Authorities say conditions are especially unsafe with flooding rains coming overnight and on a holiday weekend when many people have outdoor plans.
Alberto is the first named storm of the 2018 hurricane season.
Jeffrey Medlin, meteorologist in charge in Mobile, says even after the storm moves north there will still be swells coming up from the south.
Alberto is expected to travel across the eastern Gulf of Mexico Saturday night through Monday and approach the northern part of the Gulf where it could make landfall Monday night.
Florida declares state of emergency over Subtropical Storm Alberto
Florida and MS launched emergency preparations Saturday ahead of the arrival of Subtropical Storm Alberto, a slow-moving system expected to cause wet misery across the eastern U.S. Gulf Coast over the holiday weekend.
Alabama Gov. Kay Ivey issued a state of emergency for 40 counties, starting at 6 a.m. Sunday.
Meteorologists expect a turn toward the north-northwest at a slower speed into Sunday.
The expected impact on the Mississippi Coast has lessened, and the storm surge watch has been canceled for the three coastal counties. A tropical storm watch and flash flood watch remain in effect.
Landfall is most likely in the Florida Panhandle, maybe before sunrise near Apalachicola, or as late as the evening it were to take a more westward track to Pensacola.
Cuba is expected to get as much as 15 inches of rain, the National Hurricane Centre said.
There are expected to be no big issues from Alberto for southeast Louisiana.
The projected path keeps the center of the storm west of NCFL.
Florida's Governor, Rick Scott, has also declared a state of emergency.
Rain bands are rotating into South Carolina, Georgia, Alabama, and Florida this afternoon with tropical storm force wind gusts being experienced across parts of Florida as Alberto moves to the northwest at 10 miles per hour. At this hour, Alberto has strengthened and now has maximum sustained winds of 65 mph and pressure is down to 991 mb.