(Reuters) -A dangerous heat wave that helped spawn deadly tornadoes in Texas and Florida threatened on Friday to bring more extreme weather to the U.S. South, prompting the National Weather Service to warn Americans to limit time outdoors over the long Juneteenth weekend.
At least four people were killed in twisters that touched down on Thursday in the panhandles of Texas and Florida, where flooding also forced almost 150 people out of their homes, officials said.
Power was out to nearly 500,000 customers in Texas, Louisiana and Mississippi on Friday, according to Poweroutage.us.
A mix of high humidity and temperatures above 90 degrees Fahrenheit (32 degrees Celsius)could push heat index values above 115 in some parts of the South this weekend, National Weather Service meteorologist Matt Mosier said. The combination could cause atmospheric instability and create conditions ripe for more destructive storms.
"It's just been very humid and muggy out," Mosier said. "You'll end up getting strong gusts and large hail, and even with a few of these storms, you can get tornadoes as well."
The agency issued excessive heat warnings affecting millions of people in parts of southern Louisiana and Texas, saying the heat index could reach 110 degrees. South Florida and Mississippi were under heat advisories for Friday.
It recommended that people drink fluids to keep hydrated, stay in air-conditioned rooms and limit time in the sun.
President Joe Biden was briefed on the weather conditions on Friday morning, White House spokesperson Olivia Dalton told reporters aboard Air Force One while Biden traveled to an event in Connecticut. Afterwards, the president committed to offering federal assistance, she said.
While southern states are accustomed to high heat during the summer, extreme weather conditions have become more frequent and intense across the country in recent years. Climate change is driving the trend, scientists say.
The tornado that struck in the Texas Panhandle town of Perryton killed at least three people and injured dozens of others. Hundreds of homes, many of them in a trailer park, were damaged or destroyed.
In Pensacola, on Florida's Panhandle, a tornado downed power lines and toppled a tree onto a home, killing one person inside, Escambia County spokesperson Davis Wood said. Heavy rainfall also forced 146 residents to evacuate an apartment complex in the city of Warrington, he said.