Long Island weather: Flash flooding possible Thursday night for Nassau, western Suffolk with wet weekend in store

The National Weather Service has issued a flood watch for Long Island, with heavy rain and thunderstorms expected Thursday afternoon and flash flooding possible into the overnight hours.

In a Thursday afternoon advisory, the weather service said a flood watch was in effect for Nassau and western Suffolk from 2 p.m. Thursday until 2 a.m. Friday.

"Scattered to numerous instances of flash flooding of urban, poor drainage, and low-lying areas, as well as along quick responding rivers, streams and creeks possible. The flooding could be locally significant, causing scattered disruptions to transportation," the weather service said.

"The greatest threat of flash flooding is between 6 p.m. and midnight, potentially lasting a few hours longer for Nassau and western Suffolk Counties," the advisory said of Thursday.

For western Long Island, damaging wind gusts are possible, along with an "isolated" tornado Thursday evening, the weather service said.

The weather service said peak hourly rainfall amounts could be about 2 inches as showers and potential thunderstorms move through the area. Higher amounts were possible in some areas.

Forecasters said the system will be moving into the area by early afternoon Thursday, bringing rain into the early evening.

There's a 40% chance of rain during the day Friday and by evening, a 70% chance of rain that will last through Saturday. Sunday will bring a 40% chance of rain.

Temperatures are expected to hover in the low 80s Thursday and in the high 70s to low 80s Friday, Saturday and Sunday, with overnight lows in the upper 60s, the weather service said.

The rip current risks are currently low at all South Shore beaches from Queens to Montauk, according to the weather service.

By John Valenti

john.valenti@newsday.com

John Valenti, a Newsday reporter since 1981, has been honored nationally by the Associated Press, Society of the Silurians and National Headliner Awards for investigative, enterprise and breaking news reporting, as well as column writing. He is the author of “Swee'pea,” about New York playground basketball star Lloyd Daniels. His debut crime novel, “For Nothing Is Hidden,” rooted in 1950s Long Island, was released in October 2025.