Strong rain storms lashed the U.S. East Coast Thursday, delaying flights and prompting emergency rescues of motorists trapped in deep water on busy highways from the Philadelphia area to New York City.

Most of the rain is forecast to fall in as little as 3-6 hours. A small chance of heavier rain and flooding could pose "an elevated threat to life and cause significant disruptions to transportation, flood underground infrastructure and basements and first floors of residences and businesses," with water rescues needed, the weather service said.