TAMPA, Fla. (WFLA) — Major heat is heading to the Southeast and Florida as a near-record heat dome grows across the region.

The heat is expected to start this weekend and last through most of next week, if not longer.

The incoming heat dome looks like it will impact a large swath of the United States with a bullseye in the Southeast.

A heat dome is a weather phenomenon created by an area of high pressure. That high pressure acts like a dome, the American Meteorological Society explains, trapping warm air underneath and keeping clouds and rain from coming in.

This upper level ridge is likely to break monthly records for the intensity of its high pressure. As a result, dozens of temperature records (highs and lows) are likely to be broken.

Over 30 million people will be under the threat of "extreme" heat, with another 50 million being faced with "major" heat, the National Oceanic and Atmospheric Administration predicts.

The heat will grow later this week and peak starting over the weekend. The most extreme conditions (shown in purple on the map below) move from Kansas and Oklahoma on Thursday eastward into the weekend. By Sunday, Missouri, Arkansas, Kentucky, Tennessee, southern Illinois, Alabama, Mississippi, Georgia and Florida will all be under the heat dome.

Highs will be in the mid-90s in Florida, reaching around 100 degrees across wide swaths of the southeast United States, from Oklahoma and Texas to the Carolinas.

A heat risk map shows hot and dangerous conditions spanning more than a dozen states. (Map: National Weather Service)

With very humid air in place, heat index numbers will peak between 105 and 115 degrees.

Overnight lows are expected to remain high across the Southeast, making for especially dangerous conditions.

"If you're talking heat waves, that nighttime low is incredibly important for determining total heat stress," said meteorologist Jeff Masters of Yale Climate Connections. "So if it doesn't cool off at night, your body doesn't have time to readjust to all the heat."

Although the heat will be most intense this weekend and into early next week, the heat dome looks likely to stick around for a while. It may still be in place come next weekend.

This comes just after the contiguous United States broke the record for hottest month ever in July.

July averaged 76.89 degrees Fahrenheit across the Lower 48 states, eclipsing the Dust Bowl's July 1936 by an eighth of a degree. Records go back to 1895.

"It's not good when you're breaking records from the Dust Bowl, which we are in this case," said Masters. "And that was a crazy sort of situation where you put tens of millions of people in motion. You had this great migration because of the drought and the heat that hit the center of the U.S. — just a cataclysmic event in U. S. history.

"If we're exceeding records from The Dust Bowl, that says that we're in deep trouble."

The Associated Press contributed to this report.

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