Morning storms, with possible flash flooding, to trigger dramatic temperature drop

The high heat and humidity that has gripped Long Island for three days is predicted to end with storms that could continue to roll through the region Thursday and possibly Friday, the National Weather Service said, dropping the temperature more than 20 degrees in some areas.

"An axis of repetitive torrential rainfall and embedded thunderstorms is likely"  Thursday afternoon and evening, "but it is uncertain on exactly where this develops and how long it lingers over the local area," the weather service said.

Showers fell on some parts of Long Island Wednesday evening. But the game-changing storms Thursday could produce heavy rain at times, and the weather service said Wednesday, "A slow moving frontal system will bring potential for scattered to numerous instances of flash flooding, particularly for the NYC/NJ metro and immediate surroundings" Thursday afternoon into the night.

It added: "Localized severe flooding is possible in this area," referring to western Long Island, with rainfall rates of 2 to 3 inches per house. More isolated and scattered instances of flooding were predicted for eastern Long Island.

"A widespread area of moderate rain will linger across the area on Friday, which could cause lingering flooding issues," the weather service said.

Wednesday, heat index values — what temperatures feel like — reached as high as 102 across Long Island. The weather service issued a heat advisory until 8 p.m. Wednesday and an an air quality alert is in effect until 11 p.m. Wednesday.

"This level of long-duration heat, with little overnight relief, affects anyone without effective cooling and/or adequate hydration," the weather service said in an advisory.

Periods of rain started Wednesday night with storms predicted for Thursday morning that will be shifting weather patterns dramatically, breaking the heat and dropping the temperature about 12 degrees Thursday, despite possible afternoon sunshine.

On Friday, temperatures will drop across the island. Meteorologists forecast the high temperature in Islip will only reach 70, according to Pollina. The coldest high temperature recorded on Aug. 1 at Islip, where NWS records date to 1963, was 68 degrees in 1978.

The chance of rain and thunderstorms will "start to taper off Friday morning" before the island is "completely dry by Friday night." A sunny weekend with temperatures around 80 is predicted. 

Gov. Kathy Hochul said in a release she has directed state agencies to prepare for possible localized flooding. "This is expected to be a slow-moving weather event with the most severe impacts occurring where the storm ultimately sets up," the release said.

“As the forecast shifts from extreme heat to heavy rains, I am urging all New Yorkers to stay vigilant and use caution through the end of this week,” Hochul said.

The rip current risks at South Shore ocean beaches were low Wednesday.