An afternoon deluge flooded Maryland’s biggest beach town and shut down its main highway on a busy weekend for tourists and graduation ceremonies.

More than 7.5 inches of rain fell between noon and 5:30 p.m., said Joe Theobald, director of emergency services for Ocean City. And more rain was forecast to fall. “We’re just trying to get through this and wait for the water to go down,” Theobald said. “The sun will eventually come out again.”

The Ocean City Police Department closed the Coastal Highway north of 94th Street for several hours because high water made the crucial transportation artery impassible. Traffic has been rerouted all the way back to the Delaware state line, Theobald said. The Delaware Department of Transportation also closed State Route 54 where it approaches the beach at Coastal Highway on the Delaware-Maryland state line.

The flooding and closures prompted significant traffic jams on a weekend popular for high school seniors celebrating graduation.

The intense rain came from a series of what’s known as “training thunderstorms,” storms that form and then reform again without moving on to a new area, said Mike Rusnak, a meteorologist with the National Weather Service. “They kept just redeveloping and dumping rain in the same area,” he said.

Rusnak said radar and rain gauges show that as much as 7.5 inches fell within six hours in an 8-mile band between Ocean City and the Delaware state line.

Carmella Jacobs said she was walking into her shift at the Hair Cuttery on 97th Street and Coastal Highway when the rain started. “It was just a torrential downpour,” she said. “People were running off the beach and everything because no one saw it coming. It’s not like there was thunder. It was like the sun was out, and the next thing you know, it’s a flood.”

Jacobs said at the height of the flooding, the water was about 2 feet high on Coastal Highway, covering the wheel wells of sedans and dislodging the wooden beams that rim the shop’s parking lot.

Theobald, the emergency services director, said that the entire city was flooding, but the worst of it was on the north end of town. By 10 p.m., he said, the flood waters had receded and “everything is back to normal.”

Ocean City Mayor Rick Meehan, who was out of town when the storm hit, said that the city was having to tow stranded cars.

Doris Glanden joked that she feels like she needs one. She stopped in the Hair Cuttery to get her hair done before her niece’s graduation, but the flash flood left her stranded in the salon for hours.

Glanden said her husband tried to come pick her up but was stopped by police because of the high water, and she could see him waiting for her on the other side of the flooded Coastal Highway. “I’m trying to figure out if I can cross the street without getting wet because I did just get my hair done,” Glanden said. “I still have to go get dressed, but I’m sure my husband’s furious. I can see my husband from here. This is really an adventure.”

The Associated Press contributed to this article.