Tropical Storm Issac Struggling With Dry Air.

 IR Rainbow Satellite Image Of T.S. Issac At 5:45 AM MDT.

CMISS NHC IR Satellite Image Of T.S. Issac At 5:45 AM MDT.

IR RBTOP Satellite Image Of T.S. Issac At 5:45 AM MDT.

NHC Forecast Track Of T.S. Issac.

Forecast Tracks Of T.S. Issac.

00Z GFS Forecast.
Valid At 6 PM MDT Tuesday Aug 28, 2012.

00Z CMC Forecast.
Valid At 6 PM MDT Monday Aug 27, 2012.

00Z ECMWF Forecast.
Valid At 6 PM MDT Wednesday Aug 29, 2012.

Sea Surface Temperatures.

Update at 9:00 AM MDT-

At 9 AM MDT, Tropical Storm Issac was located near 15.6 N and 65.4 W, or about 200 miles south-southeast of San Juan Puerto Rico. Issac has resumed a course to the west at 15 mph. He still has a large but fairly weak central circulation. His winds are still sustained at 40 mph, with a central pressure of 1003 millibars, or 29.62 inches of mercury. Environmental conditions are favorable for Issac to rapidly intensify, and this may very well happen once the cyclone develops a well defined inner core. NHC forecasters have shifted Issac's forecast track a little further to the west on the 9 AM MDT advisory.

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At 6 AM MDT this morning, Tropical Storm Issac was located near 15.4 N and 64.8 W, or about 225 miles south-southeast of San Juan, Puerto Rico. Issac's is generally moving to the west at 13 mph, although he has recently taken a jog to the southwest overnight. Issac continues to have a broad circulation weak circulation at the surface. He has sustained winds at 40 mph with higher gusts. His central pressure is 1003 millibars, or 29.62 inches of mercury. Tropical Storm Issac is a large cyclone, stretching 1,000 miles across its breadth. 

Tropical Storm Issac continues to battle dry air that is being ingested into the northeastern quadrant of the cyclone at the mid and upper levels. This continued in-gestation of dry air over the past 3-4 days continues to disrupt Issac's inner circulation, and is prohibiting the storm from strengthening into a Hurricane. However, the National Hurricane Center forecast models indicate that this will end within 36 hours, and Issac is still forecast to strengthen into a hurricane by then.

Issac has been jogging to the southwest overnight, and has slowed down in his forward speed. He entered the eastern Caribbean last night as well. Currently Issac is generally moving off to the west at around 13 mph, but there is some doubt from the NHC about this. Issac is forecast to resume a track to the west, and then begin a turn towards the west-northwest. A break in the subtropical ridge of high pressure in about 72 hours over the eastern Gulf of Mexico, and Florida, should allow Issac to make a turn more to the northwest this weekend.

Last nights 00Z computer forecast model run of the European (ECMWF) model has shifted a little more to the east. It appears that the models are trying to tighten up on their consensus of Issac's forecast track. But the jog to the southwest has not only my attention, but others as well. It will be interesting today to see if this jog to the southwest continues, and if so, how much further to the west would Issac move than what the models are forecasting.

There still remains some unknown's concerning Issac's eventual exact track. Again, if Issac tracks across the mountains of Hispaniola and eastern Cuba this weekend, the mountainous terrain in these island nations will significantly disrupt Issac's circulation, and may prevent the storm from becoming too strong, until he re-emerges out over the Florida Keys. If Issac tracks further to the south and west than is currently being forecast, and enters the central Gulf of Mexico the first of next week, then he may have the potential to become a Major Hurricane.

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