Heavy rain soaks dry region, brings traffic slowdowns

The National Weather Service issued a flood advisory for Boston yesterday in anticipation of heavy downpours and thunderstorms that are expected to continue through today.

As rain fell, areas like Storrow Drive and low overpasses in Boston, Cambridge, and Somerville turned into dangerous makeshift rivers; and drivers were not ready.

An off-duty Somerville firefighter found motorist Christine Broderick on the roof of her submerged vehicle yesterday. She was scared and couldn’t swim as waters rose to about 12 feet, police said.

“I was coming out of the Stop & Shop, and I looked right and saw an extreme amount of water coming out of the manholes,’’ said firefighter Michael Marino in a phone interview from his firehouse last night. “I noticed someone waving their arms. I put on my gear and came running down the embankment to the front of the underpass.’’

“The water was rising pretty good. I jumped in with shorts and a T-shirt, swam over to her, and just let her know that everything was going to be OK.’’

Marino and Stephen Barnes, a state trooper, stayed near her until additional help arrived. Other firefighters threw a life ring into the water, and Marino helped pull Broderick to safety.

In a teary televised interview, Broderick thanked Marino, saying he saved her life.

A State Police dive team searched four other submerged vehicles, fearing people could be trapped, but everyone had escaped safely. Thirteen troopers were taken to a hospital to be decontaminated after raw sewage leaked into the water.

Marino, a Somerville native, has been a firefighter for three years after spending five years as a rescue swimmer in the Navy.

Heavy rains, which began about 2:30 p.m. yesterday and turned lighter by the evening, officially totaled 1.65 inches at Logan International Airport, with amateur spotters reporting 2 inches in Boston and 3.3 inches in Cambridge, according to the National Weather Service in Taunton.

With little rain for more than two weeks, dry soil was unable to soak up the water and threatened to cause run-off, exacerbating flood concerns for communities outside Boston, said Kim Buttrick, a meteorologist with the National Weather Service.

“It’s like being in a city where everything runs off cement,’’ Buttrick said.

Flooding also occurred on Storrow Drive, making it look more like the river it runs next to than a roadway. Storrow Drive had to be closed in both directions at the Harvard and Longfellow bridges. The road had only one passable lane in each direction at 10 p.m.

The Somerville Police Department headquarters had to be closed because of the flooding, according to an e-mail city officials sent to residents.

While heavy rains disrupted traffic, they also were an obstacle for MBTA passengers and officials.

“We actually did have flooding’’ that closed the Downtown Crossing T station at 3 p.m., said Lydia Rivera, a spokeswoman for the MBTA. Service resumed after water receded about a half-hour later, she added.

Train traffic was diverted on the commuter rail and the Red, Orange, and Green lines because of weather-related problems, according to MBTA alerts.

Inbound service for the Fitchburg/South Acton commuter rail was terminated at the Porter Square station because of flooding on the tracks, said Joe Pesaturo, a T spokesman. Even as the tracks reopened last night, trains remained delayed.

Forced to bypass Wollaston station, the Red Line used shuttle buses between the North Quincy and Wollaston stops.

Similarly, the MBTA said, the Orange Line ran shuttle buses between Roxbury Crossing and Ruggles, while the Green Line, in an alert, warned passengers of delays up to 20 minutes because of the weather. Service gradually returned to normal as the waters receded.

One positive aspect to the storms, Buttrick said, was the cooling down of a recent stretch of temperatures above 90 degrees.

However, she said, the relief will not last.

While rain will temporarily cool temperatures, it will only provide a “brief respite from the above 90-degree heat,’’ Buttrick said.

The National Weather Service predicted scattered showers today into tonight. Tomorrow, a sunny day with a high of 86 degrees, is expected.

John M. Guilfoil can be reached at jguilfoil@globe.com; Teehan at steehan@globe.com.