Tropical storm watches are up already for both the west and east coasts of Florida, as Tropical Storm Isaac bears in on Haiti.
Forecasters expect landfall on Haiti's southern peninsula Friday night, bringing punishing rains. They say it's unlikely to gain enough steam to strike as a hurricane.
Government and international aid groups in Haiti's capital are prepared to evacuate thousands of people still living in the camps that sprang up in the aftermath of the 2010 earthquakes.
The National Hurricane Center in Miami says Isaac is likely to stay below hurricane force as it makes its way across the Florida Keys. Once it reaches the Gulf of Mexico on Sunday, however, forecasters say it's likely to gain strength and could develop into a hurricane.
Meanwhile, organizers of next week's Republican National Convention in Tampa said they are monitoring the storm. Some 70,000 delegates, journalists and protesters are expected, and Florida Gov. Rick Scott said there are no plans to cancel the convention.