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Long Island weather: Heat wave, advisory for holiday weekend

A heat wave is defined as at least

A heat wave is defined as at least three days of temperatures hitting or topping 90 degrees. Credit: Weather Underground

Residents and visitors should know that Long Island was expected to see hot weather conditions from Saturday through Monday, at times dangerously so, with humidity added in, forecasters say.

That will be more so for Nassau County, where a heat advisory is in effect from noon Saturday to noon Sunday, to be followed by an even more serious excessive heat watch Sunday afternoon to Monday evening, the National Weather Service said.

The temperature and humidity level combined could make it feel like the upper 90s on Saturday afternoon and evening, the weather service said, and as high as 107 in the afternoon and early evening of Sunday and Monday.

As the heat index — or "feels-like" temperatures — tip into the low 100s, such “extreme heat can cause illness and death” for those who are most vulnerable and can’t find a way to stay cool, the weather service said. Also, it said, “heat and humidity may cause heat stress during outdoor exertion or extended exposure.”

Suffolk is far from escaping, though, with a heat advisory issued for the western part of the county from noon Sunday to 9 p.m. Monday. An advisory was issued for Suffolk east of the William Floyd Parkway from noon to 9 p.m. Sunday. Temperatures are expected to feel like they are around 100 degrees.

Add to that an air quality alert for Saturday, meaning elevated levels of ozone.

There are chances for “a prolonged heat wave for much of the Island,” said Jay Engle, weather service meteorologist in Upton. That means potential for three consecutive days or more seeing temperatures, without the humidity factor, hit 90 or above.

This heat comes courtesy of “a large area of high pressure” settling to the south and southwest, with humidity becoming “more noticeable Saturday night into Sunday,” the weather service said.

Look for heat and humidity to continue into early next week, Engle 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.

An excessive heat watch comes into play when an area is expected to experience combined heat and humidity conditions that “could create a dangerous situation in which heat illnesses are possible.” That would be for when a feels-like temperature of 105 degrees or more is expected for two consecutive hours.

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