Phoenix's dry heat became a deadly heat Thursday as the National Weather Service issued an excessive heat warning for the area, with temperatures projected to hit 114 degrees, the highest of the year so far.
The warning extended into other parts of Arizona and California.
The service said the warning will run through Friday evening as the risk rises for potentially fatal heat-related illnesses such as heat stroke and heat exhaustion for people spending time outside in the broiling sun. Afternoon hours will be especially dangerous, the agency said.
The excessive heat warning extended to parts of southwestern Arizona, including Casa Grande, Tucson, Gila Bend and Yuma. It also spread into areas of southeastern California, including Blythe, Coachella, Indio and Palm Springs.
"It looks like Thursday will be the hottest year of the day so far," agency forecaster Marvin Percha said. "But it can get hotter than this."
The weather agency uses a complicated formula that varies from region to region to declare an excessive heat warning, including close to record-breaking temperatures.
"The record for today is 116," Percha said. "We're looking for a bit cooler on Friday, maybe 111 (43.8 Celsius). Our main concern is that people stay safe."
Forecasters recommended that people stay home on Thursday and Friday or seek shelter in air-conditioned public places such as libraries, community centers, shopping malls, as well as special cooling and hydrating stations.
There were 155 heat-associated deaths in Phoenix's Maricopa County in 2017, the highest annual number ever recorded, as the city experienced its warmest year on record.
According to the Arizona Department of Health Services, 219 people died from heat-associated causes around the state last year, with nearly 1,300 heat-caused deaths statewide during the decade from 2005 to 2015.
Maricopa County has reported only two heat-related deaths so far in 2018, said Scott Johnson, Southwest public relations director for the Salvation Army, which operates 13 cooling stations in the Valley of the Sun. The Maricopa County of Governments operates dozens more at libraries, churches and senior centers, helping people get out of the sun, drink water and rest in an air-conditioned area.
"That low number is amazing," Johnson said. "I'd like to think that means that the word is getting out about the stations."
Amid the heat wave, Arizona's Department of Transportation issued its own warning to travelers, recommending that people leaving on road trips bring fully charged cellphones, extra drinking water for themselves, passengers and pets and an umbrella for shade outside the vehicle.
It also suggested that gas tanks be kept at least three-quarters full.
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