Summer heat isn't over: Heat wave hits 70+ million people in NYC, other major cities

A record-breaking September heat wave is stifling portions of the nation Thursday, with forecasters imploring residents planning to spend time outdoors to hydrate and avoid strenuous activity.

Scorching temperatures are expected to linger through Friday in the Mid-Atlantic and Northeast and through the weekend in Texas and adjacent states, the National Weather Service said.

The agency issued a heat advisory Thursday affecting nearly 60 million people in major population centers of the northeast from Philadelphia to near Boston and into upstate New York as well as throughout east and west Texas, northern Louisiana, southern Arkansas and southern Mississippi.

The weather service also called for excessive heat warnings in central Texas, southeast California and southern Arizona – including Phoenix, where temperatures are expected to soar to 110 degrees and above this weekend. Almost 16 million people live where an excessive heat warning is in effect as of midday Thursday.

In San Antonio, Texas, Wednesday marked the 70th day of 100-degree temperatures or above since June, marking an all-time record for the area. The forecast high for Thursday in San Antonio was 103 degrees.

Already this week, schools across the Mid-Atlantic and Northeast have closed or sent students home early because of record-breaking temperatures as much as 10 degrees above normal. Across the nation, some public schools are struggling to find funding to install or upgrade cooling systems.

In Massachusetts, one high school rescheduled football practices to 5:30 a.m. in an effort to beat the heat. Meanwhile, officials in several state school districts announced they would close schools early or entirely on Thursday, including Framingham Public Schools, where all Thursday afternoon and evening activities were cancelled.

"We understand that early dismissals can be hard for working caregivers," administrators said in a posting on the district website. "While some of our school learning environments are equipped with air conditioning, some are still works in progress."

This article originally appeared on USA TODAY: Sweltering heat forecast by NWS for 70+ million in US: What to know