The storm's failure to gain the kind of strength in the Caribbean that forecasters initially projected made it more likely that Isaac won't become a hurricane until it enters the Gulf of Mexico, said Eric Blake, a forecaster with U.S. National Hurricane Center in Miami.
"We think it could become a hurricane on Monday," Blake said late Thursday. "It would be somewhere over the Gulf of Mexico."
At 8 a.m. the National Hurricane Center reported that the hurricane hunter aircraft reports that Isaac is a little stronger, with sustained winds reaching 50 m.p.h. The center of Isaac will move near or over the island of Hispaniola (Haiti and the Dominican Republic) today...And move near or over southeastern Cuba on Saturday.
The latest five-day forecast showed the storm's path shifting to the west, possibly making landfall near the Alabama-Mississippi border, Blake said. But he said it was "too early to know" the exact course and stressed that Florida's Gulf Coast, including Tampa, the site of next week's Republican National Convention, was still in the forecast cone.
The storm dumped heavy rain Thursday across eastern and southern Puerto Rico and whipped up waves as high as 10 feet (3 meters) in the Caribbean as it churned across the region.
Early Friday, Isaac was centered about 165 miles (265 kilometers) south of Santo Domingo, Dominican Republic, and had maximum sustained winds of 45 mph (75 kph). It was moving west near 15 mph (24 kph), according to the hurricane center.
In flood-prone Haiti, Prime Minister Laurent Lamothe urged people to avoid crossing rivers, to tape their windows, and to stay calm, saying "panic creates more problems."
Lamothe and other Haitian officials said the government had set aside about $50,000 in emergency funds and had buses and 32 boats on standby for evacuations.
But among many Haitians, the notion of disaster preparedness in a country where most people get by on about $2 a day was met with a shrug.
"We don't have houses that can bear a hurricane," said Jeanette Lauredan, who lives in a tent camp in the crowded Delmas district of Port-au-Prince.
About 400,000 people remain in settlement camps comprised of shacks and tarps in the wake of Haiti's devastating 2010 earthquake.
So far, Isaac itself had caused no reported injuries or deaths, but police in Puerto Rico said a 75-year-old woman died near the capital of San Juan on Wednesday when she fell off a balcony while filling a drum with water in preparation for the storm.
In the Dominican Republic, authorities began to evacuate people from low-lying areas but encountered resistance.
"Nobody wants to leave their homes for fear they'll get robbed," said Francisco Mateo, community leader of the impoverished La Cienaga neighborhood in Santo Domingo, the capital.
The Dominican government planned to close all of the country's nine airports by dawn Friday, said Alejandro Herrera, civil aviation director. Schools closed by Thursday afternoon.
The storm's approach prompted military authorities at the U.S. base in Guantanamo Bay, Cuba, to cancel pretrial hearings for five prisoners charged in the Sept. 11 terrorist attacks. They also evacuated about 200 people, including legal teams and relatives of Sept. 11 victims.
Blake, the U.S. forecaster, said that while Isaac hadn't strengthened much in the Caribbean, it could gain power as it moves away from Cuba. "When it moves back over water, it has a chance to restrengthen," he said.
Organizers of next week's Republican National Convention in Tampa were working closely with state and federal authorities on monitoring storm as they prepared for the arrival of 70,000 delegates, journalists and protesters.
"We continue to move forward with our planning and look forward to a successful convention," convention CEO William Harris said in a statement.
Out in the eastern Atlantic, another tropical storm, Joyce, was downgraded to a tropical depression late Thursday, and posed no threat to land. The hurricane center in Miami said Joyce had maximum sustained winds of 35 mph (55 kph) and that it was becoming disorganized.
Associated Press writers Trenton Daniel in Port-au-Prince, Haiti; Tamara Lush in Tampa, Fla.; Steve Peoples in Washington; and Ezequiel Abiu Lopez in Santo Domingo, Dominican Republic, contributed to this report.
Copyright 2012 The Associated Press.