"Heavy rains and gusty winds continue to spread northward over Florida", tweeted the account.
Federal officials with the Gulf Islands National Seashore - a group of barrier islands in the Gulf of Mexico - say that ahead of Alberto's arrival, "All Florida areas remain closed, including Hwy". Florida Gov. Rick Scott, Mississippi Gov. Phil Bryant and Alabama Gov. Kay Ivey declared states of emergency.
The governors of Florida, Alabama and MS all declared states of emergency ahead of the storm.
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.
The rain will continue from Monday evening, overnight, into Tuesday morning.
Rain falls on Clearwater Beach by Pier 60 early Sunday morning May 27, as northbound Subtropical Storm Alberto looms in the gulf to the southwest.
The National Hurricane Center says that Alberto now has top sustained 2inds of 65 miles per hour (100 kph) but that little further strengthening is expected before Alberto reaches the Gulf Coast sometime Monday.
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National Weather Service Meteorologist Ryan Rogers said the storm would be "coming very close to shore" around 8 a.m. Monday and make landfall around noon. In some cases, rainfall could top 10 inches in pockets across the state.
In addition to parts of the southeastern US, the heavy rains and storm conditions could produce "life-threatening flash floods and mudslides" in Cuba, the NHC said. Onshore areas along the coast also account for about 45 percent of USA refining capacity and 51 percent of gas processing.
New Orleans urged residents and businesses to "get prepared and stay informed" about the storm.
Those who wish to courageous the conditions and head to the beach should be extra cautious as strong breezes will produce above-normal tides waves ranging from 2 to 4 feet producing unsafe rip currents through midweek, forecasters said.
Hurricane season doesn't officially begin until June 1, but Alberto apparently missed the memo.
Water vapor imagery and visible satellite imagery over the past six hours shows dry air swirling into the storm.
MIAMI (AP) - U.S. government forecasters are expecting an active Atlantic hurricane season.
This would mean the storm would become more compact around its centre, with the strongest winds and rain located here.