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Posted at 12:15 PM ET, 08/23/2012

Isaac weaker, but expected to become hurricane tomorrow


Enhanced infrared satellite image of Tropical Storm Issac from 10:15 a.m. EDT. (CIRA/RAMMB)

Since yesterday, Isaac has weakened a little, and as of 11 a.m. EDT today, has 40 mph sustained winds. The center is located about 200 miles south of Puerto Rico, but tropical storm-force winds extend out to 140 miles from the center. It is forecast to reach hurricane status on Friday as it approaches Hispaniola.

Tropical storm warnings cover the Virgin Islands, Puerto Rico, and the north coast of the Dominican Republic, while hurricane warnings are in effect for the south coast of the Dominican Republic and all of Haiti. A tropical storm watch is also now in effect for the eastern Bahamas. For the latest watches and warnings, see the NHC website. To help track the storm in real-time, I have some radar loops available of Isaac, and will be adding more as it moves into their range.

The track forecast remains largely unchanged from prior advisories. Isaac is forecast to slowly make a turn to the west-northwest today and head toward the mountainous island of Hispaniola (home to Dominican Republic and Haiti). Whether it scrapes over the entire island or just brushes by will certainly have a large influence on the subsequent intensity. It should then reach eastern Cuba by early Saturday, and exit back over the Florida Strait early on Sunday.

After about a day over the warm ocean, it will be on south Florida’s doorstep. The exact details of whether it’s the eastern or western side of the peninsula, or just offshore, are impossible to know this far out.

What’s important is that people prepare for a hurricane and hope for less. Conditions in southern Florida will turn for the worse on Sunday and the worst of the weather will be on Monday... even if the storm’s center misses land. Of course, if it misses south Florida, that means it will have another 1-2 days over the very warm eastern Gulf of Mexico as it heads for MS, AL, the FL panhandle, or the western FL peninsula as a potentially stronger hurricane. Model guidance is fairly tight, but even a small amount of spread represents a big difference in landfall location in this case.


Forecast tracks from a variety of models, going out 5-7 days (UW-Milwaukee.)

Republican National Convention

This storm will have a large impact on the Republican National Convention being held in Tampa next week. It’s certainly possible that air travel into Tampa will be hindered in the Sunday-Wednesday timeframe, in addition to the strong winds, heavy rain, and possible storm surge during the event. As of this morning, Tampa has a 24% chance of experiencing tropical storm-force winds, and a 1% chance of experiencing hurricane-force winds in the next five days.

The city is also very prone to storm surge due to its location at the end of a bay... and the convention center is rather poorly sited for surge: right on the far tip of the bay where water has nowhere else to go, and not even 200 feet from the water’s edge. It is in Zone B for evacuations (with A being extremely low-lying and highest-risk, and E being at-risk only from very strong storms).


Map of the Tampa area with the RNC location tagged under the marker (Google Maps.)

To help with the track and intensity guidance, three aircraft are conducting reconnaissance missions into and around Isaac today: an Air Force C-130 based out of St. Croix, the NOAA P-3 based out of Barbados, and the NOAA G-IV based out of Tampa. The G-IV aircraft is used for large-scale sampling of the atmosphere upstream of the storm, while the other two planes actually fly into the storm to gather data on its location and intensity. The NOAA flight paths shown here give you an idea of the types of patterns these different aircraft fly.


Proposed flight paths for the NOAA G-IV and the NOAA P-3 today to investigate Isaac and its environment. (NOAA/AOML/HRD)

Tropical Storm Joyce

Further east, Joyce, the tenth tropical storm of the season, formed about 1300 miles due east of the Leeward Islands at 11 a.m. today (this was Tropical Depression 10). This storm will most likely not be a threat to land at all... it’s expected to recurve to the north well before even reaching the Caribbean. In an average season, we would normally reach the 10th named storm on October 19, so this season is almost certainly going to be far more active than average. And we have not had a major hurricane yet, but climatologically, we don’t until the first week of September.

The author, Brian McNoldy, is a senior researcher at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science, and also maintains his own blog.

By Brian McNoldy  |  12:15 PM ET, 08/23/2012

Categories:  Tropical Weather, Latest

 
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