PHOENIX (AP) — Dangerously hot temperatures are on the way throughout the Southwest.

An excessive heat warning prompted health officials in Arizona to reschedule outdoor COVID-19 vaccination operations, fire officials to rotate crews working major blazes and the U.S. Border Patrol to issue reminders about the dangers of crossing the desert.

The warning issued by the National Weather Service for high temperatures of up to 118 degrees (47.7 C) for desert areas of south-central Arizona is set begin Saturday and extend to next Friday.

The warning “means that a period of very hot temperatures, even by local standards, will occur,” the weather bureau in Phoenix said.

Forecasters said people should try to stay indoors, drink more water than usual, and check on family, friends and neighbors, especially the elderly.

Heat warnings and advisories also were issued for large parts of California, Nevada and New Mexico — where the city of Las Cruces opened cooling stations for residents and, particularly, the elderly and people at high risk for heat-related illness.

Cooling stations also will be open in southern Nevada next week.

The Salvation Army announced Friday it would activate 11 heat relief stations in metro Phoenix where people can get water and cool off in buildings with air conditioning.

Salvation Army personnel also will deliver water to people living nearby, and the organization will send a mobile hydration unit to homeless encampments, officials said.

Additional hydration stations will be operated by local governments and nonprofits at libraries, public pools, churches and other community sites in the Phoenix area.

Because of the forecast midday heat in Tucson, mobile COVID-19 vaccination units will change their hours, operating Saturday through Monday for four hours beginning at 7 a.m. and then again for three hours beginning at 7 p.m., Pima County officials said.

That's to avoid subjecting clients, workers and volunteers to the expected temperatures of over 105 degrees (40.5 C) for sustained periods, officials said.

The Phoenix Fire Department said high temperatures already are a concern for crews fighting large fires.

Firefighters on Thursday took turns using hoses and ladder-mounted cannons to fight a fire at a metal recycling yard that took hours to extinguish, with firefighters rotating off to drink water and cool down, the department said.

The Border Patrol said migrants put their lives at risk when they cross the Sonoran Desert in the summer.

In southern New Mexico, heat was suspected in the death of a person who collapsed near an elementary school in Sunland Park on Thursday near the U.S.-Mexico border, the agency said.

Last week, Border Patrol agents in the Yuma Sector to the west found the remains of two migrants who died in separate locations: a 40-year-old Mexican man and a 20-year-old Guatemalan woman.

Adults traversing the desert in summer heat must drink at least two gallons (7.5 liters) of water daily to survive, the agency recommended.