A record-breaking heat wave with a combination of humidity and temperatures well into the 90s will descend on cities in the Midwest and Northeast this week in what is expected to be a dangerous weather system days before summer officially begins, forecasters said.

“The duration of this heat wave is notable and potentially the longest experienced in decades for some locations,” the National Weather Service said on social media on Sunday.

In Pennsylvania, temperatures in Philadelphia, Allentown and Reading are expected to reach 95 degrees or higher for five consecutive days, a streak that has not occurred since July 2022, August 1953 and July 2011, respectively, according to the Weather Service office in Mount Holly, N.J.

The severe heat was rapidly developing ahead of a low pressure system and spreading to the central Plains, Great Lakes region and Ohio Valley on Sunday, the Weather Service said.

High temperatures in Ohio on Sunday reached into the 80s, with humidity at fairly comfortable levels, but hot and humid conditions were expected through the week in Ohio and Pennsylvania, the Weather Service office in Cleveland said on social media.

The office said an excessive heat watch was in effect from Monday through Friday for areas that included Cleveland, Detroit, Pittsburgh and Erie, Pa., where temperatures could surge into the 90s during the day.