Flash flooding impacts New York City transportation as storms hit the Northeast

More than 50 million Americans throughout the Northeast are under flood watches.

More than 50 million Americans throughout the Northeast are under flood watches on Monday, with flash flooding causing significant delays to New York City transportation.

Flash flood warnings have been issued for cities including New York City, Washington, D.C., Baltimore, Newark, New Jersey, and Arlington, Virginia -- including the Reagan National Airport -- through Monday evening.

Life-threatening flooding was possible in western Union County, New Jersey, the National Weather Service warned.

Video from Manhattan on Monday evening showed flood waters rushing into the 28th Street subway station as passengers were aboard a train.

NYPD Transportation released a statement on X saying flooding conditions on the Cross Bronx Expressway at Jerome Avenue was blocked in both directions. "Consider alternate routes and expect delays," the agency said.

Additionally, Bergen County in northeastern New Jersey and Westchester County in New York are also under a flash flood warning.

Travelers across the country continue to face travel disruptions with 1,966 flights cancelled and more than 10,090 delayed nationwide due to weather, with the East Coast is seeing the biggest impacts due to the storms.

United Airlines, which has a hub at Newark Liberty International Airport in New Jersey and is experiencing these delays said in a statement on Monday, "Severe weather conditions are impacting operations at Newark Liberty with a ground stop issued to manage volume and limit congestion."

New Jersey Gov. Phil Murphy declared a state of emergency due to the flash flooding and "high levels of rainfall in parts of the state."

"Please stay indoors and avoid unnecessary travel," he said on X.

Slow-moving storms are expected to drop a lot of rain quickly. Rainfall rates up to 3 to 4 inches per hour are possible.

Up to 5 inches of rain has already fallen in parts of northern and central Jersey.

Vehicles stranded due to flash flooding have been reported in areas including Union County, New Jersey, and Westchester County.

Widespread flash flooding was also reported in Lancaster County in southern Pennsylvania after heavy rain moved through the area earlier Monday.

This is a developing story. Please check back for updates.