Amr Alfiky/Reuters
A person hides under a face cover in Manhattan's Central Park during a heat wave in New York on Friday, July 28.
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A construction worker drinks cold water during a heat wave where temperatures have reached over 110 degrees Fahrenheit for 27 consecutive days in Scottsdale, Arizona, on July 28.
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People keep cool in a fountain at New York's Battery Park on Thursday, July 27.
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Yemichael Abebe uses an umbrella to take shelter from the sun while waiting for a bus in Takoma Park, Maryland, on July 27.
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City workers take a break in the shade of a nearby storefront as they lay down new pavement in Woodland Hills, California, on July 27.
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A woman shades herself from the sun along the Brooklyn Bridge in New York on July 27.
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Vendors sell cold drinks near the Lincoln Memorial in Washington, DC, on July 27.
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Snickers, a great horned owl, is sprayed down with water by a volunteer at Liberty Wildlife, an animal rehabilitation center and hospital in Phoenix, on Wednesday, July 26.
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Representatives of the Miami-Dade County Homeless Trust distribute shelter information and bottles of water to people in Miami on July 25.
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Rick White drinks water while cooling down in his tent in "The Zone," Phoenix's largest homeless encampment, on Tuesday, July 25.
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A cactus in Phoenix is affected by the extreme heat and drought. Record-high temperatures in Arizona, combined with a lack of seasonal monsoons, have caused saguaro cactuses at the Desert Botanical Garden to become "highly stressed," according to Chief Science Officer Kimberlie McCue.
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Israel Sanchez, left, and Alfonso Garcia carry a person onto a stretcher in Eagle Pass, Texas, on July 18. The person, who was suffering from dehydration, fell sick after he and his mother were found with a group of migrants who recently crossed the Rio Grande into the United States.
Adriana Zehbrauskas/The New York Times/Redux
Roberto Guerrero, left, and his son Jose work in the early morning to install a new air conditioner at a home in Phoenix on July 18. Guerrero is part of perhaps the most essential workforce in town: AC repair techs. "If they need us, we go," he said of the long work hours.
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A person covers their head while trying to stay cool in "The Zone," a vast homeless encampment where hundreds of people reside in Phoenix, on July 18.
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Workers harvest onions overnight in Salem, New Mexico, to avoid working in the heat of the day on July 18.
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A man in Las Vegas puts his head in misters to cool off on July 17.
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A heat advisory sign is shown along Highway 190 at Death Valley National Park in Death Valley, California, on July 16.
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People sit in a crowded room at Phoenix's Justa Center, one of the area's many cooling centers, on July 16.
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A sign warning of extreme heat invites people to "Chill with Jesus" inside a church in Tucson, Arizona, on July 15.
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A firefighter watches flames from the Rabbit Fire approach Gilman Springs Road in Moreno Valley, California, on July 14.
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A person seeking shelter from the heat watches the weather forecast at the First Congregational United Church of Christ in Phoenix on July 14.
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Capt. Darren Noak, a medic with Austin-Travis County Emergency Medical Services, applies a chemical ice pack to a man in Austin, Texas, on July 12.
Richard Ellis/Zuma
A person fishes in Isle of Palms, South Carolina, on July 12.
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A sleeping child is protected from the sun in Los Angeles on July 12.
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A sign displays the temperature on July 12 as jets taxi at Phoenix's Sky Harbor International Airport.
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Kristin Peterson cools off with a cold bandana at the Sunrise Homeless Navigation Center in Austin on July 11.
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The "World's Tallest Thermometer" shows temperatures reaching triple digits in Baker, California, on July 11.
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Steven Rodriguez picks okra in Coachella, California, on July 11.
CNN  — 

An already dangerous weekslong heat wave will only worsen this weekend as a heat dome intensifies and reaches peak strength over parts of the Western United States.

The heat dome is so formidable the National Weather Service in Phoenix called it “one of the strongest high pressure systems this region has ever seen.” Around 100 heat records could fall today through the weekend as it intensifies, piling onto the more than 1,000 high temperature records broken in the US since June.

03:24 - Source: CNN
This is what happens to your body when temperatures soar

More than 90 million people are under heat alerts after the heat dome expanded into places like California, which is now experiencing its first extreme heat wave of the year.

It has already been dangerously hot for weeks in Texas, Florida and Arizona, where Phoenix is in the middle of a likely record-breaking streak of consecutive 110-degree days, forcing many businesses and parks to close or readjust their hours. The low temperature in Phoenix might not drop below 90 degrees for eight consecutive days, another record.

This shows how hot areas are compared to average with darker shades indicating more extreme heat.

The heat will be so intense, forecasters suggested residents of Las Vegas avoid the outdoors between 9 a.m. and 6 p.m., with the city forecast to challenge its all-time high temperature of 117 degrees on Sunday. It won’t get much cooler at night, with low temperatures nearing 90 degrees – a particularly dangerous side effect of the climate crisis.

Even the hottest place on Earth, California’s Death Valley, could reach rare highs, with 130 degrees possible Sunday, forecasters at the National Weather Service told CNN. It has only happened a handful of times, one of which is the all-time global record high temperature of 134 degrees.

In turn, Death Valley National Park in California and Saguaro National Park in Arizona posted warnings on their websites advising people not hike after 10 a.m. local time.

Officials at New Mexico’s White Sands National Park cautioned,”High temperatures over 100F degrees are expected. We strongly recommend to not start a hike if the temperature is over 85F degrees.”

Also, Texas authorities at Big Bend National Park said temperatures top 110 degrees daily along the Rio Grande river and throughout the desert areas.

“These are extremely dangerous/deadly temperatures! Hikers should be OFF TRAILS in the afternoon. Stay hydrated. Limit your exposure,” the park said on its website.

This kind of extreme heat is one of the hallmarks of human-caused climate change, the symptoms of which are tallying up this year into a global record box score of sorts: “unprecedented” ocean heat off the coast of Florida and in the North Atlantic; record heat in Beijing, in what could be one of the hottest summers in China; record energy demand and heat in Texas; and an ongoing “Cerberus” heat wave, threatening to topple European temperature records.

It all adds up to what could be the hottest year on record.

Businesses, parks close as temperatures climb

Skyrocketing temperatures across the western US have forced some businesses and parks to close or change their hours, such as the Sacramento Zoo, which shortened its hours due to the heat, closing early Friday, Saturday and Sunday at 1 p.m. PT as temperatures are forecast to reach 109 degrees Fahrenheit this weekend.

In Bakersfield, California, where the highest temperature this weekend is set to reach 114 degrees Fahrenheit, the Kern County Museum announced it would be closed “due to extreme heat” this weekend, according to a museum social media post. In Southern California, the Cleveland National Forest announced on its Facebook page that four of its trails – the San Diego River Gorge, Cedar Creek Falls, Three Sisters Falls and Eagle Peak – will be closed through the weekend due to “excessive heat.”

Other businesses in California, such as the California Gray’s Flower Garden in Quincy and the Nascere Vineyards in Chico announced plans to close their doors over the weekend as temperatures are expected to reach over 100 degrees Fahrenheit.

The Bison Café in Quitaque, Texas said it was limiting its hours due to higher temperatures that are making the kitchen “very uncomfortable” for cooks.

Separately, in Phoenix, the Arizona Animal Welfare League decided to close its doors for the weekend. “The safety of our pets is our top priority and with temperatures expected to hit over 115, our staff’s main focus will be on keeping our animals cool and comfortable during this time,” a Facebook post from the organization reads.

A ‘perfect storm’ of deadly heat

The records also add up into something more serious for human health, doctors say.

“Make no mistake about it: This heat is deadly, and being in it for long periods of time is deadly,” Dr. Matthew Levy of the Johns Hopkins University School of Medicine told CNN.

The extreme temperatures could trigger heat illness in as little as 20 to 30 minutes for people doing anything strenuous outdoors, because heat acts as a “perfect storm,” which overloads the body until it eventually short-circuits and then shuts down, Levy said. The time frame would be even shorter for those most vulnerable to heat, like the elderly and those with preexisting health conditions.

Heat illness is a serious concern this weekend for the millions of residents in major metro areas like Phoenix and Las Vegas.

People across the Southwest and California’s Central Valley are under a rare “extreme” level of heat risk on Saturday, Sunday and Monday, according to the weather service.

The “extreme HeatRisk” is the highest possible risk level for heat, akin to a “high risk” for tornadoes, and is meant to warn of significant heat impacts requiring preparation.

These areas should prepare for spikes in heat-related ER visits, potential power outages from demand and temperatures high enough to turn deadly, especially for outdoor workers and those without reliable cooling.

Levy said workers can stay safe by taking frequent hydration breaks, wearing clothing able to reflect the sun and having a “buddy system” so no one is left in the heat alone when illness strikes. For those who don’t have reliable cooling, he recommends finding a cooling center and having a plan to get there before the need arises.

All of the areas shaded in red will exceed 90 degrees on Saturday.

Before the latest wave, heat has already killed at least 12 people in Phoenix’s Maricopa County this year, and killed 425 people last year. The city has opened “respite centers” to help provide relief and the state has asked residents to keep their vehicles stocked with water.

The heat won’t go away after this weekend, even if temperatures peak: Longer term temperature outlooks from the Climate Prediction Center point to above normal temperatures across Southern California, the Southwest, South and Florida through next week.

CNN’s Dave Alsup contributed to this report.