Long Island weather: Heavy rain, thunderstorms could bring flooding Tuesday into Wednesday

A flash flood watch has been extended to western Suffolk County for Tuesday, as multiple rounds of heavy showers and thunderstorms are expected to begin in the afternoon and last through Wednesday night.

The National Weather Service said the timing of the heaviest rain is later than previously thought. In an early morning briefing, the service pushed the area’s flood watch back to 2 p.m. Tuesday and extended its end time to 8 p.m. Wednesday.

"We're looking at most of this rain falling tonight into tomorrow morning," meteorologist Bryan Ramsey said. "That's when you're going to see some of the largest coverage in rainfall and thunderstorms, and where you're going to see some of your highest rainfall rates."

According to an expected rainfall map, the service forecasts northern Long Island to receive more than 2 inches of rain. Parts of southern Long Island and the East End are expected to receive under 2 inches.

Affected areas can expect 1 to 2 inches per hour, but "up to 3 inches can't be ruled out in some isolated areas," Ramsey said. 

New York City and northwestern Nassau County are categorized under a moderate flash flooding risk, and could experience numerous flooding events, while eastern Nassau through western Suffolk fall under a slight flash flooding marginal risk, where scattered flash floods are possible.

The East End is under a marginal risk.

"Minor to isolated moderate flood levels may be exceeded along a few quick responding small rivers, streams, creeks and adjacent roads and properties," the briefing said.

By Wednesday, the system travels northwest, bringing risks of scattered flash floods to Connecticut and the Hudson Valley. Long Island will be under a marginal risk for isolated flash floods.

Ramsey said there is a possibility that the axis of the heaviest rainfall could shift east by Tuesday afternoon. If this were to happen, the service will extend the flood watch into the East End.

"There's still a little bit of variability on exactly where that heaviest rain will fall, but overall, the threat is pretty general across the area," Ramsey said. "So everyone should keep an eye out."

Commuters should stay updated on weather and road conditions and consider working from home on Wednesday. 

"Every flood event we get there are people who will drive through the water think they can make it, and then they're sitting on top of their car waiting to be rescued," Ramsey said. 

While Long Island experienced severe thunderstorms last week, Tuesday night's thunderstorms are categorized as general and widespread. The storms may bring gusts of up to 40 mph, but they will not be nearly as strong or damaging as last week's storm, Ramsey said. 

The metropolitan area and New Jersey are likely to experience damaging gusts of between 60 and 70 mph. 

Before 7 a.m. on Wednesday, Kennedy Airport reported 254 cancellations and 50 delays, on Wednesday, according to the Flight Aware website. LaGuardia Airport reported 17 delays and 213 cancellations.

Gov. Kathy Hochul urged New Yorkers to exercise caution ahead of the storm. If you are in an affected area, have an emergency plan in place, do not touch downed power lines and do not go through floodwaters, Hochul said.

After floodwaters have receded, wait until an area has been declared safe before entering. 

"New York State will be experiencing a prolonged rain event beginning Tuesday that will bring heavy rains and cause flash flooding — New Yorkers should stay vigilant, stay informed, and use caution," Hochul said in a news release on Monday night. "As state agencies are ready and mobilized to keep New Yorkers safe, it is important for everyone to do their part by monitoring your local forecast and when in doubt, turn around, don’t drown."

Check back for updates on this developing story.