamics creating large areas of sinking air that dry as they warm and approach the surface. This stable air has been largely responsible for the fact that none of our seven tropical storms so far this year has made it to hurricane strength, despite the presence of sea surface temperatures that are the 3rd warmest on record across the tropical Atlantic. Tropical Storm Emily in early August encountered problems with dry air when it crossed the Northeast Caribbean, and 97L may have similar difficulties.


Figure 3. Vertical instability of the atmosphere during 2011 in the Caribbean (left) and tropical Atlantic between the Lesser Antilles Islands and coast of Africa (right.) The instability is plotted in °C, as a difference in temperature from near the surface to the upper atmosphere. Thunderstorms grow much more readily when vertical instability is high. Observed vertical instability (blue line) has been much lower than the climatological average from previous years (black line), due to an unusual amount of dry air in the atmosphere, inhibiting tropical storm development this year. Image credit: NOAA/CIRA.

Encounters with land will be another potential major problem for 97L. Most of the computer models take 97L near or over Puerto Rico Sunday night, then very close to or over mountainous Hispaniola Monday night through Tuesday. It is unlikely that 97L will be stronger than a 55 mph tropical storm when it encounters these islands, and passage over the islands could severely disrupt the storm. However, if 97L takes a path just south or north of Hispaniola, the potential exists for the storm to intensify into a hurricane.

There will be moderate wind shear of 10 - 20 knots to the north of the islands early next week, so a path just to the south of the Dominican Republic and Haiti would be more likely to let 97L intensify into a hurricane. A west-northwest motion is likely for 97L through Wednesday, which would bring the storm to the vicinity of Jamaica-Central Cuba-the Central Bahamas on Wednesday. On Wednesday and Thursday, the models agree that a trough of low pressure will dip down over the Eastern U.S., which is likely to turn 97L to the north. The exact timing and strength of this trough varies considerably from model to model, and will be critical in determining where and when 97L will turn to the north. The best model for predicting the timing and strength of such troughs over the past two years has been the ECMWF (European Center model), and this model currently brings 97L into the Florida Keys on Thursday night next week. You can view ECMWF forecasts on our wundermap with the model layer turned on. The European Center does not permit public display of tropical storm positions from their hurricane tracking module of their model, so we are unable to put ECMWF forecasts on our computer model forecast page that plots positions from the other major models.

Remember that a 7-day forecast by even our best model will be off by an average of over 700 miles, so it is too early to tell what part of the U.S. might be most at risk from a strike by 97L. This weekend would be a good time to go over your hurricane preparedness.


Figure 4. Morning satellite image of Invest 98L off the coast of Africa.

Invest 98L near the coast of Africa
A tropical wave near the coast of Africa, a few hundred miles southeast of the Cape Verde Islands, is moving west to west-northwestward at 10 - 15 mph. This wave, designated Invest 98L by NHC yesterday, is large and well-organized, with a modest amount of spin and heavy thunderstorm activity. 98L will bring strong, gusty winds and heavy rains to the Cape Verde Islands today and Saturday as the storm skirts to the south. So far this morning, top sustained winds measured in the islands were 24 mph at Mindelo. Water temperatures are warm, near 27 - 28°C, and wind shear is low, 5 - 10 knots, so 98L should continue to organize today. NHC gave the storm a 50% chance of developing into a tropical depression in their 8am advisory. Once 98L passes to the west of the Cape Verde Islands, it has a long stretch of ocean to cross before it could affect any other land areas. Approximately 70 - 80% of all tropical cyclones that pass this close to the Cape Verde Islands end up curving out to sea and not affecting any other land areas, according to Dr. Bob Hart's excellent historical probability of landfall charts. The latest set of long-range model runs go along with this idea, but it is too early to be confident of this.

Jeff Masters

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1542. Gearsts
Quoting Skyepony:
Today's Oceansat pass of 97L
Is that 97L seem like a error on the map. To far south
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Quoting Tazmanian:
99L looks good at this time and if it keeps moveing a little S i dont see this a fish storm all so re call ike at 1st mode run was forcast too turn in too a fish and head out too sea but has it stayed weak it headed more and more W and so did the mode runs with it


same deal for 98L
I see 99L staying south as well Taz.
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I'm going with southern track with 97L, everything has been going west this year and see no reason why this wouldn't either. GOM bound
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The spin you are seeing is not in the low levels, it's a mid level spin that should be able to work its way down to the surface. Which is why I believe we will see a 60% chance at 8 p.m. Remember, if it develops a bit quicker, you can basically throw away the southern solution. I'm still leaning towards the East Coast of Florida on this one.
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new two


from me



97L get a high 60 too 80% i may be a little high on that

98L gets a high 60% may be 70%


99L may get a 30-60% ch at the next two
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It's very obvious where 97L wants to gel but, wanting and getting are two different things.
Member Since: August 19, 2005 Posts: 5 Comments: 4863
Quoting PensacolaDoug:
97L looks to be a TD on sat pics now if not already a TS.


It does have an impressive satellite appearance, but it is lacking a low-level circulation, like 93L was for two days or so.
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99L looks good at this time and if it keeps moveing a little S i dont see this a fish storm all so re call ike at 1st mode run was forcast too turn in too a fish and head out too sea but has it stayed weak it headed more and more W and so did the mode runs with it


same deal for 98L
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Time: 21:47:30Z
Coordinates: 22.6833N 86.6167W
Acft. Static Air Press: 392.0 mb (~ 11.58 inHg)
Acft. Geopotential Hgt: 7,725 meters (~ 25,344 feet)
Extrap. Sfc. Press: -
D-value: 399 meters (~ 1,309 feet)
Flt. Lvl. Wind (30s): From 271° at 2 knots (From the W at ~ 2.3 mph)
Air Temp: -16.1°C* (~ 3.0°F*)
Dew Pt: -*
Peak (10s) Flt. Lvl. Wind: 2 knots (~ 2.3 mph)
SFMR Peak (10s) Sfc. Wind: 0 knots* (~ 0 mph*)
SFMR Rain Rate: 1 mm/hr* (~ 0.04 in/hr*)
(*) Denotes suspect data

Recon more than half way to Harvey
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Quoting FLdewey:
Things are heating up... DOOM:CON™ has been updated.

The Atlantic is a brewin.

WEST!


I hope you notified FEMA.
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Quoting KEEPEROFTHEGATE:
NEARING LANDFALL


Yeah, in 24-36 hours or so.
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97L looks to be a TD on sat pics now if not already a TS.
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My man REEDZONE back in the house to talk about 97L.Does he do blogs on here?.
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1527. KEEPEROFTHEGATE (Mod)
Quoting WeatherNerdPR:
Is that an...

...eye?
NEARING LANDFALL
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Quoting WeatherNerdPR:
Is that an...


Not yet, but probably soon.
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Quoting Hoff511:
if 98L and 99L develop and do it fast 97L could potentially be Katia!


If that happened, 2011 would be right on pace with 2005 in terms of number of named storms.
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Is that an...

...eye?
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Quoting MississippiWx:
Wow...the tropics are going nuts. Of particular interest to me is Harvey. I'm starting to think hurricane for him...

heading now 280 from 275 earlier,will possibly make it as he pulls away from the coastline
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1521. Hoff511
if 98L and 99L develop and do it fast 97L could potentially be Katia!
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Might see a TD by tomorrow night, probably code red by 8 p.m. tonight. Nice mid level spin, needs to work it's way down to the low levels in order to really get going.

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1518. scott39
Quoting scott39:
Keep your eyes on the models at 80 degree W.
Now look how far N or S they are? Look for 97L to turn about there.
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99l got a floater before 98l i guess 99's the more impressive one
Member Since: July 31, 2011 Posts: 4 Comments: 753
1516. Skyepony (Mod)
Today's Oceansat pass of 97L
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The GFS has 97L near Barbados in 36 hours. Uhhh...

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Quoting ackee:
IS 97L well below the convection we are seeing now ?


Image current 45 min ago

Member Since: August 19, 2005 Posts: 5 Comments: 4863
1512. ackee
why does the GFS and CMC even the GEM have 97L centre so far south seem like THE ECMWF postion of 97L so far seem to be most on target to me
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1511. scott39
Keep your eyes on the models at 80 degree W.
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Quoting ackee:
IS 97L well below the convection we are seeing now ?


Officially yes..
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Quoting MiamiHurricanes09:
Not really. They expect some sort of organization/intensification between now and the time 97L reaches Puerto Rico, hence the more poleward track, which IMO is very plausible.


Yeah the southern track would hold if the system stays shallow, but I'm not buying that. It all depends on how fast the system develops, but I would say it clips a few islands and settles on a path just north of the chain, or it barrels through the whole island chain. Intensity is the key there, but I wouldn't expect a track too far to the south unless it stays weak.
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97L is right into diurnal minimum
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Quoting DavidHOUTX:
Anybody else think that even though the HP over Texas now will move west when 97L is getting close or if it was to enter the eastern/central gulf, the HP will still keep it clear of the Texas coast? Then again,if the storm is very strong who knows where it will go!
only one gfs run said it would hit tx odds are it wont hit tx right now anyone from mobile,al to Savannah,ga should worry about a landfall from 97l
Member Since: July 31, 2011 Posts: 4 Comments: 753
Quoting ackee:
IS 97L well below the convection we are seeing now ?



no
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1502. ackee
IS 97L well below the convection we are seeing now ?
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Good Night Folks.
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Anybody else think that even though the HP over Texas now will move west when 97L is getting close or if it was to enter the eastern/central gulf, the HP will still keep it clear of the Texas coast? Then again,if the storm is very strong who knows where it will go!
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Quoting E46Pilot:
GFS was putting 97 over south FL, earlier this week. Looks like the High will be building west. This one I think should be taken seriously no?



Just my take.

The NAO is still only weakly positive (0.99543E-01). Not too often to you get the chance to track a storm purely based on the strength of the B/A high. This is going to be one of those cases in my opinion and the NAO explicitly deals with it's strength and that of the Icelandic low . This is deep layer steering meaning that the high will guide it to the point of weakness unobstructed. I am assuming this on the fact that 97L will reach as high as the models portray. An undeveloped weak storm would obviously be subject to the status quo trade winds and move further westward. Personally, I will start to lean further westward if we see the NAO go more positive the next few days, if not, my thoughts are from west FL coast eastward.
Member Since: August 19, 2005 Posts: 5 Comments: 4863
1498. scott39
Eventual landfall track in the US depends alot on how far S that 97L is, when it gets to 80 degrees longitude.
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Quoting KEEPEROFTHEGATE:
i can assure you that will not be the case
I know I just wanted a laugh.
Quoting ecflweatherfan:


Dmin should be occurring right now (or has already passed) as the airmass over water is the most stable due to temperature differentials between the water and atmosphere is the least. The Dmax, which will occur in the pre-dawn hours when there is more instability in the atmosphere between water and airmass above the water is greatest. Therefore, we should begin to see a steady increase in convection as the evening and overnight wears on.
Thanks for explaining.
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Invest 97 worth watching by Tampa Bay residents
August is living up to its reputation as the beginning of the busiest part of hurricane season. Tropical Storm Harvey is threatening Honduras and Nicaragua, while Invests 98 and 99 are swirling off the African Coast, Tampa Bay residents need to focus for the moment on the Invest 97 which is about halfway between the Cape Verde Islands and the Lesser Antilles. According to Weather Underground founder and hurricane expert Dr. Jeff Masters "Computer models have shown an unusual amount of agreement in developing 97L over the past few days."

The spaghetti chart of computer model course projections show a definite long term trend toward courses that could threaten Florida late next week, but Masters notes that the course projections are combined with some favorable conditions for development. "All the ingredients seem to be in place for a tropical storm to form by Monday or Tuesday as 97L crosses the Northeast Caribbean. The atmosphere is expected to be moister over the Caribbean, wind shear will remain a low 5 - 10 knots, and sea surface temperatures will increase to near 29°C." On the other hand there is a lot of dry air in the region and there are any number of land masses that could weaken or destroy the storm.

Despite a healthy number of tropical cyclones and areas of interest for forecasters to watch, we still have not had a storm make it to hurricane strength so far this year. A fact that Masters chalks up to an unusually large amount of stable air that inhibits the ability of thunderstorms to grow vertically. You can see Masters' technical analysis and complete blog entry by clicking here.

According to Masters the real key to figuring out where Invest 97 goes is a low pressure trough that's expected to creep into the eastern U.S. How strong that trough is and how fast it moves will determine when 97 starts to turn north. An early turn could take up the east coast of Florida, a later turn could take it over the Florida peninsula or into the Gulf of Mexico. In any case we'll echo Dr. Masters' advice: now would be a good time make sure you are prepared.
Member Since: July 31, 2011 Posts: 4 Comments: 753
Quoting TropicalAnalystwx13:


No, the NHC is too far north.
Not really. They expect some sort of organization/intensification between now and the time 97L reaches Puerto Rico, hence the more poleward track, which IMO is very plausible.
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Quoting TropicalAnalystwx13:


No, the NHC is too far north.


They are experts ;-)
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Miami NWS Discussion

.EXTENDED FORECAST...
FOR THE MIDDLE TO END OF NEXT WEEK...THE FORECAST WILL DEPEND ON
THE STRONG TROPICAL WAVE ABOUT 800 MILE EAST OF THE LESSER
ANTILLES. AT THIS TIME...THE NATIONAL HURRICANE CENTER IS
FORECASTING THE TROPICAL WAVE TO MOVE TO THE WEST TO NORTHWEST
TOWARDS THE REGION. HOWEVER...THERE IS CONSIDERABLE UNCERTAINLY
OF THE DEVELOPMENT AND POSITION OF THE TROPICAL WAVE DURING THIS
TIME...THE FORECAST WILL REMAIN UNCHANGED WITH THE TYPICAL SUMMER
TIME WEATHER PATTERN. PEOPLE OF SOUTH FLORIDA NEED TO CONTINUE TO
MONITOR THE LATEST TROPICAL WEATHER OUTLOOKS FROM THE NATIONAL
HURRICANE CENTER ON THIS TROPICAL WAVE.
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1492. Skyepony (Mod)
Turkey~ Heavy rain that started in the early hours of Friday triggered floods in the Black Sea province of Ordu, daily Hrriyet reported on its website. Ordu Gov. Orha Dzgn said 90 kilograms of rain fell per square meter, or approximately 9 centimeters, and quoted Ordu residents as saying this was "the worst disaster that hit the city in the last 50 years." Rainfall started at around 2 a.m. Friday and continued until morning, causing the Aziziye and ahincili creeks to overflow. Floods occured on inner city roads and streets. One lane of the Black Sea Highway's portion that ran through Ordu was closed to traffic. All neighborhoods, avenues and streets in the city center were affected by the flood. Hundreds of residences and offices were left under water. There were no reports of loss of life.
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About JeffMasters

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