The air feels thick across southern Indiana heading into July 4th weekend.

Temperatures today hit 93 degrees, and humidity tonight is expected to reach 97 percent. Heat indices are expected to peak at more than 100 Friday and Saturday.

Indiana weather today is effectively the same as in the Amazon Rainforest, according to AccuWeather.

The National Weather Service has posted Extreme Heat Warnings across the state this weekend. The heat wave is courtesy of air coming from the Gulf of Mexico, said Regional Climatologist Melissa Widhalm.

“What we're experiencing right now, these last few days, is actually the result of warm, moist air flowing up from the Gulf region and into our region,” Widhalm said. “We're moving moisture from that humid tropical area of the country into the Midwest.”

That moisture isn't making temperatures hotter, she said, it's making it harder for the body to cool itself.

“When the humidity is very high and we cannot sweat to cool down our bodies, it makes it feel a lot hotter than that air temperature is,” Widhalm said. “Air temperature alone is only one part of the story. We need to know the moisture, which is where that humidity level comes in, and when we combine the two, that's where we get the heat index.”

Listen: A Moment of Science: It's not just the heat, it's the humidity

The conditions have prompted heat safety warnings from the National Weather Service and the American Red Cross. The organizations recommend limiting outdoor activity during the hottest parts of the day, staying in air-conditioned spaces, drinking plenty of water, and watching for signs of heat-related illness.

Widhalm said the humidity will return later in the summer from evapotranspiration, colloquially called "corn sweat."

As corn matures in late July and August, a single acre of healthy corn can release thousands of gallons of water into the atmosphere each day through evapotranspiration.

Indiana is the nation’s fifth highest corn-producing state, growing millions of acres of corn per year, according to the U.S. Department of Agriculture.

“We're still a bit early for the corn evaporation and transpiration to be at its peak, so we're several weeks out from that,” Widhalm said. “You wouldn't know it, because it is soupy out there, and that is thanks to the Gulf.”

Widhalm says stretches of dangerous heat like this are typical for the Midwest, which averages three or four days each year with a heat index above 100 degrees. Forecasts show some relief arriving early next week after the holiday weekend.

Read more: Dangerous heat expected across central Indiana

Until then, she says, people should take the heat seriously.

“Heat stress, heat exhaustion, heat stroke, those are no joke,” Widhalm said. “The most serious threat right now, here over these last few days and these next couple days, is the safety of humans and animals.”

She also said people should check the National Weather Service's HeatRisk tool and keep an eye on neighbors, friends and family who may be especially vulnerable during the extreme heat.

“We're going to get a little bit of relief at the end of the weekend,” Widhalm said, “but nothing quite says freedom in America like a really hot, humid Fourth of July.”