Record-Breaking Heat Wave Expected to Ease in Much of the U.S.

The unusually early heat wave that shattered temperature records across the Northeast, Mid-Atlantic States and Midwest last week is expected to subside by Monday, bringing relief to tens of millions of Americans.

The National Weather Service forecast lower temperatures for much of the Mid-Atlantic on Monday.

In Washington, the heat index — a measure of how conditions feel, with humidity taken into consideration — is expected to reach a high of 87 degrees, down from 102 on Sunday. Philadelphia is also expected to have a much lower heat index value, at 82 degrees, down from 104 on Sunday, forecasters say. And in Trenton, N.J. — the capital of the state, which climate experts say is warming faster than others in the region — the figure is expected to come down to 82, from 103 on Sunday.

The forecast is welcome news along the Interstate 95 urban corridor on the East Coast, where residents faced especially stifling conditions over the weekend. Places like Baltimore and Dulles, Va., broke daily temperature records two days in a row.

But regions in the Southeast and Southern Plains are expected this week to remain hot — possibly at dangerous levels — with potential highs in the low 100s, according to the Weather Service. Parts of Kansas, Oklahoma, Arkansas, Mississippi, Alabama, Georgia and Florida are forecast to face extreme risks from heat on Tuesday, the service said, taking into account both the weather conditions and how unusual they are for the time of year.

At the heat wave’s peak extent last Thursday, nearly 120 million people were under heat advisory alerts from the Weather Service, and the number of people under such advisories remained above 100 million for at least four days straight.

More than the heat itself, its early arrival shocked some Americans.

“I hoped the weatherman was mistaken,” said Shenay Smith, a 44-year-old wine tasting technician in New Castle, Del., where the heat index soared to 107 on Sunday. “Unfortunately, not this time,” she added.

For many, it was a brutal start to a summer that promises to be punishing: According to the National Oceanic and Atmospheric Administration, 2024 is on track to be among the five hottest years on record, and there’s a 50 percent chance it will be the warmest ever.

Climate change is driving more severe extreme heat events around the world, scientists say. In recent years, global warming has made heat waves hotter, more frequent and longer. Daily temperature records were broken in dozens of cities, including Boston, Pittsburgh, Baltimore and Chicago, during this heat wave.

The health consequences of this heat wave have shown up in some data and anecdotes: Heat-related illnesses spiked in parts of New England, the Midwest and the Mid-Atlantic last week, according to data from the Centers for Disease Control and Prevention’s heat and health tracker.

In Philadelphia, the heatline — which directs people struggling to handle the heat to cooling centers and medical attention, if necessary — received more emergency calls than usual, according to Nolan Lawrence, the director of its helpline for seniors.

“It’s particularly brutal out here the last few days,” Mr. Lawrence said on Sunday, as temperatures in Philadelphia broke the daily record set in 1888.

But not everyone was too bothered by the heat.

Lafayette Collins, a 44-year-old mortgage loan broker, brought his three sons to watch a minor league baseball game between the Aberdeen IronBirds and the Wilmington Blue Rocks in Wilmington, Del., on Sunday. Braving triple-digit heat index figures, Mr. Collins and his sons came to Frawley Stadium prepared with umbrellas to fend off the sun and a plastic bag stuffed with towels soaked in water.

“What’s the alternative?” Mr. Collins asked.

Stacy M. Brown contributed reporting.