The hovering temperatures baking a lot of the desert Southwest this week will not be solely strikingly excessive but in addition unusually persistent.

In a forecast for the Phoenix space, the place the temperature on Monday was anticipated to succeed in 106 levels, the National Weather Service mentioned the period of the warmth wave could be “one of the longest, if not the longest, depending on how it’s measured.”

Sweltering temperatures are more likely to proceed for at the least every week within the space, probably approaching record-breaking ranges by the weekend, based on Tom Frieders, a meteorologist with the Weather Service in Phoenix.

Nighttime temperatures there this week will barely dip beneath 90 levels, and even the cooling thunderstorms that usually accompany monsoon season, which begins round this time of 12 months, have been lagging.

“This year, we are seeing a bit of a delay in the evolution into the monsoon thunderstorm season,” Mr. Frieders mentioned. “And so with that, we ended up seeing temperatures a little bit hotter during the day.”

The warmth wave now stationed over the desert Southwest — attributable to a “heat dome” of excessive strain — has additionally introduced sweltering temperatures to elements of Texas and New Mexico. Experts estimate that more than 50 million people throughout the United States stay within the areas anticipated to have harmful ranges of warmth.

“It looks like it’s going to be pretty oppressive around here,” mentioned Capt. Darren Noak of the Austin-Travis County Emergency Medical Services, which carried out a helicopter rescue on Sunday to deal with an individual who had been overcome by the warmth in a preferred mountaineering spot west of Austin, Texas.

As Captain Noak spoke on Monday afternoon, the heat index within the metropolis — a measure of how the air feels that takes under consideration each temperature and humidity — was climbing towards an anticipated excessive of 109 levels.

Captain Noak mentioned Austin residents had loved some reduction final week, when excessive temperatures fell wanting 100 levels for a number of days and the E.M.S. made solely 39 heat-related calls, in contrast with 74 the earlier week.

But now, “the weather predictions are for above 100-degree temperatures for at least the next two weeks straight,” he mentioned. “I would imagine this week is going to shoot back up there again.”

Orlando Bermudez, a forecaster for the Weather Service in Austin, mentioned residents of central Texas might “copy and paste” the identical primary forecast for the following couple of weeks: sizzling and dry.

“The story of the week into the weekend into next week is heat,” he mentioned, predicting a just about unbroken sample of triple-digit temperatures most certainly extending at the least by July 20.

Julie Engel, the president of the Greater Yuma Economic Development Corporation in southwest Arizona, mentioned residents within the space had been coping with these sorts of temperatures for a very long time.

“It’s really not anything out of the ordinary for us,” she mentioned. Construction crews and farmworkers know tips on how to adapt, she added, for instance by beginning their workdays hours earlier than daybreak.

Still, temperatures throughout the area are harmful for many individuals, based on Zack Guido, an assistant analysis professor on the Arizona Institute for Resilience in Tucson.

“Most challenges associated with these extreme climate conditions fall on people with less resources,” Dr. Guido mentioned, including that top nighttime temperatures solely added to the chance.

“If you don’t have air-conditioning at night, and the temperatures remain above 90 degrees Fahrenheit, that has been attributed to physiological stress that can be quite harmful,” he mentioned.

John Washington contributed reporting.