Scattered thunderstorms are expected Monday afternoon through early evening, with "isolated strong to severe" storms possible, the National Weather Service said.
The main threats with these storms are damaging winds, small hail and heavy rain that may lead to flooding, forecasters said.
Most of this week is expected to offer Long Islanders steady summer weather, with high temperatures threatening to reach 90 degrees as it did Monday, according to the National Weather Service.
The thermometer hit 90 degrees at 2:36 p.m. at Long Island MacArthur Airport, according to the weather service.
The state Department of Environmental Conservation issued an ozone advisory for New York City and surrounding areas, including Long Island, until 11 p.m. Monday. The advisory warns that summer heat can elevate ground level ozone, a major component of smog. People, especially children and those who exercise or work outdoors, should consider limiting strenuous physical activity. Also particularly vulnerable are people with respiratory diseases, the agency said.
The prediction is for warm, humid days with some relief, temperature-wise, at night, when the thermometer dips to the high 60s and low 70s, David Stark, a meteorologist with the Upton-based service, said Monday.
A ridge of high pressure is creating the heat, Stark said. For at least until late Thursday, that heat -- which is originating from states south and southwest -- should dominate.
There's a slight chance of temperatures reaching 90 or higher through Wednesday, Stark said, but it's unlikely, because of the ocean-based wind factor.
The record high for Monday is 93 in 2010, Stark said. The record high for Tuesday and Wednesday is 92 each day, according to service statistics.
Between Monday and Wednesday, there is a 20 percent to 30 percent chance of rain, the service said.
Hempstead Supervisor Kate Murray announced that through Wednesday the town is extending hours at its eight pools and seven beaches, and 15 cooling centers will be open from 9 a.m. to 8 p.m.
By late Thursday, the chance for rain increases as a cold front pushes in from Canada and the Great Lakes, Stark said.
Thursday's forecast calls for slightly cooler high temperatures, in the high 70s to low 80s, and the chance of precipitation increases to 40 percent. By the weekend, it's 50 percent.
"The low-pressure system later in the week should provide some cloud cover, too," Stark said.
The result most likely is a cooler, wetter weekend.