Flash Flood — Nassau, New York

2023-09-29 · near North Vly Stream, Nassau, New York

Event narrative

Hempstead Turnpike closed in both directions between Holland and Plainfield Ave. All lanes are blocked due to flooding.

Wider weather episode

An inverted trough extending from a low pressure system over the Western Atlantic provided a focus for persistent heavy convective rain to continually develop over the NYC metro and surrounding areas during much of the day on September 29th, 2023. In an environment with anomalously high moisture given the time of year, PWATs near 1.5-1.7 inches, rounds of heavy rainfall fell over the same areas for more than 12-18 hours. While the rainfall rates were generally 1 inch per hour or less, the persistence in the heavier rainfall resulted in a widespread total of 4-6 inches of rain with JFK receiving almost 9 inches of rain from the event. There were some brief periods of time where rainfall rates peaked at near 2 inches per hour. This resulted in widespread flash flooding across Southeast NY and Southern Connecticut.

View location on OpenStreetMap → (40.7100, -73.7100)

Source: NOAA Storm Events Database, event_id 1135793. Narrative written by the NWS forecast office that issued the report.