The Southwest United States is about to endure a heat wave that could rank among its worst in history — both for its intensity and longevity according to MSN.

The heat wave will affect much of Arizona and New Mexico and build into interior California, probably peaking during the second half of next week. The National Weather Service office in Phoenix says it will “rival some of the worst heat waves this area has ever seen.”

While it’s already excessively hot in the region, it will get significantly worse next week, and it’s unclear when the heat will ease.

Computer models that project the weather 16 days into the future “do not show an end to this heat wave,” the Weather Service wrote in a discussion. “This should go down as one of the longest, if not the longest duration heat wave.”

While summer started off tame in the region (Las Vegas didn’t hit 100 until June 30, ending a record streak of not hitting the century mark), the heat began to ramp up quickly in recent days.

In Phoenix, it was 115 degrees on Thursday, following 116 on the Fourth of July. The temperature in Death Valley, Calif., soared as high as 126 in the past week.

An excessive heat warning is in place through at least July 13 for much of south-central Arizona, including Phoenix and Tucson.

In addition to a week or more of days with extreme heat, temperatures won’t drop too far at night, offering little relief and posing a health risk for those without access to air conditioning.

“Very dangerous to potentially life-threatening heat conditions are expected through next week and it is very essential that all the necessary heat precautions be taken to avoid any heat-related illnesses,” the Weather Service wrote.

It’s not just the heat. Unusually low humidity for July across the region is mixing with high temperatures, exacerbating a wildfire risk by drying out the land surface.

Red-flag warnings for high fire danger are posted for northern Arizona and the Four Corners region out of concern for the potential of fast-moving blazes, several of which are already scorching land.