Although the summer heat is just getting started in the Eastern United States, it’s reaching critical mass in the West. All-time records could be broken early next week in Arizona, and the blaze is going to continue.

Early next week, the temperature in Tucson will climb above 110 degrees. In Phoenix, the forecast for Tuesday is 120, which looks to be the hottest day of the week for the city.

Triple-digit highs are in the forecast for Northern California — including the Sierra Mountains.

It’s “starting to sound like a broken record,” the National Weather Service in Phoenix wrote Friday morning, “but that’s because we will be breaking records next week.”

“There’s absolutely no doubt we will be near all-time highs with this heat wave,” the forecasters continued, “with the hottest and most dangerous temperatures expected Monday through Wednesday.”

Record highs

Phoenix — 122 degrees (June 16, 1990)
Tucson — 117 degrees (June 26, 1990)

This heat wave is right on time. In the weeks leading up to the beginning of monsoon season, temperatures in Arizona, New Mexico, southern Nevada and Southern California typically climb to the highest they’ll be all year.

Southwest Monsoon, which occurs annually, is actually triggered by the very heat looming in the forecast early next week. The buildup of warmth creates a large-scale trough of low pressure that extends from Mexico to Arizona, Southern California and Nevada. Air flows away from high pressure and toward low pressure, so moisture is drawn over the Southwest.

Tucson, for example, experiences its wettest months in July and August, although the monsoon can last through September.

This blazing, magenta graphic from pretty much sums up the forecast for the coming week. “H” stands for high pressure. In this case, it also stands for HOT.

The extreme heat will extend into Northern California, where the Weather Service is predicting triple-digit highs through next week in the Central Valley. Even the mountains will get a taste of the summer heat wave with temperatures as hot as 105 degrees.

The reason it can get so hot in the Southwest is that the humidity is so low. Perhaps it’s counterintuitive, but in the Eastern United States — where summer humidity can be oppressive — the presence of moisture in the air keeps the temperature down.

In the Southwest, there’s no moisture in the ground for the sun’s energy to evaporate. So, instead, it goes toward making the air hotter and hotter.

The best thing you can do during a heat wave like this is stay indoors. If you’re working outside, take frequent breaks to rehydrate and cool your body. You may not realize you’re overheating,  because sweat evaporates instantaneously in such dry conditions, but you can quickly suffer from heat stress in these conditions.

The National Weather Service in Las Vegas offers these simple tips for the impending inferno — including the advice to forgo the caffeine and alcohol, which increase dehydration. Hopefully, Sin City gets the memo.

This post has been updated.