An excessive heat warning will begin Sunday morning for northern Nassau County, with a lower-level heat advisory for the rest of Long Island, forecasters say.
The warning, which is for Nassau County north of the Long Island Expressway, is scheduled to go from 6 a.m. Sunday to 6 a.m. Monday, according to Joe Pollina, a meteorologist in the National Weather Service’s Upton office.
The heat advisory, meanwhile, runs from 6 a.m. Sunday to 9 a.m. Monday, Pollina said. A heat advisory is issued when the combined heat and humidity is expected to make it feel like 95 to 99 degrees two or more days in a row, or when it’s expected to feel like 100 to 104 degrees for any length of time.
There is also an air quality alert in place — meaning there will be elevated levels of ozone — Sunday from 11 a.m. to 11 p.m., Pollina said. Ozone levels are often elevated after noon through early evening on hot, sunny days.
Sunday’s highs are expected to be in the lower to mid-90s for most of Long Island, Pollina said, but the upper 90s for western Nassau County. The record high in Islip for Sunday is 96 degrees and the forecast is for a high of 94. A normal temperature is 81 degrees there for this time of year.
Suffolk County Health Commissioner Dr. James Tomarken advises that “all residents, especially young children, seniors, those who exercise or are involved in strenuous outdoor work, and those with pre-existing respiratory or heart problems, limit strenuous outdoor activity.”
Monday will bring slight relief from the excessive heat. Pollina said temperatures are predicted to be “a little cooler” – mid- to upper 80s for most of the Island, close to 90 degrees for Nassau County and upper 70s to 80 degrees for the Twin Forks.
Tuesday is expected to be in the upper 80s to lower 90s for most of the Island but in the lower 80s for the Twin Forks, he said.
The Fourth of July will have similar weather on Wednesday during the day, but meteorologists are predicting a slight chance of a passing shower or thunderstorm after 6 p.m. The North Shore has the highest chance — 30 percent — while the rest of the Island’s chance is at 20 percent.
Cloud cover on Wednesday evening will be 40 to 50 percent, Pollina said.