Heat dome brings potentially historic temperatures to most of the nation

The Northeast and Midwest, including New York City and Boston, are bracing for what could be the hottest stretch of weather in 30 years this week as a sweltering heat dome settles over a large part of the nation.

Over the next six days, 265 million people, or about 82% of the U.S. population, are likely to experience temperatures topping 90 degrees as the official first day of summer arrives on Thursday.

Many cities in the Midwest and the Northeast could experience what the National Weather Services calls rare and long-duration heat with up to five straight days of 95-plus-degree weather with high humidity that will make it feel 100 to 105 degrees.

As of Monday morning, 17 states from Iowa to Maine were under a heat alert. An Excessive Heat Watch was already issued Sunday for parts of New England, including Connecticut, Massachusetts and New Hampshire. The temperature in Concord, New Hampshire, is forecast to reach 101 on Wednesday.

PHOTO: Spectators stand in the heat while waiting to watch players warm up prior to an international soccer friendly between Mexico and Brazil on June 8, 2024, at Texas A&M's Kyle Field in College Station, Texas. (Julio Cortez/AP)
PHOTO: Spectators stand in the heat while waiting to watch players warm up prior to an international soccer friendly between Mexico and Brazil on June 8, 2024, at Texas A&M's Kyle Field in College Station, Texas. (Julio Cortez/AP)

The Ohio Valley could experience the most impactful heat wave of the 21st century. Louisville, Kentucky, is forecast to hit 94 degrees on Wednesday, 97 on Thursday and 99 on Friday.

New York City could feel its first heat wave of the year as temperatures are forecast to reach 91 degrees on Wednesday and 94 on Thursday and 96 on Friday.

New York City Mayor Eric Adams said at a news conference Monday morning that he expects the National Weather Service to issue a heat advisory for the nation's largest city on Thursday and Friday. He said the city will open cooling centers on Tuesday.

"We expect to hit peak heat on Thursday and Friday with the heat index possibly reaching 99 degrees," Adams said. "We want to be clear, this is extremely hot for June and New Yorkers should not underestimate the heat."

Pittsburgh is also in for a string of hot weather with temperatures expected to soar from 97 degrees on Tuesday and Wednesday to 98 degrees on Thursday and Friday.

PHOTO: Kids play in a splash pad at Riverview Park on June 05, 2024 in Mesa, Ariz. (Justin Sullivan/Getty Images)
PHOTO: Kids play in a splash pad at Riverview Park on June 05, 2024 in Mesa, Ariz. (Justin Sullivan/Getty Images)

The heat-wave forecast for Pittsburgh could be the city's hottest all-time for the month of June. The previous five-day June record occurred in 1994 with a temperature average of 96.4 degrees.

MORE: Severe weather hits northern Plains as major heat wave set to move across country

The all-time record for a heat wave in Pittsburgh happened in mid-July 1988 when city residents sweltered for five consecutive days with 98.6-degree temperatures.

PHOTO: Dangerous heat wave this week. (ABC News)
PHOTO: Dangerous heat wave this week. (ABC News)

Washington, D.C., is also expected to be inundated with 90-degree weather and could flirt with the century mark by Friday.

High temperatures are also forecast for Ohio and southeast Michigan, where an excessive heat watch is also in effect from Monday through Friday.

Daily temperature records are expected to fall this week in Chicago, Green Bay, Cleveland and Toledo.

Upstate New York could also see daily heat records fall. In Rochester, temperatures on Monday are forecast to hit 94 degrees, which would tie a daily record. Syracuse is also forecast to reach 94 degrees on Monday, which would break a daily record.

PHOTO: Heat wave Monday's temperatures. (ABC News)
PHOTO: Heat wave Monday's temperatures. (ABC News)

Out west, dangerous heat is expected for Texas, Arizona, Nevada and New Mexico.

MORE: More flooding in the forecast after more than 2 feet of rain inundates South Florida

An excessive heat warning was issued for Phoenix and Tucson, Arizona, where temperatures threatened to hit the 110-degree mark on Sunday.

PHOTO: Heat risk weather map for Tuesday, June 18. (ABC News)
PHOTO: Heat risk weather map for Tuesday, June 18. (ABC News)

Roswell, New Mexico, is expected to reach 105 degrees on Sunday and El Paso and Fort Stockton, Texas, are expected to get just as warm.

PHOTO: Heat risk weather map for Thursday, June 20. (ABC News)
PHOTO: Heat risk weather map for Thursday, June 20. (ABC News)

Authorities warn people enduring such high temperatures to stay hydrated and out of the heat, and to check on elderly neighbors and relatives.

In 2023, there were 2,302 heart-related deaths across the country, a 34% increase from 2022.

Heat dome brings potentially historic temperatures to most of the nation originally appeared on abcnews.go.com

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