Tropical Storm Isaac emerged over warm Caribbean waters on Saturday slightly weaker but ready to regroup after dumping torrential rains on Haiti, where thousands of people remain homeless more than two years after a devastating earthquake.

The storm was forecast to sweep over eastern Cuba on Saturday and strengthen into a hurricane as it approaches the Florida Keys on a track toward the Gulf of Mexico.

Lashing rains and high winds were reported along parts of Haiti's southern coast and in the capital Port-au-Prince, where more than 350,000 survivors of the 2010 earthquake are still living in fragile tent and tarpaulin camps.

Intermittent power outages affected the greater Port-au-Prince area early on Saturday as Isaac moved across hilly inland areas of the severely deforested Caribbean country.

The center of Isaac was about 95 miles east-southeast of Guantanamo Bay, Cuba, early Saturday morning, the U.S. National Hurricane Center (NHC) said.

A hurricane warning was already in effect in the Florida Keys, but the NHC said it was extending this to part of the southwest coast of Florida.

Isaac's march across the Caribbean comes as U.S. Republicans prepare to gather in Tampa, on Florida's central Gulf Coast, for Monday's start of their national convention ahead of the November presidential election.

The convention is expected to proceed as planned but Gulf of Mexico operators began shutting down offshore oil and gas rigs on Friday ahead of the storm.

The biggest immediate concern was heavily deforested Haiti, where Isaac's rains could trigger deadly flash flooding and mudslides.

The Haitian government and aid groups evacuated thousands of tent camp dwellers on Friday but many Haitians chose to remain in their flimsy, makeshift homes, apparently fearing they would be robbed, said Bradley Mellicker, head of disaster management for the International Organization for Migration (IOM).

"There's a lot of people who are resisting because they are scared of losing what little they have now," Mellicker said.

REFUGE FROM THE STORM

About 3,000 volunteers from the government's Civil Protection office were sent across Haiti, warning people about flood and landslide risks. About 1,250 shelters - schools, churches or other community buildings - opened their doors to house people seeking refuge from the storm.

But Red Cross officials said the number of shelters could be grossly inadequate and Prime Minister Laurent Lamothe acknowledged Haiti had "limited means" to ensure public safety.

Red Cross and IOM representatives joined government officials in trying to evacuate 8,000 of the "most vulnerable people," including 2,500 sick and disabled, from 18 tent camps in low-lying coastal areas of Port-au-Prince.

Many Haitians, most of whom scrape by on less than $1 per day, consider disaster an inevitable part of life in the poorest country in the Americas.

"We live under tents. If there's too much rain and wind, water comes in. There's nothing we can do," said Nicholas Absolouis, an unemployed 34-year-old mechanic at one camp for homeless people on the northern edge of the chaotic capital.

"There are still too many people living in the camps. There's a good chance that those might be destroyed with the passage of the cyclone," said France Hurtubise of the International Federation of Red Cross and Red Crescent Societies in Haiti.

Flooding could also help reignite a cholera epidemic, which has killed more than 7,500 people in Haiti since the disease first appeared in October 2010, foreign aid workers said.

The NHC said Isaac's exact path was uncertain but there was little change to its earlier forecast that the storm would hit Cuba and the southern tip of Florida before moving across the Gulf of Mexico and making landfall anywhere from the Florida Panhandle in the northwest of the state to Alabama and as far west as New Orleans.

The storm's anticipated path had shifted closer to the Keys than previously forecast and emergency managers urged tourists to leave the islands if they could do so safely. A single road links the chain of islands to the Florida Peninsula.

Isaac has drawn especially close scrutiny because of the Republican Party's convention, a four-day meeting during which former Massachusetts Governor Mitt Romney will receive the party's presidential nomination.

Party officials insist the convention will go ahead, even if they have to alter the schedule. But NHC meteorologist Rick Danielson said late on Friday that Tampa could be hit by coastal flooding and driving winds or rain.

"There is still a full range of possible impacts on Tampa at this point," he said.