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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ok
Yes and no. They are debatable. Later research suggested it was exaggerated.
There have of course been winds higher than that - Olivia off the north coast of Australia - but that was a gust, not sustained.
Of course, 'official' is the key word. Winds have probably been higher in both cases, just haven't been measured and calibrated.
UKMET still showing the recurve.
I've never known the Navy to work on weekends. I've never known the Air Force to work past 4 o'clock.
NEAR 10 KT. THE WAVE IS EMBEDDED WITHIN AN AREA OF HIGH TOTAL
PRECIPITABLE WATER FROM 05N TO 18N BETWEEN 26W AND 39W. NEAR THE
SOUTHERN EXTENT OF THE WAVE AXIS...A 1008 MB LOW IS CENTERED
NEAR 09N35W AND IS PROVIDING FOCUS FOR SLOW ORGANIZATION OF
ONGOING CONVECTION. A SMALL EAST TO WEST RIBBON OF LOW DEEP
LAYER WIND SHEAR VALUES AND A FAVORABLE UPPER LEVEL DIFFLUENT
ENVIRONMENT ENCOMPASS THE SYSTEM FROM 08N TO 12N BETWEEN 30W TO
40W. THIS WILL RESULT IN FURTHER ORGANIZATION OF THE SYSTEM AND
ASSOCIATED CONVECTION OVER THE NEXT COUPLE OF DAYS. SCATTERED
MODERATE AND ISOLATED STRONG CONVECTION IS FROM 08N TO 13N
BETWEEN 30W AND 39W.
Never gets to 66W. I have a feeling the ECMWF is going to trend east and north.
A tropical depression has to have a closed, well-defined circulation with organized deep convection around the center. 91L is a designation for an area of investigation by the NHC, and has nothing to do with the potential for development of the system. It also has no criteria required for declaring an invest so the fact that something is an invest means absolutely nothing except that the NHC is interested in it.
CHGQLM
ATTENTION...NATIONAL HURRICANE CENTER
NCEP COUPLED GFDL HURRICANE MODEL FORECAST MADE FOR
TROPICAL DEPRESSION INVEST 91L
INITIAL TIME 12Z AUG 1
DISCLAIMER ... THIS INFORMATION IS PROVIDED AS GUIDANCE. IT
REQUIRES INTERPRETATION BY HURRICANE SPECIALISTS AND SHOULD
NOT BE CONSIDERED AS A FINAL PRODUCT. PLEASE SEE THE TPC/NHC
OFFICIAL FORECAST.
FORECAST STORM POSITION
HOUR LATITUDE LONGITUDE HEADING/SPEED(KT)
0 10.2 36.2 290./ 8.9
6 10.4 36.9 286./ 7.1
12 10.4 37.5 278./ 6.1
18 10.7 38.1 292./ 6.0
24 11.5 39.1 311./12.7
30 12.4 40.7 298./18.3
36 12.9 42.5 286./18.3
42 13.5 44.3 289./18.3
48 14.4 46.3 294./21.7
54 15.3 48.5 290./22.8
60 15.9 50.8 287./22.6
66 16.6 52.7 289./19.5
72 17.2 54.3 290./16.4
78 18.1 56.2 296./20.0
84 18.9 58.0 295./19.1
90 19.8 59.3 302./15.1
96 20.9 60.2 321./13.7
102 22.1 61.5 314./17.2
108 23.4 62.8 315./18.0
114 24.2 64.3 300./15.9
120 25.0 65.3 304./11.7
126 25.7 66.3 306./11.7
Thank you :)
when dos the site update next
well we have the points we need
so the word invest is short for investigation???
Similar to the UKMET.
Which includes South Florida.
I got 42.
or me
I agree, it's doubtful that there were 215 mph sustained winds in the system. But it's down in the record books and officially recorded. Hasn't been revised down like Mitch yet.
http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=1174
Hurricane Gustav, which pounded Cuba as a Category 4 hurricane in August. Gustav set a new world record for highest wind gust ever measured in a hurricane...
Not only is this the highest wind speed ever measured in a hurricane, it is the second highest wind gust ever measured at a non-mountain location on Earth, and is the third highest wind gust ever measured on the surface of the planet.
Note: this post was updated in 2010 to reflect the official WMO review of Gustav's wind gust,
Maybe it'll trend back here shortly.
someone could see a monster
when does this model update tia
Link
Correct.
TCFA- Tropical cyclone formation alert!!
Gustav was probably a Category 5 at Cuba landfall. Doppler Radar in 1999 clocked the Oklahoma tornado at 312 mph or something, you could almost consider that a F6.
I believe that forecast is from the humans at UKMET using their model, so they would be similar.
ECMWF and UKMET are very different creatures.
and we could have a TD later today or tonight
Oh I don't think they start sending those until the system gets to 50W or 55W, forget which.
I recall learning earlier in the year that they didn't issue those on weekends. I could be wrong though.
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