The Southwest is bracing for intense heat as a looming wave of high temperatures has prompted extreme heat warnings and advisories for 80 million people stretching from the U.S.-Mexico border to southwestern Utah.

According to federal weather experts, a rotating system of warm, sinking air over the area where Arizona, Utah, Colorado, and New Mexico meet will intensify the heat across the region throughout the weekend.

“An unusually strong high-pressure ridge positioned over the Four Corners states is set to cause a considerable heat wave,” the National Weather Service noted in a national forecast discussion on Tuesday.

Extreme heat warnings, signaling imminent danger, begin Wednesday morning in Southern California. These include parts of Los Angeles, San Diego, and Orange counties, as well as Palm Springs. Warnings also start Wednesday for Las Vegas, Phoenix, and Tucson, Arizona, and they are likely to continue through the weekend.

Los Angeles Mayor Karen Bass mentioned that the city is preparing for “possibly some of the summer’s hottest temperatures.” In response, cooling centers are being set up in the city, and Governor Gavin Newsom is relocating firefighting resources to the area.

In El Centro, California, an agricultural hub where nighttime temperatures stayed in the triple digits, a child left unattended in a hot car on Monday died later at a hospital, according to police reports.

Temperatures in the 90s are expected as far north as the Seattle region Saturday, according to the service, and Portland, Oregon, has a fire weather watch in effect for Thursday.

On Friday, Phoenix is expected to reach a high temperature of 112 degrees, Las Vegas is expected to reach 110, and Death Valley National Park’s Furnace Creek Visitor’s Center is forecast to report 120 degrees, according to the weather service.

Maricopa County, Arizona, officials on Tuesday reported 44 deaths last week for which heat was a cause or contributor.