A very busy day in the tropics; wind shear tutorial posted

Satellite imagery and this morning's QuikSCAT pass show a vigorous surface circulation that continues to spin in the Gulf of Mexico, about 280 miles south-southeast of Brownsville, Texas. This disturbance (94L) has one clump of heavy thunderstorms on the northern side of the circulation, and QuikSCAT saw winds up to 25 mph at 8:14 am this morning. Wind shear has fallen to about 10 knots over the disturbance, and is expected to remain 10 knots or below for the next three days. This should allow 94L to develop into a tropical depression later today or on Wednesday. Steering currents are weak in the southwest Gulf of Mexico, and 94L will move slowly and erratically. This storm is primarily a threat to Mexico, due to a very strong ridge of high pressure expected to remain in place over the Gulf of Mexico the rest of the week. Several of the models foresee an eventual landfall to the west or south between Tampico and Campeche late this week. A Hurricane Hunter flight is scheduled to investigate 94L this afternoon.

Lesser Antilles disturbance 97L needs to be watched
A tropical wave (97L) was near 15N 62W, or just west of Dominica and Martinique in the Lesser Antilles Islands at 8 am EDT this morning. This wave had a closed circulation yesterday, but this circulation degenerated and was no longer fully closed on this morning's QuikSCAT pass. Top winds from QuikSCAT were about 30 mph just to the northeast of the northernmost islands in the chain. None of the islands had winds exceeding 15 mph between 8 am and 9 am EDT this morning. Satellite imagery shows heavy thunderstorm activity mostly died out last night, but is now making a comeback, with some major cells blowing up over Guadaloupe. A surface circulation also appears to be trying to form under these new cells. The wave is under about 10-20 knots of wind shear. The shear is forecast to remain near 20 knots through Thursday, which may allow some slow development. The 06Z (2 am EDT) run of the GFDL model did develop 97L into a weak tropical storm. The forecast had 97L moving over Puerto Rico on Wednesday, the Dominican Republic on Thursday, and eastern Cuba by Saturday. The 06Z HWRF model did not develop 97L. If 97L does develop, and survives passage over Hispaniola and Cuba, and survives some possible encounters with areas of high wind shear, it could arrive at the Florida coast on Sunday as a tropical storm. That's a lot of "ifs", and there is only about a 5% chance of this happening. The Hurricane Hunter mission for this afternoon into 97L was canceled, and no new missions are scheduled.

Links to follow for 97L
Martinique radar
Puerto Rico long range radar


Figure 1. Microwave image from 4:39 am EDT today showing low-level spiral banding coming together in Karen. This image is bit different from the usual 85 GHz images I show, which emphasize where it is raining through the total depth of the storm. The image above is taken at 37 GHz, where one sees more of the surface structure of the storm. Image credit: Navy/NRL.

Tropical Storm Karen forms
Tropical Storm Karen formed this morning, midway between Africa and the Lesser Antilles Islands. This large storm is still disorganized, as seen in the latest satellite loops. Low level spirals bands are slowly organizing, and with wind shear 10 knots or less, Karen should be able to steadily strengthen to a hurricane, as predicted by the SHIPS and GFDL intensity models. The HWRF model keeps Karen just below hurricane strength. Later this week, Karen may encounter a region of hostile wind shear in association with a trough of low pressure that will also turn the storm to the north or northwest. This may slow or reverse Karen's intensification.

It currently appears that Karen will not affect any land areas. It is unusual for a hurricane to turn west and hit the U.S. after going as far north as the official NHC forecast has the storm five days from now. The GFS model has consistently shown that Karen will recurve out to sea east of Bermuda next week. However, the UKMET model is showing a more southerly track just north of the Lesser Antilles islands six days from now. Should Karen follow this track, the storm may miss the trough the GFS is predicting will recurve it. In this case, Karen could be a long-range threat to Bermuda or the U.S. East Coast.

Disturbed weather over Florida and the Bahamas
An area of disturbed weather has formed over South Florida and the western Bahama Islands, in association with an upper-level trough of low pressure. The region is under about 20 knots of wind shear, which should prevent any development. This disturbance is bringing heavy rain to portions of South Florida, the Bahamas, and Cuba, as seen on long range radar out of Key West.

Hurricane Center Directorship open
The position of director of the National Hurricane Center is officially open, according to a story published today in the Miami Herald. The current acting director, veteran hurricane forecaster Ed Rappaport, will decline to apply. "The timing of this position is not right, both personally and professionally, so I have chosen not to apply," said Rappaport, 49. Leading candidates for the job include the current interim deputy director, Bill Read, and hurricane specialist Rick Knabb.

Wind shear tutorial
For those interested, I've posted a wind shear tutorial. This page is permanently linked on our tropical page.

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

Jeff Masters