BIRMINGHAM, Ala. (AP) — Forecasters are warning about days of scorching, dangerous heat across a wide stretch of the U.S. South and Midwest, where the heat index will feel as high as 117 degrees in some spots.

With temperatures around 100 degrees at midday Monday and “feels like” temperatures soaring higher, parts of 13 states were under heat advisories, from Texas, Louisiana and Florida in the South to Missouri and Illinois in the Midwest, the National Weather Service reported.

“It feels like hell is what it feels like,” said Junae Brooks, who runs Junae’s Grocery in Holly Bluff, Mississippi.

Many of her customers were wearing straw hats or keeping cool with wet rags around their necks, she said.

Some of the most oppressive conditions were being felt in Louisiana, Arkansas, Mississippi and Oklahoma. Tuesday will be about the same, forecasters said, and Wednesday will be only a little cooler.

The temperature hit 100 degrees (37 Celsius) with a heat index of 106 degrees  by mid-afternoon in Birmingham, where forecasters said they last issued an excessive heat warning seven years ago.

It was expected to feel like 116 degrees (46.7 Celsius) in parts of eastern Oklahoma, near Tulsa, on Monday, forecasters said. And parts of Arkansas just west of Memphis, Tennessee, could see heat indexes Monday of around 117 degrees.

Heat exhaustion and heat stroke are among the main threats in those areas.

“You are more likely to develop a heat illness quicker in this type of weather, when it’s really humid and hot,” said Gary Chatelain, a National Weather Service meteorologist based in Shreveport, Louisiana.

Stifling humidity is hanging in the Louisiana air partly because the area has seen such a wet summer, Chatelain said.

More of the same is in store for Tuesday, when heat and humidity will again make for dangerous heat indexes. However, an approaching cool front should help ease the intense heat by Wednesday, Chatelain said.

“If you’re going out in the summer, prepare for the worst,” he said.

That means people spending time outdoors should take breaks in the shade, drink plenty of water, wear hats and light-colored clothing, among other precautions, he said. Anyone who stops sweating in the heat should be aware that it might be a sign of heat illness.

But in the Mississippi Delta region, farmers did not have a choice but to work in the fields Monday since they’re scrambling to make repairs and get caught up after floodwaters inundated the region in recent months, Brooks said. The flooding — which involved an area larger than New York City and Los Angeles combined — has recently receded and the farmers are just now able to reach their land and begin cleaning up the mess left behind.

“The mosquitoes the gnats, the spiders, the snakes — all of them — have been way worse this year,” Brooks said of the land known locally as the Yazoo backwater area.

In Alabama and Tennessee, high school football coaches were adjusting practice schedules Monday and Tuesday, with some moving the workouts indoors and others conducting training in the early morning or evening, The Tennessean reported .

Cooling stations were open in several cities, including Tulsa, Memphis, and Little Rock, Arkansas, officials said.

In northern Alabama, forecasters with the weather service’s Huntsville office said Monday they issued the first “excessive heat warning” for the area in more than seven years. Such a warning is more serious than a heat advisory.

The region hardest-hit by this week’s heat wave could experience many more days each year when the heat index soars as the effects of climate change increase, scientists say.

Historically, cities such as Austin, Texas; Baton Rouge, Louisiana; Jackson, Mississippi; and Tallahassee, Florida experience less than a week’s worth of days each year when the heat index is over 105 degrees (41 Celsius).

If no action is taken to stop climate change, the number of days when it’s that hot will soar in those cities and others, according to a recent study by the Union of Concerned Scientists, “Killer Heat in the United States .” By midcentury, Austin would see 59 days of such extreme heat in an average year. The number of days would increase to 57 in Baton Rouge; 52 in Jackson; and 50 in Tallahassee.

Southern states will feel the brunt of increasingly dangerous heat in coming years, said Astrid Caldas, one of the study’s authors.

“Texas and Florida stand out, but also of course Louisiana, and Mississippi and the whole area all the way up to North Carolina,” said Caldas, a climate scientist.

One reason the study focused on heat index values — the so-called “feels-like” temperature — is because the combination of high air temperature and high humidity can have dangerous health consequences for people, Caldas said.

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Martin reported from Atlanta.