Isaac expected to stay below hurricane force until in Gulf

Tropical Storm Isaac strengthened slightly 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's in the Gulf of Mexico. It's expected to stay to the west of Tampa, Fla., where the Republican National Convention starts on Monday, though there is still an outside 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 landfall near the Alabama-Mississippi border.