Torrential rain swept through southeastern Connecticut Wednesday afternoon, sparking a flash flood warning and at least a dozen road closures in the area.

Gary Lessor, a meteorologist and assistant director with The Weather Center at Western Connecticut State University in Danbury, said a third of an inch of rain dumped on the Groton-New London area in just one hour.

"Some places had a month's worth of rainfall in the past 24 hours," Lessor said, citing about 3.6 inches falling in Waterford, 2.39 in New London and 1.53 in Lisbon, with the heaviest coming between 2 and 3 p.m. Wednesday.

Social media posts showed trucks and cars splashing through roads in Waterford, Niantic and New London. In Groton, afternoon school buses were delayed about 15 minutes due to road conditions and flooding in the region.

"With these torrential downpours, it doesn't take much" for flash flooding to start, Lessor said. "You see dead leaves coming off trees and other stuff coming off vegetation, blocking drainage."

The National Weather Service issued a flash flood warning shortly after 2 p.m., with Doppler radar showing thunderstorms producing heavy rain across New London, Norwich, Groton, Mystic, Waterford, East Lyme, Ledyard, Griswold, Preston, Bozrah, Voluntown, Gales Ferry, Montville and North Stonington.

The warning was in effect until 4:15 p.m.

Lessor said a stationary front draped across the northeast, triggering showers and thunderstorms in the region. The temperature and dew point remained in the low 70s throughout the day, with high humidity and instability combining to make the region's air mass on par with Florida or Bermuda, Lessor said.

"So, you get these heavy downpours," he said, noting the pelting of afternoon rain had "absolutely no relation to Hurricane Florence. Even Florence isn't bringing rain to the Carolinas yet."

Public works and emergency management teams grappled with flooded roads throughout the region.

In New London, police Officer Todd Lynch said several roads temporarily were closed, including Broad Street at Ledyard Street; Bank Street between Howard Street and Tilley Street; Bank Street at Truman Street, Montauk Avenue and Shaw Street; Pequot Avenue at Greens Harbor Beach; Shaw Street at Robinson Street, and Garfield Avenue at Elm Street.

Chief Administrative Officer Steve Fields said crews from public works and the fire department are on hand to help pump water and direct traffic where needed. Public works crews also were working to fix one of two drainage pumps on Bank Street that failed.

Water Street, near the city-owned parking garage, also had flooded at one point Wednesday afternoon. It was back open as of 3 p.m.

Sgt. Chris Merrill of the Norwich Police Department said the only closure in his city was Otis Street, due to a downed tree.

"We have a lot of standing water on a lot of the streets due to the heavy rain volume," he added. "We just want to caution the public to keep an eye out for standing water on the roadways."

At around 8 p.m., a tree fell on a garage on Doyle Road in Waterford. No injuries were reported, police said.

In Niantic, police Chief Mike Finkelstein said Main Street at Pennsylvania Avenue temporarily had been closed due to flooding. Other roads had been hit with heavy rain but remained passable, he said. Finkelstein noted police and the state Department of Transportation were working to remediate impacted areas.

Waterford police said flash flooding occurred in several areas, including on Route 85, Route 156 and Route 1.

Ledyard police said Tanager Lane temporarily was closed about 3 p.m.

The region saw scattered power outages throughout the evening, according to the utility Eversource's website.

Day Staff Writers Greg Smith and Martha Shanahan contributed to this report.

b.kail@theday.com