New York and New Jersey hit by torrential rain and flash floods, forcing highway closures, suspending subway lines and flight delays.

More than 50 million Americans throughout the Northeast are under flood watches on Monday, with a significant risk of flash flooding in some areas. Flash flood warnings have been issued for cities including New York City, Newark, New Jersey, and Arlington, Virginia -- including the Reagan National Airport -- through Monday evening.

New Yorkers in basement apartments were told to be ready to leave and New Jersey’s governor declared a state of emergency after heavy rains in the northeast caused flash flooding, officials said