Drawn-Out Heat Wave Expected to Finally Let Up in Many Parts 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.