Four Dead as Heat Intensifies in Southwest States, Millions Under Heat Warning

iStock/Thinkstock(PHOENIX) — Four people were killed in Arizona and millions more remain under a heat warning advisory following an intense heatwave that impacted several states Sunday.

A male and female hiker died Sunday in Arizona's Pima County due to heat-related illnesses, according to the Pima County Sheriff's Office.

In nearby Phoenix, a 28-year-old female trainer died Sunday, according to the Phoenix fire department. A 25-year-old male hiker also died of heat exposure in the Superstation Mountains on Saturday, according to the Pinal County Sheriff's Office.

Record highs were reported in New Mexico, Arizona, Nevada and California. The mercury in Yuma, Arizona, hit 120 degrees, according to ABC News meteorologist Max Golembo.

The National Weather Service in Phoenix also reported a high of 118 degrees at Sky Harbor International Airport, breaking the previous record of 115 degrees that was set in 1968.

Monday will be the hottest day of the week as temperatures in some areas will rise above 120 degrees, said Golembo.

Excessive heat warnings are in place and are expected to last at least until Tuesday evening in Ventura, Los Angeles and Santa Barbara counties, according to KABC, ABC News' Los Angeles station.

The extreme heat is forcing firefighters to work extra hard to combat large fires raging across New Mexico, Arizona and California.

Officials say the Dog Head Fire in New Mexico has already burned nearly 18,000 acres; only 9 percent of the fire was contained as of Sunday night.

Fire crews were able to control 40 percent of the Cedar Fire in Arizona which has burned more than 12,000 acres as of Sunday afternoon.

Sherpa Fire in California has burned nearly 8,000 acres as of Monday morning.

The record heat also impacted some flights over the weekend.

A United Airlines flight operated by Mesa Airlines departed Houston's George Bush Intercontinental Airport Sunday afternoon and was minutes away from landing at Sky Harbor Airport in Phoenix when the flight crew notified passengers it would be turning back due to the weather.

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