Looks like Gamma is here

Tropical Depression 27 has improved significantly in its appearance on visibile satellite imagery the past few hours, and it is very likely that this storm will be upgraded to Tropical Storm Gamma at 4 pm. The storm's deep convection has increased and now covers the circulation center, and an impressive spiral band has formed to the south. Satellite intensity estimates from The University of Wisconsin's CIMSS estimate that this is a 1000 mb tropical storm with 50 mph winds. Wind shear has dropped from 25 knots to about 20 knots this morning, which is still high enough to prevent anything more than slow strengthening. The remainder of this morning's discussion appears below, unchanged.

We've seen two systems in the past month, Wilma and Alpha, survive and even intensify in the face of high wind shear. TD 27 has already shown the ability to exist in a highly sheared environment, and I expect it will hold together long enough to take advantage of the lower wind shear expected to develop over the Carribean by Wednesday. The eventual intensity of TD 27 will be highly dependent on its track. If the storm stays in the northern portion of the Caribbean, where wind shear is strong, TD 27 will probably never strengthen to more than a tropical storm. However, if TD 27 can track further south through the southern Caribbean, wind shear is expected to be much lighter. Ocean temperatures are warm enough to allow a hurricane to form, and the GFDL model predicts TD 27 will intensify into a major Category 3 hurricane by the end of the week.

The computer models did not initialize TD 27 very well in their runs that we have available this morning, so our confidence in the long-term track of TD 27 is low. All the models agree on the basic idea that TD 27 will track westward over the Caribbean for the next five days, under the steering of a strong ridge of high pressure. By the end of the week, the models begin to diverge, with the GFS, NOGAPS, and GFDL models strengthening the ridge further, driving TD 27 into Nicaragua or Honduras. The UKMET and Canadian models disagree, and forecast that a trough of low pressure will turn TD 27 northwards in the vicinity of Jamaica and the Cayman Islands. TD 27 would then get caught in strong westerly winds, cross Cuba, then scoot through the Bahama Islands to the northeast. No model is indicating that TD 27 will threaten the U.S. mainland, and the storm would have to walk a very narrow tightrope to make it all the way to Florida. With such strong westerly winds blowing across Cuba and the Florida Straights, TD 27 will very quickly recurve away from the U.S. once it gets as far north as Jamaica's latitude.

The Hurricane Hunters are scheduled to make their first flight into TD 27 Tuesday afternoon.

I'll be back with an update late this afternoon when the 7am EST (12Z) model runs are available.

Jeff Masters