Time to watch the Western Caribbean

The large upper level low pressure system that has been anchored over the ocean between Bermuda and Puerto Rico the past week has finally begun to lift northwards. As a result, the amount of wind shear over the western Caribbean has begun to drop today, resulting in an increase in thunderstorm activity over a weak low pressure area centered 150 miles southeast of Jamaica. However, there is no edivence of any upper-level outflow setting up, or any low-level spiral banding. The wind shear over the disurbance is still a rather high 10 - 20 knots, which should prevent any tropical development through Friday. However, the global computer models are forecasting this shear to drop below 10 knots by Saturday, which could allow a tropical depression to develop. Now that it is mid-October, the western Caribbean is the primary area we need to be concerned about for tropical storm development. Water temperatures are still very high there, up to 32 C near Jamaica. Historically, the worst hurricanes to form in the last half of October have all been western Caribbean hurricanes.

Any development that occurs this weekend would appear to primarily be a threat to Honduras and Nicaragua, according to the UKMET, NOGAPS, and GFS models. Let's hope the atmosphere is not setting up for a repeat of 1998's Hurricane Mitch, which formed in the western Caribbean in late October and hit Honduras as a Category 5 hurricane, killing over 10,000.


Figure 1. Current Sea Surface Temperatures compiled by NOAA's AOML.

Cape Verdes tropical disturbance
A concentrated are of thunderstorms has developed about 450 miles southwest of the Cape Verdes Islands this afternoon. While there is no surface circulation apparent on satellite imagery yet, some modest upper-level outflow has developed to the north, and the system is headed towards an area of low wind shear. Some further development of this system is possible over the next few days as it tracks west-northwest over the open ocean. Tropical storms devloping this far east in mid-October are never a threat to the Caribbean or North America; only the Azores Islands needs to be concerned about development in this region.

New England
New England, and particularly the New York City region, continues to get soaked by an endless stream of tropical moisture. Several small low pressure areas have formed along the axis of disturbed weather stretching from New York southeastwards towards Bermuda, but wind shear is too high and water temperatures too marginal for any significant tropical development to occur in this region. The axis of the line of disurbed weather is forecast to move slowly northeast in to Maine this weekend, finally bringing an end to the rains.

Jeff Masters