Forecasters said it could bring life-threatening inundation to Southern coastal states. Destin and Panama City Beach are within the watch area.
Alberto's top winds jumped to 65 miles (105 kilometers) per hour, which will probably be as strong as it gets, wrote Richard Pasch, a meteorologist at the National Hurricane Center in Miami. The threat of storms through the end of the week makes this a definitely possibility.
Flooding is seen in Ellicott City, Maryland, U.S. May 27, 2018, in this still image from video from social media.
Subtropical Storm Alberto was moving northward through the Gulf of Mexico on Sunday.
Hurricane season doesn't officially begin until June 1, but Alberto apparently missed the memo.
Alberto could cause $400 million to $500 million across the region, including damage to cars crushed by toppled trees, wrecked roofs and flooding, Watson said in an interview.
Tropical Storm Warnings continue for almost the entire Gulf Coast of Florida, and a Storm Surge Watch continues for coastal regions from the Nature Coast to Pensacola. The storm comes during the Memorial Day weekend and was expected to scramble transportation on Monday as many people return from holiday travel. While coastal areas may get from 3 to 6 inches of rain, the Florida panhandle into much of Alabama and western Georgia may see 4 to8 inches with isolated storm totals of 10 to 12 inches.
A water spout, a unsafe vortex of wind and water, was spotted late Sunday about 7 miles off shore of Alligator Point, Florida, said Roth.
Mandatory evacuations were ordered for small barrier islands in one northern Florida county, and voluntary evacuations were issued for another.
All 67 Florida counties were issued the emergency notice to give state and local governments enough time and resources to prepare, Florida Governor Rick Scott said in a statement.
"The track of these storms can change without notice", Scott said.
MS governor Phil Bryant has declared a state of emergency as the storm moves toward the state's coast. Because of this, much of North Carolina is under a Flash Flood Watch. Skies will remain a mix of sun and clouds again throughout the day and southerly winds will keep moisture in the area making for a muggy feeling day as well. Royal Dutch Shell Plc, Exxon Mobil Corp and Chevron Corp have evacuated some personnel from offshore Gulf oil facilities.
In Gulf Shores, Ala., webcams showed beaches beginning to fill up as the storm's track shifted slightly east away from the region, but red flags on the beach warned beach-goers to stay out of the rough water.
The National Weather Service projects Alberto will hit Alabama starting Saturday, with the state's heaviest rains falling closer to the coast, through the middle of next week.