Wet subtropical storm possible for Florida this weekend

A large low pressure system with heavy rains is expected to develop over Cuba and South Florida on Saturday. The counter-clockwise flow around this low will bring strong winds and heavy rains to much of the Florida coast on Saturday, and these conditions will spread northwards to Georgia by Sunday and South Carolina by Monday. Most of the models develop this system into a tropical or subtropical storm, but the potential location of such a storm is still murky. The ECMWF model predicts the storm will form in the eastern Gulf of Mexico on Monday, then move north into the Florida Panhandle on Tuesday. If this track verifies, the oil rigs off the coast of Southeast Louisiana may experience a one or two day period of sustained winds above tropical storm force Monday or Tuesday. The GFS and NOGAPS models put the storm on the other side of Florida, over the Northwestern Bahamas, and predict the storm will move northwards and hit North Carolina on Wednesday. The UKMET model is in-between, developing the storm right on top of Florida. Since the storm is going to be getting its start as a cold-cored upper-level low pressure system with some dry air aloft, it will probably start out subtropical, with a large band of heavy rain developing well north of the center, bringing heavy rains to a wide region of the Southeast U.S. Subtropical storms cannot intensify quickly, due to their lack of an organized inner core. If the storm follows the path of the GFS model, it could be similar to Subtropical Storm Four of October 4, 1974. That storm brought 10 - 14 inches of rain to the east coast of Florida and strong onshore winds of 30 - 40 mph that caused beach erosion and coastal flooding. The extended forecast discussion from NOAA's Hydrometeorological Prediction Center has a more technical discussion of this coming storm for those interested.


Figure 1. Rainfall forecast for the 5-day period ending at 8 am EDT Monday, October 10, 2011. The storm system affecting Florida this weekend is expected to bring up to 7 inches of rain along the coast. Image credit: NOAA/HPC.

Tropical Storm Philippe no threat to land
In the middle Atlantic, Tropical Storm Philippe is about to interact with a frontal system and turn northeastward out to sea. Satellite loops show Philippe is a small system with a modest amount heavy thunderstorm activity, with the surface circulation partially exposed to view by wind shear. Wind shear will remain in the moderate range today, which may allow the storm to intensify into a hurricane, as predicted by several of the intensity forecast models. By Thursday, wind shear will rise to a very high 30 - 50 knots, which should cause rapid weakening. Philippe will not trouble any land areas.


Figure 2. Morning satellite image of Tropical Storm Philippe. The band of clouds to the northwest of Philippe is associated with a cold front that is expected to absorb the storm and recurve it to the northeast on Thursday.

Jeff Masters