PORT-AU-PRINCE, Haiti -- Tropical Storm Isaac strengthened as it spun toward the Dominican Republic and vulnerable Haiti on Friday, threatening to bring punishing rains but unlikely to gain enough steam to strike as a hurricane.
Forecasters now expect the storm to stay below hurricane force until it reaches the Gulf of Mexico, staying to the west of Tampa, Fla., where the Republican National Convention starts on Monday, though there is still a chance it could hit there.
Forecaster Eric Blake of the U.S. National Hurricane Center said it is "too early to know" the storm's exact course, though projections indicated the storm could make U.S. landfall near the Alabama-Mississippi border.
In Haiti, the government and international aid groups announced plans to evacuate several thousand people from one of the settlement camps that sprang up in the aftermath of the 2010 earthquake.
Isaac was expected to dump eight to 12 inches of rain on the island of Hispaniola that is shared by Haiti and the Dominican Republic.
"That kind of rain is going to cause some life-threatening flash floods and mudslides," said Dennis Feltgen, a spokesman for the Hurricane Center in Miami.
Isaac was centered about 90 miles south-southeast of Port-au-Prince, the Haitian capital, on Friday evening.
The center of the storm was expected to pass over Haiti on Friday night.