It is forecast to drop as much as 30cm (12in) of rain across MS to western Georgia and to bring storm swells of about 60-120cm (2-4ft) to low-lying areas.
A storm surge watch is in place for part of the panhandle from the Suwanee River to Mexico Beach.
A few fast moving storms will dot the landscape but rain bucket totals should not be that great.
After that, it will bring powerful winds and heavy rains as it moves into the Tennessee Valley on Tuesday and Wednesday, the hurricane center said.
The National Weather Service has issued a flash flood watch for Wake, Chatham, Nash and Johnston counties and points south through 8 a.m. Tuesday.
A news release from Florida Gov. Rick Scott said that for Taylor County, "Voluntary evacuations have been issued for those in coastal zones and beach communities (Keaton, Dekel, Cedar, Dark Islands), mobile homes, RV parks and low-lying areas". A more destructive storm could develop over the next 48 hours. Alberto will become the ninth named storm to make landfall on the continental United States before June 1 on record.
US National Hurricane Center (NHC) and state officials requested residents monitor the storm, and make preparations. Just because it's "nice and sunny" after the storm passes, Medlin says there's still a risk for swimmers.
A subtropical storm like Alberto has a less defined and cooler centre than a tropical storm, and its strongest winds are found farther from its centre. Maximum winds were 50 miles per hour. gusting to 65 miles per hour. The storm has maximum sustained winds of 50 miles per hour and the NHC says it is moving north-northwest at 12 miles per hour.
Tropical Storm warnings have has been posted for parts of the northern Gulf Coast and some coastal waters along the western side of FL. "We're talking eight to 12 inches of rain this weekend, and storm surges on the Gulf Coast". The increased threat for severe thunderstorms will also lead to threats of flooding in the metro. Governor Kay Ivey of Alabama declared a state of emergency in 40 counties beginning at 6 a.m.
The storm was about 130 miles west-southwest of Tampa, moving north at 14 mph, the hurricane center said. Alberto will bring widespread heavy rain in the Panhandle of Florida and Alabama later today and tonight.
After making landfall near the Florida panhandle, the storm was expected to continue northwest, slowing down Monday, according to weather.com.