US braces for massive heat wave, over 75 million remain under alert

The US is bracing for a massive week-long heat wave, weather experts have warned, according to media outlets.

The Northeast and Midwest are preparing for sweltering temperatures as a "heat dome" settles over a large part of the country.

The National Weather Service (NWS) said that over 75 million people were under some level of heat alert as of Monday morning. Some 150 million people will experience temperatures above 32C, and 9 million people could see readings rise over 37.7C.

Over the next six days, 265 million people — about 82 percent of the US population — are likely to experience temperatures topping 32C as the official first day of summer begins on Thursday.

"Potentially dangerous heat is expected for much of the week," said the NWS Indianapolis division, where the state of Indiana is under an excessive heat warning.

New York City is preparing for the hottest period of weather in 30 years, with temperatures reaching 32.7C on Wednesday, 34C on Thursday and 35C on Friday.

The city will begin opening 500 cooling centres for residents, with a heat advisory expected to be issued by the NWS.

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

New heat records

As of Monday, 17 states were already under a heat alert, with Excessive Heat Watches being issued for the states of Connecticut, Massachusetts and New Hampshire, where the city of Concord is forecast to hit 38C on Wednesday.

"By Wednesday afternoon, some locations in interior New England could see temperatures topping the century mark, which will break daily records at certain locations," said the NWS.

Weather officials said the Ohio Valley could experience the most impactful heat wave of the 21st century, with Louisville, Kentucky, expected to hit 34C on Wednesday, 36C on Thursday and 37C on Friday.

Pittsburgh, Pennsylvania is also bracing for a string of excessive heat, with temperatures expected to soar from 36C on Tuesday and Wednesday to 36.6C on Thursday and Friday.

The heat wave could be the city's hottest of all time for the month of June. "Now that we're closing in on the heat wave, the Watch has turned into a Heat Advisory," the NWS Pittsburgh division said in a statement.

"Please take precautions if you're outside this week and check on those that are most vulnerable."

Dangerous heat is also expected for Arizona, where the cities of Phoenix and Tucson are under Excessive Heat Warnings, with temperatures expected to peak at 43C on Sunday.

Roswell, New Mexico and El Paso, Texas, are forecast to reach 40.5C.

Authorities are warning people to take precautions, including staying indoors when possible, staying hydrated and checking on elderly neighbours and relatives.

There were 2,302 heart-related deaths across the US in 2023, a 34 percent increase from 2022.

The National Weather Service said new heat records could be set in some 200 cities across the US during this week-long heat wave.

Late-season snow

While much of the US swelters, late-season snow was forecast for the northern Rockies on Monday and Tuesday.

Parts of Montana and north-central Idaho were under a winter storm warning.

As much as 51 centimetres was predicted for higher elevations around Glacier National Park.

Meanwhile, a fresh batch of tropical moisture was bringing an increasing threat of heavy rain and flash flooding to the central Gulf Coast.

Hurricane season this year is forecast to be among the most active in recent memory.