The heaviest rand and strongest winds began to hit Panama City Beach at around 10am on Monday (4pm BST) and the conditions will continue into the afternoon as the centre of the storm gets closer to land. The Florida panhandle, a good portion of Alabama and western Georgia are dramatically more at risk for flash flooding with this storm.
Alberto's top winds rose to 50 miles (80 kilometers) per hour early Sunday, up from 40 earlier, the National Hurricane Center said in a 11 a.m.
"We are under this tropical-like influence and that is not going to really breakdown this pattern for at least the better part of this week, " said Al Moore, a meteorologist with the National Weather Service in Columbia.
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 storm is moving north to the coast at about 8 miles per hour and is expected to move faster as it heads north over the next few days.
A storm surge watch remains in effect for much of northern Florida, from the Suwannee to Navarre in the Panhandle.
It will bring heavy rain and winds of 80km/h (50mph) across southern states, the US National Hurricane Center said.
Also any showers or storms that pop up due to the daytime heating will be moving in the flow around Alberto and will travel north to south.
The storm is the first storm of this year's hurricane season, coming a few day before the season officially starts on June 1.
A view of a partially flooded farm as Subtropical Storm Alberto passes by the west coast of Cuba, in Bahia Honda, Cuba, May 26, 2018. But the storm still poses a considerable threat to the Florida Panhandle as it is predicted to move ashore there on Monday.
Tropical Storm warnings on the Gulf Coast have been called off south of the Anclote River, however, they are still in effect for the Anclote River to the Mississippi/Alabama border. "So how often can you say you rode a storm out?"
Rough conditions were whipping up big waves off the eastern and northern Gulf Coast, and authorities warned swimmers to stay out of the surf because of life-threatening swells and rip currents. The tropical system became a subtropical storm Friday, the National Hurricane Center said. Overnight lows will be in the low 70s.
The National Weather Service has issued a flash flood watch for an area stretching from MS to North Carolina that is home to millions of people.
As several states in the Southeast declare emergencies ahead of Subtropical Storm Alberto, forecasters in Upstate New York are tracking its progress northward.