A hurricane watch means hurricane conditions are possible within 36 hours.
Forecasters have said the storm, which could grow to a Category 1 hurricane, could threaten South Carolina's north coast early Saturday.
The weather service says tropical storm force winds could reach the state's northern coast by Friday afternoon and tides could be up to four feet above normal. The worst of the weather should be early Saturday.
Emergency officials in South Carolina are closely watching the storm and say there will be time to evacuate if needed.