Flash flood warnings for parts of Long Island, with up to 4 inches of rain expected

The National Weather Service has extended a flash flood warning until 3:30 p.m. for western Suffolk County due to heavy rain and thunderstorms moving through some areas.

A flood watch was issued for the entire region through Monday night, with multiple rounds of storms expected, the weather service said. 

"It looks like the rainfall is going to surge this afternoon," weather service meteorologist Bryan Greenblatt said. "The southern and southeastern part of Long Island is at most risk, but could move eastward." He said "the greatest window" for heavy rain is Monday afternoon until between 6 and 7 p.m.

Rain is expected to lighten up overnight and the flood threat is expected to diminish to light rain through Tuesday, Greenblatt said.

Between 2 and 4 inches of rain were expected across parts of Long Island through Tuesday, prompting Nassau and Suffolk counties to declare states of emergency and call on residents to avoid unnecessary travel. 

In some places, there could be2 inches of rain per hour, which could cause flash flooding.

"Conditions remain favorable for torrential rainfall rates/flooding today due to a humid air mass over the region," a 3 p.m. advisory from the weather service said.

The heavy rain followed a weekend storm that hit Suffolk County hard, toppling hundreds of trees, knocking down power lines and leaving thousands waiting Sunday night for electricity to be restored. PSEG Long Island reported more than 3,000 customers out of power as of 12:28 p.m.

Suffolk County Executive Edward P. Romaine said a state of emergency for the county will continue for 30 days.

In Nassau, which avoided the worst of the weekend storm, County Executive Bruce Blakeman declared a state of emergency from 6 p.m. on Sunday through Tuesday at 6 a.m. due to "the likelihood of extreme precipitation and potential flooding and downed trees."

"At this time," Blakeman said in a statement, "no mandatory evacuation is required; however, we will closely monitor the situation."

Separately, Hempstead Town Supervisor John Ferretti declared a state of emergency for the town through 6 a.m. Tuesday. "All clinics, outdoor lessons, outdoor recreation classes, and swimming lessons are canceled" Monday, Ferretti said in a statement.

Gov. Kathy Hochul's Office also urged New Yorkers to use caution "due to the potential for flash flooding."

The summer storms come after an oppressive heat wave swept through the central and eastern United States, making for an enthusiastic, but slightly wilted, Fourth of July weekend. The temperature just missed the record high for Independence Day on Long Island, which was 97 degrees in 2010.