Storm Gradually Gains Strength On Friday As It Nears Hispaniola

Tropical Storm Isaac is gradually gaining strength as it moves through the Central Caribbean toward the southwestern coast of Haiti on this Friday night. The storm, which still remains somewhat disorganized thanks to some dry air getting into its western flank, has been slowly strengthening all day today with winds increasing to 60 miles per hour by 11:00 AM EDT, and then going up to 65 miles per hour by 5:00 PM EDT.

Maximum sustained winds with Isaac remain at 65 miles per hour with gusts of minimal hurricane force. Minimum central pressure is down to 29.29 inches of Hg or 992 millibars, which is actually down two millibars from the late afternoon advisory.

The satellite imagery shows a storm that has done a bit of a 360 in the past 24 hours or so. Yesterday at this time, much of the convection was on the western side of the storm. Now, it is on the usually more stronger eastern side. There is good outflow, or exhaust from the storm except for the northwestern part, and that is where the dry air appears to be getting into the system. There has been a trough to the west of Isaac as well, and that may be contributing to the storms continued struggles. Now, it is beginning to interact with the rugged terrain of Hispaniola, which has mountains as high as 10,000 feet on the Dominican Republic side.

The interaction between these mountains and Isaac will cause orographic lifting of the tropical air to take place, and that will cause tremendous condensation and torrential rains. Streams of moisture have already been flowing into the southern portion of the Dominican Republic. Those rains and more are expected to impact Haiti, where many are still living in tents around Port Au-Prince following the deadly and devastating earthquake there several years ago. Currently, Isaac is located some 165 miles south-southwest of Santo Domingo, the capital of the Dominican Republic, or about 185 miles to the south-southeast of Port Au-Prince.

The big story is that the storm has slowed down, which also adds to the fears of significant flooding and mudslides across Haiti and the Dominican Republic. The National Hurricane Center has Isaac currently moving at 10 miles per hour, which is down from 16 miles per hour just a few hours ago. Consequently, the NHC is forecasting some 8 to 12 inches of rain for Hispaniola with some areas receiving 20 inches. Further to the west across Cuba and even Jamaica, some 4 to 8 inches are expected with isolated areas getting up to a foot of rain. Puerto Rico is still receiving rain, and could get up between 2 to 4 inches with some remote locations seeing 6 more inches.

There are a lot of watches and warnings out for this storm. Currently a Hurricane Watch is in effect for Haiti. A Tropical Storm Warning is in effect for the Dominican Republic, Haiti, the Cuban provinces of Ciego de Avila, Sanctus Spiritus, Villa Clara, Camaguey, Las Tunas, Granma, Holguin, Santiago de Cuba, and Guantanamo, Andros Island in the Bahamas, the Central Bahamas including Cat Island, The Exumas, Long Island, Rum Cay, and San Salvador, the Southeastern Bahamas including the Acklins, Crooked Island, Long Cay, the Inaguas, Mayaguana, and the Ragged Islands as well as the Turks and Caicos.

Tropical Storm Watches were first issued for the United States mainland during the 5:00 PM EDT Advisory. Now, they are in effect for the provinces of Matanzas and Cienfuegos in Cuba, Jamaica, the Northwestern Bahamas including the Abacos Islands, the Berry Islands, Bimini, Eleuthera, Grand Bahama Island, and New Providence, the Florida Keys including the Dry Tortugas, the East Coast of Florida south of Jupiter Inlet, the West Coast of Florida south of Bonita Beach, Florida Bay and Lake Okeechobee.

Looking at the most recent model runs of the GFS, GFDL, ECMWF, and HWRF, there is a general northwestward track with the GFS being the furthest east, and the ECMWRF being the furthest west but they all show an impact in South Florida, and a second landfall somewhere along the Gulf Coast.

The latest GFDL model run has Isaac moving across the southwestern coast of Haiti into the narrow channel between Hispaniola and Cuba, traveling over the spine of Cuba and impacting the Florida Keys and South Florida before moving over water again in the Gulf, and eventually making a final landfall in the Florida Panhandle.

The GFS, which actually did a fairly decent job last week of projecting that the storm would be in the general vicinity of the Eastern Caribbean at about this time, has Isaac going across southwestern Haiti, but then going further to the north into the Southeastern Bahamas and more of South Florida before exiting into the Gulf, and eventually making a second U.S. landfall in the Pensacola, Florida and Mobile Bay, Alabama area.

The ECMWF has a more western track that goes across more Cuban real estate before emerging into the Gulf and making a U.S. landfall along the Mississippi and Alabama coasts. Finally, the HWRF has a smaller storm following a similar path of the GFDL across Haiti, along the spine of Cuba and over portions of South Florida, back out into the Gulf, and making landfall in the Pensacola, Florida area.

However, those in Western Florida including Tampa where the Republican National Convention is being held, should pay close attention to the track and progress of this storm since that area is not out of the woods just yet. The cone of uncertainty has not changed much during the day on Friday, and there are still areas along the West Coast of the Sunshine State that could be impacted by this storm.

The 5:00 PM EDT forecast discussion by the NHC is still calling for Isaac not to strengthen much over the next 12 hours, and it will likely weaken as it encounters the high terrain of Hispaniola and Cuba over the next 36 hours. After that, the storm should strengthen as it enters the Florida Straits and Gulf Coast, and become a strong Category One storm with 85 mile per hour winds.