Peak temperatures from a potentially deadly heatwave are expected to begin Friday, and major US cities are taking special measures to prepare -- with New York City declaring an emergency.
Over the next few days, more than 85% of the lower 48's population will see temperatures above 90 degrees Fahrenheit, CNN meteorologist Dave Hennen said, and more than half will see temperatures higher than 95 degrees.
About 185 million people are under a heat watch, warning or advisory as of Friday morning.
The heat has the potential to break records and turn deadly as temperatures climb over the weekend all along the East Coast and through the Midwest.
High temperatures are expected to scorch the major cities of the East Coast.
Boston, Pittsburgh, New York, Baltimore and Washington are under excessive heat watches. Philadelphia is under an excessive heat warning, and in the southern end of the coast, Raleigh is under a heat advisory.
Mayor Bill de Blasio has declared "a local emergency due to the extreme heat" in New York City. In an executive order that covers 9 a.m. Friday to 11:59 p.m. Sunday, the mayor is ordering buildings 100 feet or taller to raise thermostats to 78 degrees in an effort to conserve energy.
"We are about to enter a heat emergency, and must do all we can to keep New Yorkers safe," said de Blasio. "The city government is limiting its energy use to reduce strain on the electrical grid, and now private office buildings will also have to do their part."
With extreme temperatures through Sunday, the Verizon New York City Triathlon has been canceled. The organization says it's not safe for the athletes or the spectators.
"After exhausting all options to mitigate athlete, volunteer, spectator and staff exposure alike, we are unable to provide either a safe event experience or an alternate race weekend," organizers announced in a press release. "As a result, in collaboration with the City of New York and all supporting agencies, Sunday's triathlon has been canceled."
Detroit is taking extra measures to make sure residents can get relief from the sweltering heat that is also expected in the Midwest.
In addition to cooling centers open on the weekdays, the city will open recreation centers on the weekend to give access to air-conditioning, according to a press release.
The mayor's office and the Detroit Police Department will also be checking on homeless people to offer them transport to cooling centers this weekend, the release said.
As cities all over the region -- such as Cleveland, Minneapolis, Chicago, Omaha and Detroit -- face heat warnings or advisories, Detroit officials are urging residents to drink plenty of water, reduce outdoor activities, eat light and check on family and neighbors.
Heat wave made worse by climate crisis
June of this year was the hottest June on record for the world, according to the National Oceanic and Atmospheric Administration . It isn't clear yet how July will fair in terms of breaking records, but temperatures for this week are high.
Experts say the heat wave is only made worse by the ongoing threat of climate change. According to last year's National Climate Assessment , the number of hot days in the US is increasing.
Heat waves have also increased in frequency, rising from an average of two per year to six per year in the last five decades. The threat is especially pronounced in the Northeast, where "the frequency, intensity, and duration of heat waves is expected to increase" due to the climate crisis.
By 2050, the Northeast can expect approximately 650 more deaths each year because of extreme heat, the assessment found.
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