Heat wave scorches millions in Texas, Louisiana: Temperatures could feel like 120 degrees

More than 25 million Americans were again under an excessive heat warning Saturday, with one of the nation's largest cities opening emergency cooling centers within libraries and other public buildings for vulnerable residents.

The National Weather Service on Saturday forecast heat indexes near Houston and San Antonio as high as 120 degrees Fahrenheit.

The extremely hot temperatures "will likely tie or break records" — and would do so ahead of the official summer solstice on Wednesday, the weather service said Saturday.

Residents in Texas and Louisiana are being told to drink plenty of fluids, stay in an air-conditioned room, stay out of the sun and check in on relatives and neighbors.

"This is dangerous heat," said AccuWeather senior meteorologist Michelle McLeod. "Some records are going to be challenged."

Some of the nation's largest cities will swelter through next week, including Houston and San Antonio, forecasters say.

Austin, Texas, and Corpus Christi, Texas, along with New Orleans and all of southern Louisiana will also feel the excessive heat and there's increased risk of wildfires being sparked in some areas, the weather service said Saturday.

Houston's excessive heat warning

This week's excessive heat warning issued for Houston is the city's first in nearly seven years.

The temperature on Friday in Houston rose to 95 degrees Fahrenheit, with a heat index of 111 degrees. The temperature in Corpus Christi was also 95 degrees by Friday afternoon, but its heat index swelled to 119 degrees. Heat index values reflect how it actually feels outdoors by considering the temperature and relative humidity.

“We do see these temperatures most summers. The thing that’s different about this particular heat episode is that it’s earlier than we normally see it,” said Tim Cady, a meteorologist with the weather service in Houston/Galveston.

Cady said a "really persistent" band of high pressure sitting over the south-central U.S. is to blame for the extremely hot temperatures.

“It could be well into next week before we really see any relief from this,” he said.

Heat 'emergency plan' in Houston

Earlier this week, Houston launched a public health heat emergency plan, which included making all city libraries and other locations into cooling centers six days a week.

“We all know Houston sometimes can be uncomfortably hot in the summer. I want everyone to understand this forecast calls for heat and humidity that is dangerous and potentially deadly for some of our vulnerable Houstonians,” Mayor Sylvester Turner said this week.

Similar cooling centers have also been opened in Austin, Corpus Christi and Laredo.

How to stay safe from the heat

With the long Juneteenth holiday weekend, Cady said people should take precautions during the dangerous heat, including avoiding strenuous activity during the day and wearing light clothing.

“We’re really stressing heat safety this weekend,” Cady said.

In general, unusually high temperatures should be taken extremely seriously, said Bianca Feldkircher, lead meteorologist at the National Weather Service in Phoenix.

There are various ways to stay safe in a heat wave:

It is important to limit any kind of outdoor activity during the hottest parts of the day, said Feldkircher. If you can avoid going outdoors during those times, try to put off activities until the morning or after the sun goes down.

Staying hydrated is also key to staying safe in heat waves. According to the Red Cross, on average, a person should drink approximately 3/4 of a gallon of liquids per day.

Eating foods that have a high water content, such as fruits and vegetables, can also keep you hydrated, said Feldkircher.

The Red Cross also advises to keep your home cool by doing the following:

• Covering windows with drapes or shades.

• Installing air conditioners and insulation around them.

• Using window reflectors to send heat back outside.

Severe thunderstorms in Oklahoma, Arkansas

As a dome of hot, humid air lingers over much of Texas and Louisiana, thunderstorms are likely to form around it to the north, forecasters at AccuWeather reported Saturday.

Already this week, the intense thunderstorms "have bombarded areas" with damaging winds, hail and torrential downpours, meteorologists at AccuWeather said. Severe storms led to deadly tornadoes that killed a total of five people in the Texas panhandle, Florida and Mississippi.

Contributing: Olivia Munson, USA TODAY; Associated Press

This article originally appeared on USA TODAY: Excessive heat warnings as heat wave hits Texas, Louisiana, NWS says