NEW YORK CITY >> U.S. cities are breaking decades-old temperature records this week as a heat wave stretches from central to eastern portions of the country, the National Weather Service said today, in what officials are warning could become a deadly weather event.

With roughly 80 million people from Indiana to New England under a heat advisory or excessive heat warning, New York Governor Kathy Hochul activated the state’s Emergency Operations Center in response to high temperatures expected to last until the weekend.

“This is a deadly event,” she said, one day after the city of Syracuse hit 94 degrees Fahrenheit, topping a record from 1994. “We have seen blizzards, we have seen flooding, we had hurricanes, we had tornadoes. But this heat event is most likely to cause more deaths.”

As the heat wave began even before the official start of summer on Thursday, New York’s beaches and public pools will open early, in time for people to enjoy them over the Juneteenth holiday on Wednesday, she said.

“A heat wave can be more than just uncomfortable. It can be deadly and life-threatening if you are not prepared,” said New York City Mayor Eric Adams.

Under its heat emergency plan, New York City is opening its cooling centers for the first time this year.

In Chicago, teams of city workers scattered across the city to homeless camps, trying to coax people to escape the heat in shelters, said Brian Berg, a spokesperson for the city’s Department of Family Services and Support.

“We check all the sites,” Berg said. “We provide them with not only water and food, but we’ll take them to the shelters, which are also cooling stations.”

Chicago registered 97 degrees F at Chicago O’Hare International Airport on Monday, which broke a record of 96 degrees F set in 1957. The heat index, which factors in temperature and humidity to measure how hot it feels, touched 105 degrees F on Monday.

High temperatures can cause dehydration, heat exhaustion and heatstroke, and worsen pre-existing conditions like cardiovascular problems.

Detroit and Philadelphia, as well as cities in New Hampshire, Connecticut and Maine are also due for record temperatures in the coming days, NWS meteorologist Marc Chenard said.

While it is too soon to say if the heat is driven by climate change, this wave is occurring earlier in the year than the historical average. Central Maine is running 30 degrees above average, he added.

“It’s kind of early in the season to be getting this long of a duration of heat wave for the Ohio Valley and New England,” Chenard said, adding that it was dangerous because people were not prepared.