On September 29, 2023, heavy rainfall led to flooding across portions of the New York metropolitan area and areas in New York City, United States. New York governor Kathy Hochul declared a state of emergency for five boroughs in New York, including portions of Hudson Valley and Long Island, and New York City mayor Eric Adams declared a state of emergency for the city. New Jersey governor Phil Murphy declared a state of emergency for all 21 counties in the state, and Hoboken, New Jersey mayor Ravinder Bhalla also declared a state of emergency.
The flooding suspended train service across numerous lines in Brooklyn, and every line on the New York City Subway was affected. Metro-North Railroad service was suspended on three lines, and several boroughs and numerous streets were flooded throughout the region. A ground stop was imposed on LaGuardia Airport, where nearly 60 flights were cancelled. The heavy rainfall was caused by a stalled low-pressure area as showers and thunderstorms developed on September 29.
Meteorological synopsis
A moderate risk of excessive rainfall was issued by the Weather Prediction Center, and a flood watch was issued for portions of New York, Connecticut, and New Jersey. A weak low-pressure area developed off the East Coast of the United States, absorbed the remains of Tropical Storm Ophelia, then stalled, dropping heavy rainfall across areas that were already under a flood watch after Ophelia had moved through the same region days earlier. Convection developed on the morning of September 29 after an upper-level trough approached from the Ohio valley and interacted with a strengthening cold front offshore in the Atlantic Ocean.
Widespread heavy rainfall occurred in a concentrated area from the New York metropolitan area to southern New York to southern Connecticut to western Massachusetts along a low-level convergence axis. Favorable precipitable water values around 1.6 inches, elevated convective instability, and southeasterly low-level winds between 20-30 knots supported several rounds of heavy rain across the concentrated area. The mesoscale low-pressure area then moved east on the afternoon of September 29, where the convergence axis and elevated instability again produced heavy rainfall across Long Island, and weak instability values in the hundreds and moisture transport also contributed to rainfall rates of per hour across southern Connecticut and western Massachusetts.
Impact
The National Weather Service in New York City issued a considerable flash flood warning for Manhattan, Brooklyn, and Queens as more than of rain fell throughout the region. Flood warnings also covered more than 18 million people across the New York metropolitan area.
New York governor Kathy Hochul declared a state of emergency for five boroughs in New York, including boroughs in Hudson Valley and Long Island, and New York City mayor Eric Adams declared a state of emergency for the city. The New York Army National Guard was deployed. Several highways, including portions of FDR Drive, Hutchinson River Parkway, Major Deegan Expressway (I-87), Cross Island Parkway and Grand Central Parkway, were closed. Traffic was stopped on the Prospect Expressway (NY 27) near Kensington as vehicles were inundated by floodwaters.
Every line on the New York City Subway was affected, with four routes completely suspended, 12 partially suspended, and an additional eight services significantly delayed, which included no train service on the 2, 3, 4, 5 routes in Brooklyn, and no service on the B and G routes at all. Metro-North Railroad service was suspended on the New Haven, Hudson and Harlem lines, and a terminal at LaGuardia Airport was shut down due to flooding. A ground stop was also imposed at the airport. Departures were delayed at John F. Kennedy International Airport due to heavy rainfall, with total rainfall of . Of that total, of rain fell there on just September 29, setting the preliminary record for the highest rainfall in one day. NYC Ferry and Amtrak service was also delayed.