A flash flood is a rapid rise of water along a stream or in a low-lying urban area, the National Weather Service said. Flash flooding can result from slow-moving thunderstorms, from numerous thunderstorms that develop repeatedly over the same area, or from heavy rains associated with tropical cyclones.

Flash flood warnings and watches popped up across the New York City area Monday evening, as powerful storms and downpours led to many stalled vehicles and multiple rescues. A flash flood warning was in effect in New York City until 9:45 p.