Heat wave sweeps across southern US, prompting warnings and energy-saving tips.

More than 25 million Americans are under an excessive heat warning, with temperatures in Texas and Louisiana expected to feel like 120 degrees Fahrenheit. Emergency cooling centers have been opened in libraries and other public buildings for vulnerable residents. The National Weather Service warns of increased risk of wildfires being sparked in some areas. Residents are advised to drink plenty of fluids, stay in an air-conditioned room, stay out of the sun and check in on relatives and neighbors.