Portland obliterated its previous rainfall record for Wednesday’s date, with an official 6.44 inches falling at Portland International Jetport as thunderstorms flooded streets throughout southern Maine and knocked out power to thousands.

The previous city record for Aug. 13 was 2.38 inches, set in 2004, according to the National Weather Service.

Unofficial radar estimates near the Jetport showed that more than 8 inches fell, according to the National Weather Service.

Flood waters had receded in Portland by 7:30 a.m. Thursday and road crews were replacing manhole covers that had been dislodged by the torrential rains. Police were working with tow truck operators to remove cars that were stranded during the height of Wednesday night’s storm.

More than 6,000 Central Maine Power Co. customers were without power late Wednesday night. By 6:15 a.m. Thursday, more than 4,500 CMP customers were still without power, mostly in Lincoln County. Emera Maine reported more than 3,300 outages, mostly in Penobscot County.

More than 4 inches of rain fell between 9 and 11 p.m. in Portland, the weather service reported late Wednesday night. Margaret Curtis, a meteorologist with the National Weather Service in Gray, said 1.42 inches fell on the Portland International Jetport in just 30 minutes.

The effects of the drenching storm were felt throughout southern Maine, with flooded roads closed and motorists stranded. Fire and Police Departments received dozens of calls for help from motorists and residents with flooded basements.

The Portland Fire Department issued a warning late Wednesday for motorists to drive with caution because the flooding had washed away manhole covers, creating “deep potholes” on city streets. In Scarborough, Route 1 was closed shortly before midnight because of flooding. When it would reopen was unclear because an astronomical high tide was expected at 2 a.m.

The National Weather Service had issued flash flood and severe storm warnings for the Portland and Brunswick areas, effective until just before midnight Wednesday. “This is a particularly dangerous and life threatening situation, stay off the roads and do not drive,” the warning said.

The rain came from a low-pressure storm system moving in from the south along the coast, an unusually strong one for this time of year. Such storms are more common in the spring and fall than in summer, according to the National Weather Service.

The town of Scarborough was particularly hard hit and the Nonesuch River reached flood stage. Sgt. Steven Thibodeau said police had to shut down Route 114 after the river flowed over its banks.

“Where isn’t there flooding?” Thibodeau asked. “An officer just came in off the street and said it was raining so hard it was like blizzard conditions. You couldn’t see the car in front of you.”

Thibodeau said a car got stuck on Broadturn Road after water flooded the street and a section of the road was closed afterward.

Scarborough police shut down the south and northbound lanes of the section of Route 1 that carries traffic over the Scarborough Marsh early Thursday morning.

In Portland, there were dozens of reports of flooded streets and basements. A person who answered the telephone at the Portland police station said emergency communications line had been swamped with calls for assistance.

Attempts to reach police and fire dispatchers were unsuccessful because they were flooded with calls for assistance.

Twitter, the social media outlet, lit up Wednesday night with reports of widespread flooding and photographs.

Several people tweeted photographs of cars floating in water on Park Avenue near the H.P. Hood milk packaging plant in Portland.

There were reports that the La Quinta Inn & Suites on Park Avenue, near a flooded area, had to be evacuated.

A news reporter for WCSH-TV said that Marginal Way in Portland was flooded, and cautioned motorists against using the road.

“Turn around. Don’t drown,” the weather service’s Curtis said, giving advice to drivers who were out on the roads at the time. “It can be really hard to tell how deep a puddle is.”

In South Portland, the fire department responded to more than 60 calls for help – the department averages nine calls a day – and had to rescue six motorists who became stranded in their vehicles after roads flooded, according to Lt. Robb Couture of the South Portland Fire Department.

Fire crews were called late Wednesday night to 38 Jefferson St. in South Portland where residents reported their foundation had buckled because of a flooded basement. A section of Broadway in the Thornton Heights neighborhood had to be closed after it flooded.

“Every vehicle and person we have is on a call right now,” Couture said Wednesday night.

In Falmouth, police closed a section of Allen Avenue, near the Presumpscot River bridge, after it flooded, Fire Chief Howard Rice said.

“We’ve got water over several roads tonight,” Rice said.

The rain was expected to clear out early Thursday and become partly sunny by about 9 a.m., according to the weather service. The rest of the day should be mostly sunny, with the possibility of a shower in the mountains.