Heat wave roasts southwestern U.S.

Phoenix authorities issued several warnings about the dangers of the heat. Phoenix park ranger Chris Webb said she saw about a dozen hikers on Camelback Mountain in the afternoon hours.

“I would recommend that people do something less strenuous than to come out to the toughest hike in Phoenix in the middle part of the day,” she said. “Maybe go swimming. Maybe do something indoors instead.”

The first day of summer brought some of the worst heat the southwestern U.S. region has seen in years.

Meteorologists said Tuesday’s temperature in Phoenix topped out at 119 degrees, a mark that’s only been matched or surpassed four other times in the city’s recorded history. The all-time high was 122 degrees on June 26, 1990.

Death Valley, California, reached 125 Tuesday and Palm Springs hit 121, still a degree lower than the same day last year.

The heat wave comes amid new research findings that nearly 1 in 3 people now experience 20 days a year when the heat reaches deadly levels.

The study of nearly 2,000 deadly heat waves worldwide since 1980 was published Monday in the journal Nature Climate Change.

Workers at a construction site in a Phoenix suburb huddled under the shade of an excavator during a break. At another building site, men in hard hats and yellow vests laboured and sweated in the heat, downing water to stay hydrated.

Las Vegas also baked. Visitors tried to stay inside air-conditioned casinos, and some tourists lugged packs of bottled water around the Strip. Others went to a bar where the temperature is set at 23 degrees (-5 Celsius) and glasses, walls and seats are sculpted from ice. (AP)

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Heat wave roasts southwestern U.S.

A pedestrian uses an umbrella to get some relief from the sun as she walks past a sign displaying the temperature on June 20, 2017 in Phoenix, Arizona. Record temperatures of 118 to 120 degrees were expected on Tuesday for the Phoenix-metro area. (Ralph Freso/Getty Images)

Heat wave roasts southwestern U.S.

A young boy finds some relief from the heat under a cascading waterfall feature at the Wet-N-Wild Water Park on June 20, 2017 in Phoenix, Arizona. (Ralph Freso/Getty Images)

Heat wave roasts southwestern U.S.

Thirty-three year old Eric Maurice Clark sells cold bottled drinks to drivers at a busy intersection on June 20, 2017 in Phoenix, Arizona. Record temperatures of 118 to 120 degrees were expected on Tuesday for the Phoenix-metro area. (Ralph Freso/Getty Images)

Heat wave roasts southwestern U.S.

Jennifer Boushy, left, and Jennifer Rellinger, right, cool off their dogs in water at a dog park, June 20, 2017, in Las Vegas. The first day of summer is forecast to bring some of the worst heat the southwestern U.S. has seen in years. (John Locher/AP)

Heat wave roasts southwestern U.S.

Heat waves ripple across the tarmac at Sky Harbor International Airport as downtown Phoenix stands in the background as an airplane lands, June 20, 2017 in Phoenix. Phoenix hit a high of 118 on Monday with an excessive heat warning in place until Saturday. (Matt York/AP)

Heat wave roasts southwestern U.S.

Crew members building the Loop 202 South Mountain Freeway take a break as they try to keep hydrated and stay cool as temperatures climb to near-record highs, June 20, 2017, in Phoenix. (Ross D. Franklin/AP)

Heat wave roasts southwestern U.S.

Morgan Reed, a promotions assistant for KSLX, plays with a puppy wearing elastic booties at a PetSmart in Tempe, Ariz. on Tuesday, June 20, 2017. (Angie Wang/AP)

Heat wave roasts southwestern U.S.

Xaviere Coleman pours water over his head to cool off in a Wookiee costume along the Las Vegas Strip, June 20, 2017, in Las Vegas. Coleman was taking a break from posing for photographs with tourists. (John Locher/AP)

Heat wave roasts southwestern U.S.

One person uses the CityScape splash pad to stay cool as temperatures climb to near-record highs, June 20, 2017, in Phoenix. (Ross D. Franklin/AP)

Heat wave roasts southwestern U.S.

A local temperature sign reads 120-degrees as temperatures climb to near-record highs, June 20, 2017, in Phoenix. (Ross D. Franklin/AP)

Heat wave roasts southwestern U.S.

People cross Las Vegas Boulevard as the sun beats down, June 20, 2017, in Las Vegas. (John Locher/AP)

Heat wave roasts southwestern U.S.

Chris Mitchell sprays water on his face to cool off in a Darth Vader costume along the Las Vegas Strip, June 20, 2017, in Las Vegas. (John Locher/AP)

Heat wave roasts southwestern U.S.

A Salvation Army hydration station sign gets hit by the midday sun as temperatures climb to near-record highs, June 19, 2017, in Phoenix. (Ross D. Franklin/AP)

Heat wave roasts southwestern U.S.

Steve Smith wipes sweat from his face as temperatures climb to near-record highs in Phoenix on June 19, 2017. (Ross D. Franklin/AP)

Heat wave roasts southwestern U.S.

Urijah Salcedo throws a bucket of water on himself while playing in Spring Valley Lake in Victorville Calif., June 19, 2017. (James Quigg/The Daily Press via AP)

Heat wave roasts southwestern U.S.

Jai, a Sumatran Tiger, sits in a pool to keep cool at the Phoenix Zoo, June 19, 2017 in Phoenix, Ariz. (Matt York/AP)

Heat wave roasts southwestern U.S.

Salvation Army volunteers Evangeline Ford, left, and Jackie Rifkin, right, restock a cooler with bottles of water at a hydration station for people as they try to keep hydrated and stay cool as temperatures climb to near-record highs, June 19, 2017, in Phoenix. (Ross D. Franklin/AP)

Heat wave roasts southwestern U.S.

Lori Mantz sprays water to cool down her horse Thor, June 19, 2017, in Las Vegas. (John Locher/AP)

Heat wave roasts southwestern U.S.

An American Eagle jet is seen through heat ripples as it lands at Sky Harbor International Airport, June 19, 2017,in Phoenix. (Matt York/AP)

Heat wave roasts southwestern U.S.

Carolina Colon tosses a shark water toy airborne while cooling off at Spring Valley Lake in Victorville Calif., June 19, 2017. (James Quigg/The Daily Press via AP)

Heat wave roasts southwestern U.S.

Lori Mantz sprays water to cool down her horse Chavi, June 19, 2017, in Las Vegas. (John Locher/AP)

Heat wave roasts southwestern U.S.

A man stands under a misting machine, June 19, 2017 in Tempe, Ariz. The forecast calls for a high of 118 on Monday and 120 on Tuesday in Phoenix. (Matt York/AP)

Heat wave roasts southwestern U.S.

The late afternoon temperature hits 115-degrees in downtown Phoenix, June 19, 2017. (Ross D. Franklin/AP)

Heat wave roasts southwestern U.S.

A woman walks along a row of misters, June 19, 2017 in Tempe, Ariz. (Matt York/AP)

Heat wave roasts southwestern U.S.

An owl is hosed off to keep cool at the Phoenix Zoo, June 19, 2017 in Phoenix, Ariz. (Matt York/AP)

Heat wave roasts southwestern U.S.

Loulou, a white rhinoceros, buries here horn in the mud to keep cool at the Phoenix Zoo, June 19, 2017, in Phoenix, Ariz. (Matt York/AP)

Heat wave roasts southwestern U.S.

A man runs through the desert at sunrise, June 16, 2017, in Phoenix. (Matt York/AP)

Heat wave roasts southwestern U.S.

A man walks through a mister during the start of a heat wave in Las Vegas, June 16, 2017. (John Locher/AP)

Heat wave roasts southwestern U.S.

Blake Shetley grins as he’s doused with water from a fountain in Spring Valley Lake in Victorville Calif., June 19, 2017. (James Quigg/The Daily Press via AP)

Heat wave roasts southwestern U.S.

Alan Schwandt, an air conditioning repairman, removes his hat and glasses to wipe sweat from his face while examining a rooftop unit in Scottsdale, Ariz., June 19, 2017. (Angie Wang/AP)

Heat wave roasts southwestern U.S.

Hikers brave the afternoon sun as the temperatures hit 110-degrees June 15, 2017, in Phoenix. (Ross D. Franklin/AP)