The National Hurricane Center track has shifted about 30 miles closer to the Gulf coast and Tropical Storm Warnings have been extended up the coast.
The slow-moving storm is expected to slam the Gulf Coast over the holiday weekend with heavy downpours of 10 to 15 inches in parts of Florida, Louisiana, Mississippi, Alabama and Tennessee. The season is likely to be "near or above normal", according to the hurricane center.
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.
The National Weather Service said: "Swells from Alberto will create risky surf and rip currents along the Gulf Coast".
An official from the National Weather Service warns that even after Subtropical Storm Alberto passes, there's still a risk for rip currents.
Subtropical Storm Alberto heads to the US Gulf
Winds from the storm are forecast to hit Florida's Panhandle on Sunday night. The NWS said a flash flood watch would be in effect from Saturday evening through Tuesday evening for southeastern MS, much of southern Alabama, and the western Florida Panhandle.
"This system will bring excessive rainfall to the watch area beginning Saturday evening and continuing through Tuesday evening".
Forecasters say 2 inches (5 centimeters) of rain is expected on saturated ground with isolated areas getting up to 4 inches (10 centimeters) of rain.
A subtropical storm like Alberto has a less defined and cooler center than a tropical storm, and its strongest winds are found farther from its center.
A tropical storm watch is in effect for parts of MS and Alabama, meaning the conditions for a full storm are possible in the next 48 hours. Subtropical storms can develop into tropical storms, which in turn can strengthen into hurricanes. A tropical storm watch and flash flood watch remain in effect. In Cancun, local newspapers showed scenes of some streets flooded to mid-hubcap level. The main threat is from heavy rain that could lead to flooding, the city said, but also high winds and storm surge could cause problems. Some beachfront and riverfront communities are already handing out sandbags. Tropical downpours will move northward into NCFL starting on Sunday.