PROJECT ALERT NOTICE (NY) Catastrophic Flash flooding in New York

Date: Thu, 02 Sep 2021 10:51:58 EDT

Summary: Catastrophic flash flooding in New York City and southeastern NY from the remnants of Tropical Storm Ida.

Catastrophic flash flooding occurred in New York City and southeastern NY last night and this morning (September 1-2) as a result of record and torrential rainfall from the remnants of Tropical Storm Ida interacting with a stalled frontal system. A total of 4-9 inches of rainfall and rainfall rates up to 3-4 inches/hr on soils previously saturated by several inches of rain from Hurricane Henri resulted in a Flash Flood Emergency being issued by the NWS and a State of Emergency declared by the Governor. There have been reported fatalities; the New York City subway service suspended; widespread flooded roadways, basements, and buildings; stranded vehicles; and evacuations.

The USGS streamgage Hackensack River at West Nyack, NY (1958-current) recorded a provisional peak of 11.5 ft that matched the record peak during Hurricane Irene in 2011. Several USGS streamgages exceeded NWS Flood stages: Bronx R at Bronx, NY (Major flood stage), Mahwah R at Suffern, NY (Moderate flood stage), and Wappingers Creek and Rondout Creek (Minor flood stage). A total of 9 USGS crews (18 personnel) from the Milford, Troy, Coram, and Cortland offices are making high-flow discharge measurements today for rating calibration. All USGS gages are currently operating.