A freak, late-summer heat wave is expected to roast over 80 million Americans as a new map reveals several states are now in the midst of their hottest summer in history.

Meteorologists with AccuWeather have revealed that 2026 was the hottest summer on record for Arizona, Colorado, New Mexico and Utah.

Several states throughout the country saw their summer months - June, July and August - soar into the top five all time, including California, Nevada, Idaho, Texas, Louisiana, Florida, the Carolinas, Delaware and Maine.

Now, a massive high pressure system has moved in over the southern US, creating another heat dome over parts of 16 states from the Gulf Coast to Central Illinois.

Temperatures in states like Texas, Arkansas and South Carolina are expected to approach 100 degrees Fahrenheit on Monday - which would challenge or break records which have stood for decades.

The National Weather Service (NWS) has also issued heat advisories in 12 states, warning that the heat index values will climb to between 105°F and 111°F throughout the region.

The heat index is the 'feels like' temperature, which is hotter when the air is more humid. On a 90-degree day, high humidity can make the 'feels like' temperature reach 105°F.

The high heat is expected to last at least through Tuesday. This latest heat wave is striking the South just days after climate experts declared August 2026 to be the hottest month ever on Earth.

Officials have warned that this week's heat wave will likely send temperatures throughout the South five to ten degrees higher than the normal average for mid-September.

Widespread heat reaching from the upper 80s to the upper 90s is expected for states trapped under this late-season heat dome.

A heat dome acts like a steam cooker, keeping heat and humidity from rising into the atmosphere and cooling the states the high pressure is blanketing.

The hottest conditions this week are expected to hit Texas, Oklahoma, Louisiana and Arkansas, where meteorologists are predicting the heat to reach 100°F.

San Antonio could break a 15-year-old record on September 14, as the forecasted high of 98°F will be just one degree off the city's all-time high on this date.

Meanwhile, in Fort Smith, Arkansas, AccuWeather said Monday's high will likely reach 102°F, breaking a record set over two decades ago in the year 2000.

NWS warned: 'Hot temperatures and high humidity may cause heat illnesses. Drink plenty of fluids, stay in an air-conditioned room, stay out of the sun, and check up on relatives and neighbors.'

There have been multiple heat domes recorded this summer, spanning from the West Coast to the Northeast, creating record daily temperatures in major cities throughout the US. 

AccuWeather Expert Meteorologist Tyler Roys said in a statement: 'What stands out is how widespread and persistent the warmth has been, from the atmosphere to the oceans.'

Roys warned that the emergence of El Niño this summer could continue to impact weather patterns around the world this fall and winter.

After July 2026 was declared the hottest month in the continental US, AccuWeather Expert Meteorologist Alyssa Glenny said: 'Record heat remains rare, but it is happening more frequently.' 

'As average temperatures rise, the baseline that these extremes build from is getting warmer. That means it doesn’t take as much for a period of extreme heat to push temperatures into record territory.'

AccuWeather noted they used data from the NOAA Centers for Environmental Information (NCEI) for their new map, which has been keeping climate records for 132 years.

In Arizona, which experienced its hottest summer ever, the temperature was over five degrees higher than an average summer this year.