The heavy rainfall poses a significant risk of flash flooding, particularly in low-lying areas, streets, and basements. Travel conditions are expected to be hazardous, with hundreds of flights already canceled across New York area airports, including 117 at JFK, 109 at LaGuardia, and 61 at Newark. Counties in New York, New Jersey, and Connecticut are under Flood Watch, with areas like Nassau, Westchester, and Bergen among those affected. Residents are urged to remain vigilant as isolated severe thunderstorms could exacerbate flooding risks.