The heat index, how hot it feels when temperatures are combined with humidity, will reach over 100 degrees across most of New Jersey on Wednesday, according to the National Weather Service.

By Cassidy Grom | NJ Advance Media for NJ.com

It was hot Tuesday, but Wednesday is going to be sweltering - with even higher temperatures and oppressive humidity in the forecast. The National Weather Service placed all of New Jersey and much of the surrounding states under a heat advisory Tuesday, and the advisory lasts until 8 p.m. Wednesday.

"The heat and humidity may cause heat stress during outdoor exertion or extended exposure," the weather service advisory said. Making matters worse, especially for people with breathing problems, is the bad air quality across most of the Garden State region on Wednesday.

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Courtesy AccuWeather

How to stay safe

Hot temperatures and high humidity combined will create situations where heat illnesses are possible. The National Weather Service recommends the following:

Drinking fluids

Staying in air-conditioned rooms

Stay out of the sun

Check in on vulnerable relatives and neighbors

Take frequent breaks if working outdoors

If anyone experiences heat stroke, move them to a shaded area and call 911.

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NJ Advance Media file photo

Is this normal?

No. Not really.

Average temperatures across the state in June were only slightly above normal, making it the 42nd warmest June since records started being kept in 1895, according to New Jersey State Climatologist David Robinson at Rutgers University.

Last month, New Jersey tied its 15th warmest July on record, with an average statewide temperature of 76.1 degrees, Robinson's stats show. Statewide statistics for August won't be finalized until early September, but Robinson says this could turn out to be New Jersey's hottest August on record.

If not, it will likely land in the top two or top three, he said.

So far, temperatures this month at the National Weather Service’s major climate sites in New Jersey have been running considerably above normal — 2.6 to 4.6 degrees hotter than usual. That's not including Wednesday's forecast highs in the mid-90s and Thursday's forecast highs near 90.

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How many heat waves?

If the temperature Wednesday reaches the 90-degree mark - which is a sure bet, with forecasters calling for a high of 97 this afternoon - this will be the fifth official heat wave of the summer in the Newark region.

It will be the fourth heat wave of the summer in the Atlantic City area, and only the third heat wave of the summer in the Trenton area.

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Another hot and humid day is in store across the Tri-State. Temps will quickly rise into the 90s with heat index valued 98 to 104 this afternoon. A heat advisory remains in effect until 9 pm. Make sure you know heat safety and never leave kids or pets unattended in vehicles. pic.twitter.com/9KSdlNv9yV — NWS New York NY (@NWSNewYorkNY) August 29, 2018

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NJ Advance Media staff writer Len Melisurgo contributed to this report. Cassidy Grom may be reached at cgrom@njadvancemedia.com Follow her at @cassidygrom. Find NJ.com on Facebook.Have a tip? Tell us. nj.com/tips