Drenching rain led to flash floods in the Washington and Baltimore metro areas Tuesday as a potent storm system slogged through the Mid-Atlantic.
The heavy rain is forecast to pelt the Northeast and New England later on Tuesday and into Wednesday.
A flash flood emergency was in effect for parts of the Baltimore area as of late afternoon.
Several people were rescued from flooded cars and numerous roads were closed in the D.C. area, WUSA-TV reported. Roads are also closed in the Baltimore area.
As of late afternoon, Baltimore had picked up 6.27 inches of rain, making this the city's second-rainiest August day since records began in 1871. Photos on social media showed cars swamped in a parking lot at BWI airport.
Some spots had picked up an estimated 10 inches of rain, the National Weather Service reported. "Numerous water rescues and road closures have been reported."
Further north, "rainfall rates of 1 to 2 inches per hour are likely during the periods of heaviest rain," according to an online forecast from the weather service in New York City. "Widespread rainfall amounts of 2 to 3 inches and locally over 4 inches are possible."
Rainfall of this intensity and magnitude could cause significant urban and poor drainage flooding, the weather service warned. Flooding of small streams is also possible.
The National Weather Service has placed parts of the region under a flash flood watch. This includes the entire New York City metro area and most of southern New England.
"High moisture content in the atmosphere will heighten the risk for torrential downpours that could lead to flash flooding," said AccuWeather meteorologist Sarah Glenn.
"The evening commute on Tuesday will be very slow from New York City to Philadelphia," reports AccuWeather meteorologist Brian Edwards. "Some commuters may even face detours around any localized flooding problems that develop."
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Other cities at risk for flooding through Wednesday include Albany, Boston, Burlington, Vt., and Portland, Maine.
Delta Air Lines, Jet Blue and United are waiving change fees for flights in the mid-Atlantic and New York City due to the foul weather.
Severe thunderstorms could also rattle portions of eastern Ohio, western Pennsylvania, West Virginia, Maryland, Virginia and Delaware on Tuesday, the Storm Prediction Center forecasts. The main threats will be damaging wind gusts and large hail.
In the Southwest, an increase in monsoonal moisture will bring scattered to numerous showers and thunderstorms across the Four Corners states the next few days, the weather service predicts.