Tropical Storm Isaac has hit the impoverished Caribbean nation of Haiti.

The storm touched down early Saturday with near hurricane strength west of Port-au-Prince, the capital.

Long lines were seen outside supermarkets Friday in Port-au-Prince, a locale where 400,000 people have lived in tent camps since an earthquake devastated the capital city nearly three years ago. President Michel Martelly has urged Haitians to heed civil defense advice.

Aid groups have prepared clean water and hygiene kits to help prevent the spread of cholera, which Haiti has struggled to control since the earthquake.

There is a potential for deadly flash floods and mudslides in Haiti because so much of the country is deforested.

Organizers of next week's U.S. Republican National Convention in Tampa, Florida are keeping a watchful eye on Isaac. Forecasters say it is not yet clear what, if any, impact the storm will have on the four-day event on Florida's Gulf coast.

Computer models show Isaac approaching the southern tip of Florida by Monday, making landfall somewhere between the Florida panhandle, in the northwestern part of that state, and New Orleans, Louisiana, farther west on the Gulf of Mexico.

New Orleans and other parts of the Gulf were devastated by Hurricane Katrina in 2005.