Lesser Antilles may see a tropical storm late this week
A concentrated area of intense thunderstorms near 9N 36W, midway between Africa and the Lesser Antilles Islands, has become more organized this morning. NHC has labeled this system Invest 91L, and is giving it a 60% chance of developing into a tropical depression by 8am Tuesday. Wind shear is a moderate 10 - 20 knots, sea surface temperatures are at record highs, and the dust and dry air of the Saharan Air Layer (SAL) are far enough to the north of 91L to potentially allow further development. The main negatives for development are the current phase of the Madden-Julian Oscillation, which favors downward motion over the tropical Atlantic, and the fact that 91L is too close to the Equator to take much advantage of the Earth's spin to get spinning. Last night's ASCAT pass of the region did show a large region of westerly winds south of 91L, indicating that a surface circulation is trying to form. Satellite imagery shows that the intensity and areal extent of 91L's heavy thunderstorms is increasing. However, there are no signs of a surface circulation, and low-level spiral bands and upper-level outflow are not apparent yet.
Forecast for 91L
There is strong model support for 91L developing into a tropical depression. The GFS, ECMWF, NOGAPS, and UKMET models all develop 91L into a tropical depression by Tuesday or Wednesday. A west to west-northwest motion is predicted, and residents of the Lesser Antilles Islands should anticipate the possibility of a tropical storm arriving in the islands as early as Thursday. It is possible that 91L would pass northeast of the islands, as predicted by the UKMET model, and it is too early to speculate on which of the islands is at most risk. As the storm approaches the Lesser Antilles late this week, 91L will encounter a strong upper-level low pressure system centered north of Puerto Rico. This upper-level low will likely bring high levels of wind shear to the waters just north of Puerto Rico and Hispaniola. Thus, if 91L stays to the south, in the Caribbean, it is far more likely to attain hurricane status than if it pushes north of the Caribbean. As always, long range forecasts of this sort are speculative, and it is too early to reliably say what the long-term risks of 91L becoming a hurricane are. The latest intensity forecast from the SHIPS model shows 91L peaking in strength four days from now, then weakening as it encounters the high wind shear area north of Puerto Rico.
Figure 1. Morning satellite image of Invest 91L.
Next update
I'll have an update Monday morning.
Jeff Masters
Reader Comments
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Really!
....
Further NORTH of Georgia should monitor this system. I think it's all clear from the GOMEX, IMHO.
Tropical Tidbit for Sunday, August 1st, with Video
Back later.
Dont say the dreaded F word on here...The wishcasters hate fish storms. With that being said I do agree that that is a fish storm or headed to Bermuda possibly. That was my thinking all along and the models are starting to verify that!
Its a little early to write off anything..no?
The ascat confirmed the location of max vorticity.
Let the fighting begin. And many wonder why I only observe here anymore.. This thing is over a week away from the US and already the bickering begins on landfall.
It is STILL fighting the ITCZ. Take a pill. Enough of the "it's gonna hit here, cause I want it to hit here to feel important" forecasts. Pay attention to those folks here who know what they are doing...
Weatherguy03
StormW
Levi
Drakoen
Weather456
I would include myself in the list, but I really have no interest in posting obs here much anymore because of all of the infantile nonsense.
When and if things get sticky, I'll do that on my own blog.
Quoting FLdewey:
I think it's going somewhere west of where it is now for certain.
Not sure what quote is funnier.
If a system gets 35 to 38 points, a TCFA may be issued depending on Dvorak trends, and if a system gets 39 points or more a TCFA should be issued.
Surface
Condition Points
A circulation is evident using visible satellite, shortwave infrared, microwave imagery or QuikSCAT/Windsat ambiguities 3 points A circulation has been evident for at least 24 hours 5 points
A westerly surface- or gradient-level wind of 5 kt that is within 200 nm (370 km, 230 mi) south of the centre of the disturbance 5 points
Any wind associated with the system is at least 20 kt 2 points
Any wind associated with the system is at least 25 kt 3 points
Any wind associated with the system is at least 30 kt 4 points
A weather station within 200 nm of the system has reported had a pressure drop of 2 mb over 24 hours 3 points
A weather station within 200 nm of the system has had a pressure drop of 3 mb over 24 hours 4 points
The estimated MSLP of the system is less than 1010 to 1009 mb 3 points
The estimated MSLP of the system is 1008 mb or less 4 points
500 mb height
Condition Points
There is evidence of at least an inverted trough 2 points
There is evidence of a closed circulation in the system 4 points
200 mb height
Condition Points
Westerly flow of at least 15 kt over the disturbance -4 points
There is evidence of anticyclonic outflow over the centre of the disturbance 4 points
Easterly flow of at most 20 kt over the disturbance 3 points
Sea surface temperature
Condition Points
The sea surface temperature is 26 Celsius (78.8 Fahrenheit) or higher 3 points
Satellite data
Condition Points
The system has persisted for at least 24 hours 3 points
The system has persisted for at least 48 hours 4 points
The system has persisted for at least 72 hours 5 points
The system has a Dvorak classification of T1.0 to T1.5 from all three agencies (TAFB, SAB, AFWA) 3 points
The system has a Dvorak classification of T1.5 to T2.0 from all three agencies 5 points
The Dvorak final-T number has decreased by T0.5 to T1.0 from two or more agencies -2 points
Miscellaneous
Condition Points
The cloud system is north (or south) of 5 degrees latitude 3 points
The tropical system is within 72 hours of reaching a Department of Defense resource 3 points
The cloud system center and the satellite centre fixes for the system are within 2 degrees of each other 2 points
**********************************************************
I think that the NHC is waiting to 8 pm in order to upgrade anything.
Karma. Cirro posted this right after you.
It seems to show an S shape like you mention. Can that be attributed to the upper level anticyclone? Something has to be making the S shape appear in multiple cases of development and the upper level anticyclone seems to be a likely cause.
The convection to the east seems to be gaining on the upper level circulation. I'll go with it and use the ascat for surface traction. That's assuming something develops. If the anticyclone pulls up convection outside the area of the pouch, then dry air may well get drawn in which will quash the whole deal.
Come up north here. 79 degrees currently.
1552. CaneBeast2010
This comment has been removed for violating the Community Standards.
why dont they just ban him again
works for me
My point made again... How can anyone possibly say with any scientific certainty "it was my thinking all along" when we don't even have a developed system to track yet?
C'mon.
I got 40
My temperature gauge in my Ford Focus showed 105 degrees outside.
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