WAVELAND, Miss. — Hurricane Sally, one of four storms churning simultaneously in the Atlantic, closed in on the Gulf Coast on Monday with rapidly strengthening winds of at least 100 mph and the potential for up to 2 feet of rain that could bring severe flooding.

The storm was on a track to brush by the southeastern tip of Louisiana and then blow ashore late Tuesday or early Wednesday near the Mississippi-Alabama state line.

Storm-weary Gulf Coast residents rushed to buy bottled water and other supplies ahead of the hurricane, which powered up to a Category 2 in the afternoon. Forecasters said sustained winds could reach 110 mph by landfall.

“This is the real deal, and it deserves your attention,” Mississippi Gov. Tate Reeves wrote on Twitter, shortly after the storm was upgraded. He urged people in low-lying areas to prepare to evacuate. “Be smart. Prepare for worst. Pray for the best,” he said.

Seawater and sand swept onto roads on one end of Dauphin Island off the coast of Alabama, washing away several cars, Dauphin Island Mayor Jeff Collier said. He said about a dozen people had to be evacuated by Humvee.

To the west, in Mississippi, Jeremy Burke lifted things off the floor in case of flooding in his Bay Books bookstore in the Old Town neighborhood of Bay St. Louis, a popular weekend getaway from New Orleans, about 60 miles to the west.

“It’s turning into a ghost town,” he said.

Sally has lots of company during what has become one of the busiest hurricane seasons in history — so busy that forecasters have almost run through the alphabet of names with 2½ months still to go.

For only the second time on record, forecasters said, five tropical cyclones swirled simultaneously in the Atlantic basin at one point Monday. The last time that happened was in 1971.

In addition to Sally were Hurricane Paulette, which passed over a well-fortified Bermuda on Monday and was expected to peel harmlessly out into the North Atlantic; and Tropical Storms Rene, Teddy and Vicky, all of them out at sea and unlikely to threaten land this week, if at all. Rene was downgraded to a trough of low pressure Monday evening.

As of late afternoon, Sally was about 145 miles (southeast of Biloxi, Miss., moving at 6 mph.

The storm’s forecast track was nudged east Monday afternoon but much of southeast Louisiana remained under a hurricane warning. Storm surge warnings stretched from Port Fourchon in Louisiana to the line between Okaloosa and Walton counties in Florida. People in New Orleans watched the storm’s track intently, worried that Sally would pose the latest test for pumps used in the low-lying city’s century-old drainage system.

In eastern New Orleans, drainage canals were lowered in anticipation of torrential rains. New Orleans police went on 12-hour shifts, and rescue boats, barricades, backup generators and other equipment were readied.