Tropical storm Isaac pushed into Cuba today after sweeping across Haiti's southern peninsula, where it caused flooding and at least three deaths.
Isaac's centre made landfall just before midday near the far-eastern tip of Cuba, downing trees and power lines.
Forecasters said Isaac poses a threat to Florida on Monday and Tuesday, just as the Republican Party gathers for its national convention in Tampa.
It could eventually hit the Florida Panhandle as a Category 2 hurricane with winds of nearly 160kph.
Florida Governor Rick Scott declared a state of emergency, officials urged vacationers to leave the Florida Keys and the US National Hurricane Center said a hurricane warning was in effect there, as well as for the west coast of Florida from Bonita Beach south to Ocean Reef and for Florida Bay.
At least three people were reported dead in Haiti. A woman and a child died in the town of Souvenance, Senator Francisco Delacruz told a local radio station.
A 10-year-old girl died in Thomazeau when a wall fell on her, said Marie Alta Jean-Baptiste, director of Haiti's Civil Protection Office.
She said as many as 5,000 people were evacuated because of flooding.
Many, however, stayed and suffered.
The Grive River overflowed north of Port-au-Prince, sending chocolate-brown water spilling through the sprawling shantytown of Cite Soleil, where many people grabbed what possessions they could and carried them on their heads, wading through waist-deep water.
"From last night, we're in misery," said Cite Soleil resident Jean-Gymar Joseph. "All our children are sleeping in the mud, in the rain."
More than 50 tents in a quake settlement collapsed, forcing people to scramble through the mud to try to save their belongings.
About 300 homes in Cite Soleil lost their roofs or were flooded 1m deep, according to Rachel Brumbaugh, operation manager for the US non-profit group World Vision.
