Whether Isaac skirts the Gulf or Atlantic coasts or makes landfall, the storm is large enough that its outer bands will likely be felt somewhere in South Florida, Berg said.
In the Caribbean, Haiti’s Office of Civil Protection and National Meteorological Center warned residents in flood-prone areas to monitor the radio and "remain vigilant."
In advance of the storm, Puerto Rico suspended classes Wednesday and closed all government offices except those engaged in emergency operations and the governor declared a state of emergency.
Eight flights were canceled from San Juan to neighboring Caribbean islands. The airport was not expected to close Thursday although airlines could cancel flights.
Warning Coordinator Meteorologist Ernesto Morales said the storm’s outer bands were already being felt in the afternoon, with gusts of up to 37 mph detected at San Juan’s airport about 5 p.m. Wednesday. He said the storm promises plenty of rain island-wide, from four to six inches and up to 10 inches possible in some areas.
In Cuba, the Pentagon is evacuating about 200 people -- lawyers, staffers, 911 victims -- from the U.S. Navy base in Guantánamo on Thursday in advance of the arrival of Isaac at Guantánamo. They all were brought to the base earlier this week for a hearing in the Sept. 11 terror trial that the judge cancelled in consideration of the storm.
The Cuban Institute of Meteorology also put out advisories about the storm and Radio Havana Cuba reported that Isaac "represented a potential danger to the island,’’ but for the most part, the Cuban media stuck to disseminating the advisories. The closest Cuban city to the storm track is Baracoa on the mountainous eastern tip of the island, just across the Windward Passage from Haiti. The last time Baracoa was affected by a hurricane was Nov. 5, 2010, when Hurricane Tomas passed just east of the small city with 80 mph winds and caused a minor storm surge.
Miami Herald staff writers Jacqueline Charles and Carol Rosenberg, reporting from Guantánamo, contributed to this story.