A hurricane warning was in effect for the Florida Keys and parts of the state's southwest coast
Tropical Storm Isaac barreled toward Florida and was predicted to become a hurricane on Sunday, forcing a one-day delay to the Republican convention, after leaving four people dead in Haiti.
With winds reaching 60 miles (95 kilometers) per hour, the storm left Haiti and swept across Cuba late Saturday, as the Miami-based US National Hurricane Center reported it would probably reach Florida within 24 hours.
A hurricane warning was in effect for the Florida Keys and parts of the state's southwest coast and the Republican Party announced that severe weather warnings had prompted a postponed start to its four-day gathering in Tampa. The proceedings will now start on Tuesday afternoon instead of Monday.
At 0000 GMT, the storm was around 375 miles east-southeast of Key West, Florida and it was moving northwest at 20 miles per hour, with forecasts suggesting it would strengthen over the next 48 hours, the NHC said.
Tens of thousands of Republicans will be in Tampa for speeches, parties and the formal nomination of former Massachusetts governor Mitt Romney as the candidate to take on President Barack Obama in November 6 elections.
Romney said the delay was necessary given the risk to life and limb.
"The safety of those in Isaac's path is of the utmost importance. I applaud those in Tampa making appropriate schedule changes," he said.
Tampa Mayor Bob Buckhorn, a Democrat, had earlier sought to calm jitters about the weather, saying the storm might bring heavy rain to Tampa on the first of the four-day convention but would be followed by sunny skies.
"There may be wet shoes, but every day after Monday ought to be fine," Buckhorn told Fox News.
Vice President Joe Biden canceled a trip to Tampa and other Florida cities because of the approaching storm, Obama's Democratic campaign said.
And in the Gulf of Mexico, BP evacuated its Thunder Horse platform, the world's largest offshore production and drilling facility.
Forecasters earlier said Isaac was near hurricane strength when the eye of the storm passed over Haiti, where hundreds of thousands of people are still living in squalid, makeshift camps following a catastrophic 2010 earthquake.
An eight-year-old Haitian girl died when a wall collapsed at her home and a 51-year-old woman died when her roof collapsed, according to officials, who later said two other people had died in the storm.
Haiti was the poorest country in the Western Hemisphere even before the earthquake killed 250,000 people, and 400,000 citizens are still living in tent camps in and around the devastated capital Port-au-Prince.
More than 3,300 families had been evacuated to temporary shelters ahead of Isaac as aid groups provided clean water and hygiene kits to try to limit the risk of contaminated water and the spread of disease.
Cuba declared a state of alert in the island's six eastern provinces, where nearly five million people live, and evacuated around 5,000 foreign and local tourists from beachside hotels.