Subtropical Storm Alberto has formed over the northwestern Caribbean Sea, forecasters with the National Hurricane Center said Friday.

Alberto had maximum sustained winds of 40 mph and was about 55 miles south of Cozumel, Mexico, moving north-northeast at 6 mph, according to the 11 a.m. advisory from the NHC.

The storm is expected to bring wet weather to South Florida through the Memorial Day weekend. The system is expected to stay to the west of South Florida as it moves through the Gulf of Mexico.

Rainfall accmumulations of 4 to 8 inches with maximum amounts of 12 inches are possible across the Florida Keys and southern and southwestern Florida, according to the NHC.

A tropical storm watch was in effect for the east coast of the Yucatan Peninsula from Tulum to Cabo Catoche and for the Cuban province of Pinar del Rio.

Portions of the northern Gulf Coast are likely to experience tropical storm force winds and storm surge. An Air Force Reserve reconnaissance aircraft is scheduled to investigate the weather system Friday.

The tropical threat comes earlier than usual. The six-month hurricane season doesn't begin until June 1.