Severe flash flooding across the tri-state area on Monday caused major subway delays and road closures across the Big Apple and pushed New Jersey to declare a state of emergency. All five boroughs and Nassau County were under a flash flood warning through midnight, according to the National Weather Service. Westchester County was placed under the same alert until 12:15 a.m. after the southbound lanes on the Taconic State and Saw Mill River Parkway experienced severe flooding. The 1, 2 and 3 trains were all suspended in Manhattan while the MTA addresses flooding across several stations, the agency said.