Some 35 million people in southern Texas, Louisiana and Florida were under excessive heat warnings, watches and advisories from Thursday through the three-day Juneteenth weekend, the National Weather Service said.
"It wouldn't be an active summer weather pattern without oppressive heat and much of Texas and the Deep South will have plenty heading into the beginning of the holiday weekend," the service said in its forecast, which included the chance of strong thunderstorms and possible tornadoes for the region.
The growing frequency and intensity of severe weather across the U.S. is symptomatic of human-driven climate change, climate scientists say.
Record-breaking heat index temperatures could reach 115 in places such Austin, the Texas state capital, where officials have opened cooling centers in libraries and park buildings and urged people to drink plenty of water and stay out of the sun.
The Electric Reliability Council of Texas (ERCOT), which operates the grid for more than 26 million customers representing about 90% of the state's power load, has said it has enough resources to meet demand.
Across southern Louisiana, similar sky-high temperatures were in the forecast. New Orleans residents woke up to a brutal 96-degree heat index, the weather service said in a tweet. "Dat's some bayou weather right there," the agency said in the local parlance.
Triple-digit temperatures and drenching humidity will also smother South Florida over the next several days, including in cities such as Miami and Jupiter, where officials warned residents to not leave pets and children alone in hot vehicles.
"I live in Lava Land in sunny Florida," a Twitter user who goes by the name of RyDavis wrote in a post early on Thursday morning.
(Reporting by Brendan O'Brien in Chicago; editing by Jonathan Oatis)
