Disturbance 93L in southern Caribbean may develop later this week

An area of disturbed weather (93L), associated with a broad area of low pressure that formed at the tail end of a stalled-out cold front, continues in the south-central Caribbean Sea. The disturbance has a strong potential to develop into a tropical storm by late this week. This morning's QuikSCAT pass missed 93L, but last night's QuikSCAT pass revealed an elongated circulation center near 11N 79W, about 300 miles north of the Panama Canal. Wind shear is a low to moderate 5-15 knots over the disturbance. Visible satellite images show that heavy thunderstorm activity has changed little in coverage or intensity over the past day in association with 93L, and the storm is quite disorganized at present. However, precipitable water imagery shows that the atmosphere has moistened considerably over the south-central Caribbean over the past day, and I expect a marked increase in heavy thunderstorm activity over the region by Tuesday.


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 remainder of the week. 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. However, the SHIPS intensity model does not develop 93L at all.

Steering currents are weak, but a slow west-northwest to northwest motion of 93L is likely beginning on Tuesday, when an intensifying extratropical storm off the east coast of Florida should impart northwesterly steering currents over the southern Caribbean. Most of the models foresee that 93L will move to a point just offshore the Nicaragua-Honduras border by Thursday. At that time, a strong trough of low pressure will be approaching the U.S. East Coast. Most of the models predict that this trough will be strong enough to pull 93L northward towards western Cuba (GFDL and UKMET models), or even northeastwards, towards eastern Cuba and Jamaica (HWRF and ECMWF models). These two models foresee a possible threat to the Bahamas or South Florida late this week or early next week. The GFS model predicts the trough will not be strong enough to turn 93L northwards, and predicts a landfall in Nicaragua late this week. Since this is the outlier, I am discounting this solution, and predict that 93L will remain over water this week, becoming Tropical Storm Paloma Wednesday or Thursday. NHC is giving 93L a medium (20%-50% chance) of developing into a tropical storm by Wednesday morning. I give 93L a 40% chance of eventually becoming a hurricane.

Northeastern Nicaragua and northeastern Honduras are at risk of heavy rains from 93L beginning Tuesday. Total rainfall amounts of 4-8 inches are likely through Wednesday in these countries. Panama and Costa Rica will probably receive about 2-4 inches of rain through Wednesday. Heavy rains will likely move into the Cayman Islands on Wednesday.

I'll have an update Tuesday morning.

Jeff Masters