Forecasters said it could bring life-threatening flooding to Southern coastal states.
Thousands of Florida residents evacuated homes on Sunday (May 27) as the storm headed north through the Gulf of Mexico.
The storm was about 115 miles (185 km) southwest of Panama City, on the Gulf of Mexico coast as of 2 a.m. EDT, the U.S. National Hurricane Center said.
Alberto was expected to drop as much as 12 inches (30 cm) of rain, slamming an area from Mississippi to western Georgia, the Miami-based hurricane center said.
After that, it will bring powerful winds and heavy rains as it moves into the Tennessee Valley on Tuesday (May 29) and Wednesday (May 30), the hurricane center said. The storm comes during the Memorial Day weekend and was expected to scramble transportation on Monday as many people return from holiday travel.