A relentless heat wave is expanding across the South. Heat alerts are in effect from southeast Arizona through most of Texas to Mobile, Alabama and Pensacola, Florida.
Nearly 40 million people are under alerts total.
Temperatures could get as high as 113 degrees in Tucson, Arizona. In Mobile, Alabama, the heat index is up to 110 degrees. In Abilene, Texas, it's so hot cookies bake in the back of a car.
And the heat hazard is expected to expand as the Fourth of July approaches.
Big Bend National Park Ranger Tom Vandenberg says an investigation is underway, but it's believed heat reaching 119 degrees at the park played a factor in the stepfather's death.
He says this year four visitors have died at the park, adding that the 14-mile trail the Florida family embarked on is dangerous in the summer, with rugged terrain and no cell service, shade or water.
Experts and officials say in temperatures like these, any strenuous activity should be done early in the morning or late in the evening once things cool off.
"The message is, don't think you can just push through the heat. Pay attention to your bodies and be aware and be very careful," said Kirk Watson, mayor of Austin, Texas.
