Summer officially starts on Tuesday, and things are already heating up to dangerous levels across the Southwest, with heat advisories in effect until Saturday.

Arizona, Nevada, and Southern California are expected to see record-high temperatures in the coming days. In Phoenix, temperatures could exceed 120 degrees farenheit, raising concern about potential heat-related deaths. Last year, 130 people died from extreme heat in the city—the most in the last decade.

If the temperature does exceed 120 degrees, that'd be the fourth time in the city's recorded history, NBC News reported.

National Weather Service - weather.gov

What's behind this heat wave?

It's impossible to single out one reason for this extreme weather. But climate scientists have predicted that such weather patterns would become more frequent as the climate heats up.

"There are clear signs that heat waves will tend to become longer and more intense as our climate warms," meteorologist Bob Henson told Gizmodo. "This doesn't mean every heat wave will be a record-setter, but more and more of them will be."

Henson said the "duration" of the heat wave will be one of its "hallmarks." Not only will temperatures reach record highs throughout the southwest, but the high temperatures will be prolonged over a stretch of three to four days, according to the National Weather Service.

Experts are urging residents—especially elderly residents—to avoid doing strenuous work outdoors during the day, drink fluids, stay in shaded or air-conditioned spaces, and be aware of the signs of heat exhaustion (nausea, headache, fatigue).