* Hurricane warning in effect for Florida Keys
* Isaac kills one, threatens heavy flooding in Haiti
* Hundreds of thousands of quake survivors still in tent camps (Updates with death, flooding, other detail)
By Susana Ferreira
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.
Heavy rains and high winds lashed Haiti's southern coast, flooding parts of the capital Port-au-Prince, and flattening tents in some of the fragile resettlement camps that house more than 350,000 survivors of the 2010 earthquake.
A 10-year-old girl was killed in Port-au-Prince when a wall fell on her, the Civil Protection authority said. Power outages and flooding were reported as Isaac moved across the hilly and severely deforested Caribbean country.
"There's a lot of rain, a lot of wind," said Magdala Jean-Baptiste, who huddled with her frightened children in their home in the southern coastal city of Jacmel. "We haven't had any power since the storm started yesterday. We passed the night with no sleep."
Isaac was forecast to sweep over eastern Cuba on Saturday and strengthen into a hurricane as it approaches the Florida Keys. It was on track for the Gulf of Mexico, where major energy companies have begun offshore evacuations that could end up shutting nearly half the area's oil output.
The center of Isaac was about 95 miles (150 km) east-southeast of Guantanamo Bay, Cuba, on Saturday morning, the U.S. National Hurricane Center said.
A hurricane warning was in effect for the Florida Keys and 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.
In the Dominican Republic, Isaac felled power and phone lines and left at least a dozen towns cut off by flood waters. The most severe damage was reported along the south coast, including the capital Santo Domingo, where more than half the city was without power.
In Haiti, the United Nations mission there said it was prepared to distribute food and emergency supplies for more than 300,000 people, and 5,700 U.N. troops stood ready to clear roads for emergency response teams.
The government and aid groups tried to evacuate 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).
REFUGE FROM THE STORM
Volunteers from the government's Civil Protection office were sent across Haiti, warning people about flood and landslide risks. About 1,250 shelters opened in schools, churches and other buildings but Red Cross officials said the number could be grossly inadequate. 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.
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.
After crossing Cuba and the Florida Keys, Isaac was forecast to move north to northwest through the Gulf of Mexico and make landfall anywhere on the U.S. coast from the Florida Panhandle to New Orleans at midweek.
Emergency managers urged tourists to leave the Keys if they could do so safely on Saturday. A single road links the chain of low-lying islands to the Florida Peninsula.
Officials said Key West International Airport will stop commercial air traffic on Saturday evening and all day Sunday.
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.