Caribbean disturbance 93L growing more organized

An area of disturbed weather (93L) a few hundred miles east of the Nicaraguan coast, is growing more organized, and has the potential to develop into a tropical storm this week. This morning's QuikSCAT pass revealed that the circulation center near 12N 81W is better defined and is more circular. However, visible satellite images show that the heaviest thunderstorm activity is about 200 miles to the north of the center, and there is very little heavy thunderstorm activity near the center. It appears that the center of circulation is now attempting to relocate near the heaviest thunderstorms, somewhere near 14N 81W. This relocation will make last night's model runs a poor judge of how 93L might develop. The disturbance has been drifting west-northwest to northwest over the past 18 hours. Wind shear is a moderate 15 knots, and heavy thunderstorm activity has shown a moderate increase in intensity and areal coverage over the past few hours.


Figure 1. Current satellite image of 93L.

The forecast
Wind shear is expected to remain in the moderate range, 10-20 knots, over the southern Caribbean during the next three days. Water temperatures are warm, 29.5°C, and this warm water extends to great depth. These are favorable conditions for intensification, and both the GFDL and HWRF models predict 93L will become a hurricane, with the HWRF predicting a major hurricane. However, the SHIPS intensity model predicts only a weak tropical storm with 40 mph winds. I give 93L a 40% chance of eventually becoming a hurricane.

Steering currents are weak, but a slow northwest motion to a point just offshore the Nicaragua-Honduras border is likely through Thursday. At that time, a strong trough of low pressure will be approaching the U.S. East Coast. The models are split on whether this trough will be strong enough to pull 93L northward. The GFDL, HWRF, and ECMWF models predict the trough will turn 93L northward then northeastward, bringing the storm near the Cayman Islands by Saturday and Jamaica by Sunday. The UKMET, GFS, and NOGAPS models disagree, bringing 93L ashore over northern Nicaragua by Friday, and keeping the storm trapped near the north coast of Honduras through Monday. Given the probable center re-formation 200 miles to the north currently underway, the more northerly threat to the Cayman Islands and Jamaica appears to be the more likely scenario.

Given the current increasing trend in organization, I believe 93L will become a tropical depression on Wednesday and Tropical Storm Paloma by Thursday. NHC is giving 93L a medium (20%-50% chance) of developing into a tropical depression by Thursday morning.

Northeastern Nicaragua and northeastern Honduras are at risk of heavy rains from 93L beginning Wednesday. Total rainfall amounts of 4-8 inches are likely through Thursday in the region. These heavy rains may spread westward to the Belize border by Friday, if the storm resists being pulled northward by the trough. Panama and Costa Rica should receive only another 1-2 inches. Heavy rains will likely move into the Cayman Islands and Jamaica on Wednesday or Thursday, and may affect Cuba by Friday and Haiti by Saturday. Currently, no models are showing a threat to Florida or the Bahamas from 93L, but that could change with the next set of model runs, after the center re-formation is taken into account. The first Hurricane Hunter flight into 93L is scheduled for Wednesday afternoon.

Links to follow
Wundermap for 16N 84W

I'll have an update Wednesday morning, or later today if there's a major change to report. It's time to go vote!

Jeff Masters