Tropical Storm Isaac lashed Haiti on Saturday with torrential downpours that flooded the already-battered capital, Port au Prince, with at least 30 centimeters of rain.
Early reports said three people were dead, as rescue workers scrambled to aid thousands of residents marooned in tent cities since a massive earthquake devastated the city nearly three years ago.
A statement late Saturday from the U.S. National Hurricane Center placed the storm over eastern Cuba, moving to the northwest at about 30 kilometers an hour. It is expected to gain hurricane force as it moves toward the Florida Keys, the Gulf of Mexico and the U.S. mainland Sunday.
The center has issued hurricane warnings for the west coast of Florida that includes the city of Tampa -- the site of next week's four-day Republican national convention.
Forecasters say it is not yet clear what impact the storm might have on the four-day event. Tampa is more than 300 kilometers north of Miami, Florida's southernmost major city.
In the Haitian capital, Red Cross worker France Hurtubise said most tents held up at one camp, but some were damaged.
"The populations are extremely worried because some of the tents are leaking, so we have to respond to this which is quite urgent," Hurtubise said.
She also voiced concern about the potential for mudslides on the area's vulnerable population.
Some information for this report was provided by AFP and Reuters.