At 6:50 p.m. EDT, the National Weather Service said Alberto, with maximum sustained winds of 60 mph and higher gusts, was about 140 miles east-southeast of Charleston, S.C., and about 118 miles south of Cape Fear, N.C.
Tropical storm-force winds extended as much as 45 miles from the center of the storm.
Alberto was moving southwest at 3 mph and was expected to continue moving southwest through Sunday before turning toward the west-northwest, then toward the east and northeast by Monday.
No coastal warnings or watches were in effect.
The NWS said a tropical storm watch may be needed Saturday night for portions of the coast of the Carolinas.