Millions of residents across New York City, Long Island, the Hudson Valley, northern New Jersey, and Connecticut remain under a Flash Flood Watch as a slow-moving storm system brings repeated rounds of torrential rain, dangerous flash flooding, and strong thunderstorms through Monday night.

The National Weather Service warned that rainfall rates could exceed two inches per hour, with isolated locations receiving as much as six inches of rain before the storm exits the region. Because many of the storms are expected to move repeatedly over the same areas, forecasters say flash flooding can develop rapidly, even outside traditionally flood-prone locations.

New York City Mayor Zohran Mamdani activated the City’s Flash Flood Emergency Plan on Sunday night, mobilizing agencies across the five boroughs ahead of the storm.

“City workers are doing everything possible to prepare for this storm — clearing catch basins, inspecting flood-prone neighborhoods, reaching out to New Yorkers living in basement apartments and positioning emergency response teams across the five boroughs,” Mamdani said.

He urged residents to remain vigilant, adding: “Now it’s time for all of us to do our part. Limit travel if you can, plan for delays and take these warnings seriously. If heavy rain begins, if the winds pick up or if you hear thunder — get inside and wait out the dangerous conditions.”

The city’s Department of Environmental Protection, Department of Sanitation, and Department of Transportation spent the weekend clearing storm drains and catch basins while specialized emergency crews and equipment were pre-positioned throughout the city in anticipation of flooding.

Officials are also encouraging New Yorkers to check on neighbors—particularly those living in basement apartments, which are especially vulnerable to rapidly rising floodwaters.

Although the greatest flash flood threat shifted overnight toward Long Island and Connecticut, meteorologists stress that New York City and northern New Jersey remain at risk. Any location across the Tri-State area could experience localized rainfall exceeding two inches per hour, overwhelming drainage systems and flooding roads, highways, subway stations, and low-lying neighborhoods.

The storm follows several days of extreme heat and powerful thunderstorms that swept through the region over the Independence Day weekend. Some of those storms produced hurricane-force wind gusts on Long Island, toppling trees and leaving debris that could further clog drainage systems during the current deluge.

Transportation disruptions are already mounting across the region.

As of Monday morning, Newark Liberty International Airport reported 47 flight delays and 53 cancellations. LaGuardia Airport had 59 delays and 124 cancellations, while John F. Kennedy International Airport reported 97 delays and 74 cancellations.

Transit agencies are also warning of delays. NJ Transit has already reported weather-related impacts, while the Metropolitan Transportation Authority said the New York City subway system can generally handle rainfall rates of up to 1.75 inches per hour. Rainfall exceeding two inches per hour could overwhelm parts of the system and lead to flooding in stations and tunnels.

Forecasters expect periods of heavy rain to continue through Monday night before the storm gradually moves south. Wet conditions may linger into Tuesday morning before drier weather arrives. Wednesday is expected to bring partial sunshine and temperatures in the low 80s, although heat and humidity are forecast to build again later in the week with another chance of thunderstorms by Friday and Saturday.

Officials continue to urge residents to avoid driving through flooded roadways, never enter floodwaters on foot, monitor weather alerts, and expect significant travel delays throughout the day.

(YWN World Headquarters – NYC)