Long Island weather: Heat index near 100 Tuesday, Wednesday

Parts of Long Island will be under a heat advisory Tuesday and Wednesday as heat index values rise into the low 100s amid humid conditions.

The National Weather Service said Nassau County will be under a heat advisory beginning at 11 a.m. Tuesday through 9 p.m. Wednesday. The advisory extends to western Suffolk County on Wednesday during the same period.

"The next few days are going to be a heat wave, maybe not technically in every little location here on Long Island, but in general," said Dominic Ramunni, a meteorologist with the National Weather Service's Upton office.

Tuesday will reach heat index values in the mid to upper 90s. Eastern Long Island will feel cooler compared to advisory areas due to the trajectory of winds off the water, said weather service meteorologist Nelson Vaz. 

"Once you get away from those south coastal areas tomorrow, we'll be around 90 degrees, and with the added humidity, it's going to make it feel like it's somewhere in the mid '90s," he said.

An air quality advisory will also be in effect from 11 a.m. to 11 p.m. Tuesday.

The National Weather Service recommends limiting strenuous outdoor activity, particularly for people who are sensitive to poor air quality or have preexisting respiratory conditions.

Wednesday will be the hottest day of the week, with heat index values reaching as high as 105 degrees as winds decrease. Forecasters said there remains some uncertainty about how far east the highest heat index values will extend, particularly along coastal locations.

The heat wave during the July Fourth weekend brought heat index values that felt as high as 110 degrees across the New York City region. Tuesday and Wednesday's heat will be "a few degrees cooler in terms of severity," Ramunni said.

Forecasters encourage everyone to take precautions in the hot and humid conditions, such as keeping hydrated, staying inside air-conditioned spaces and limiting strenuous activity outside.

"Those are all important things to do, especially in the peak of the heat during the day," Vaz said.

Thursday and Friday see temperatures in the upper 80s to lower 90s — more typical summer weather, Vaz said, but will feel significantly cooler because of a break in the humidity.

Ramunni said: "It's important to know the warning signs of heat-related illness. Heat exhaustion, you start to get dizzy, you stop sweating, you become clammy. That can be a serious medical incident that you want to take seriously and get into cooler air as soon as you can if you notice something like that," Ramunni said.

Newsday's Ava Shea contributed to this story.