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Western Caribbean disturbance 91L remaining about the same

By: Dr. Jeff Masters, 1:47 PM GMT on October 20, 2008

An area of disturbed weather associated with a large area of low pressure (91L) continues to fester off the coast of Belize in the Western Caribbean Sea. This morning's QuickSCAT pass revealed no surface circulation, although some rotation at higher levels of the atmosphere is apparent on satellite loops. The intensity and areal coverage of heavy thunderstorms in the disturbance increased some in the past few hours, spreading over the Cayman Islands. However pressures are not falling at present over the Western Caribbean. Wind shear is a high 20 knots.

The forecast for 91L
Wind shear is expected to remain in the 15-25 knot range over the next four days, which should allow some slow development of the disturbance. Steering currents are weak, and a slow movement west to a point near the Belize coast is possible today through Tuesday. Heavy rains will affect Belize, Mexico's eastern Yucatan Peninsula, and the Cayman Islands through Wednesday. A trough of low pressure swinging across the Midwest U.S. should be able to start pulling 91L northward or northwestward by Wednesday. Once 91L enters the Gulf of Mexico on Thursday, the trough should swing the storm to the northeast, bringing it across the west coast of Florida on Friday or Saturday. Wind shear will be very high over the Gulf of Mexico this week, in the 30-40 knot range, and I doubt 91L would be able to intensify into a hurricane in the face of that kind of shear. The 00Z (8 pm EDT) run of the GFDL model develops 91L into a tropical storm that hits Florida near Sarasota Friday morning with 50 mph winds. The 06Z (2am EDT) run of the GFS model is slower, predicting a landfall near Tampa on Saturday morning. However, this landfall may occur as a weaker subtropical storm or extratropical storm, as predicted by the latest phase space diagrams from Bob Hart at Florida State. The other reliable models do not develop 91L. NHC is giving 91L a medium (20-50% chance) of developing into a tropical depression by Wednesday, which is a reasonable forecast. It currently does not appear that 91L will interfere with the World Series baseball game scheduled to be played Thursday night in St. Petersburg, Florida. Batter up!

Figure 1. Latest satellite image of the Western Caribbean disturbance, 91L.

I'll have an update Tuesday morning.

Jeff Masters

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