A surfer crashes into the water as a subtropical approaches on Monday, May 28, 2018, in Pensacola, Fla. The storm gained the early jump on the 2018 hurricane season as it headed toward anticipated landfall sometime Monday on the northern Gulf Coast, where white sandy beaches emptied of their usual Memorial Day crowds. (AP Photo/Dan Anderson)
A surfer crashes into the water as a subtropical approaches on Monday, May 28, 2018, in Pensacola, Fla. The storm gained the early jump on the 2018 hurricane season as it headed toward anticipated landfall sometime Monday on the northern Gulf Coast, where white sandy beaches emptied of their usual Memorial Day crowds. (AP Photo/Dan Anderson) Credit: Dan Anderson

Subtropical Storm Alberto lumbered ashore Monday on the U.S. Gulf Coast, pelting white sand beaches with blustery winds and stinging rain that kept the usual Memorial Day crowds away.

Forecasters warned heavy rain, flash flooding and dangerous surf posed the biggest threats as Alberto’s ragged core made landfall near Laguna Beach in the Florida Panhandle. A few brief tornadoes also were possible in much of Florida and parts of Georgia, South Carolina and Alabama.

The National Hurricane Center in Miami said at 5 p.m. EDT Monday that Alberto was centered about 15 miles west-northwest of Panama City, Florida. With maximum sustained winds of 45 mph, Alberto was moving north at 9 mph.

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.

Between four and eight inches of rain could pummel Florida Panhandle, eastern and central Alabama, and western Georgia before the storm moves on. Isolated deluges of 12 inches also were possible as the storm heads inland, threatening heavy rains around the Southeast in the coming hours and days.

Lifeguards posted red flags along the white sands of Pensacola Beach, where swimming and wading were banned.