From a story on axios.com by Andrew Freedman headlined “Relentless heat wave spreads across southern U.S.”:

A “relentless” and historic heat wave continues to bring potentially deadly temperatures from the West and Southwest across the South Central states, with more records forecast to fall.

The big picture: Over 104 million people were under heat alerts Monday evening, stretching across a dozen states from Nevada to Florida, according to heat.gov.

The National Weather Service forecasts the heat to expand this week, as triple-digit highs continue in the Desert Southwest and southwestern Texas, while oppressively humid temperatures in the mid-to-upper 90s affect the Mid-South and Gulf Coast.