Tropical Storm Isaac battered Haiti on Saturday (local time), leaving at least two people dead, and hit Cuba as Florida braced for a possible hurricane that forced a one-day delay to the Republican convention.
With winds of up to 95km/h, the storm was expected to sweep across Cuba at night and become a hurricane on Sunday as it nears Florida, according to the US National Hurricane Center.
A hurricane warning was in effect for the Florida Keys and parts of the state's southwest coast, the Miami-based NHC said, forcing the disruption of the Republican National Convention which was scheduled to start on Monday (local time) in Tampa.
"Due to the severe weather reports for the Tampa Bay area, the Republican National Convention will convene on Monday August 27th and immediately recess until Tuesday afternoon," Republican National Committee chairman Reince Priebus said in a statement.
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. They were the first two known casualties of 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.
The storm was 195km east of Camaguey, Cuba as it swirled along the coast to the northwest at 33km/h, the NHC said in its latest bulletin.
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.
Local authorities "must understand the possible impact of the intense rain on dams, canals and rivers," the Cuban civil defence office said, warning of blocked water drainage systems and flooded roads.
But officials noted that eastern reservoirs are at very low levels, helping mitigate the risk of flooding.
After striking Haiti and southeastern Cuba, home to the US naval base and "war on terror" prison at Guantanamo Bay, Isaac was on course for a hit at or near the Florida Keys off the southern tip of the US.
The NHC said a tropical storm watch had been issued for the Florida west coast.
Isaac could reach mainland Florida as early as Sunday, ahead of the Republican convention, when tens of thousands of people will be in Tampa for speeches, parties and the formal nomination of former Massachusetts governor Mitt Romney to take on President Barack Obama in November 6 elections.
Tampa Mayor Bob Buckhorn, a Democrat, had 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 before the Republicans announced the one-day delay to the start of the convention proper.
Vice President Joe Biden has canceled a trip to Tampa because of the approaching storm, Obama's Democratic campaign said.
In the Gulf of Mexico, BP evacuated its Thunder Horse platform, the world's largest offshore production and drilling facility.