Residents around the Northeast U.S. braced for potentially record-breaking temperatures Sunday as a nearly weeklong hot spell continued, prompting officials to warn of “dangerous” heat.

At least one heat-related death, in New York, was reported during the stretch of sweltering weather. Around the region, athletic events were shortened or postponed, and cities opened cooling centers and even turned to buses to offer relief from the heat.

From the Pacific Northwest to the southern Great Plains to the heavily populated I-95 corridor, more than 85 million Americans woke up Sunday to excessive heat warnings or heat advisories, the National Weather Service said. Much of the heat was in the Northeast, where the weather service warned of “extremely oppressive” conditions from Washington to Boston.

“Numerous records highs are forecast to be tied and/or broken today in the Northeast as highs make a run at the century mark” and humidity makes it feel as hot as 105 to 110 degrees Fahrenheit (40.5 to 43 degrees Celsius), the weather service said in a forecast discussion.

Philadelphia was forecast to hit 100 degrees (38 Celsius) before even factoring in humidity, said weather service meteorologist Matt Brudy in Mount Holly, N.J.

Philadelphia officials extended a heat health emergency declaration through Sunday, sending workers to check on homeless people and knock on the doors of other vulnerable residents. With Health Commissioner Dr. Cheryl Bettigole calling the weather “dangerously hot,” the city also opened cooling centers and stationed air-conditioned buses at four intersections for people to cool off.

Forecasters urged people to take precautions, wear light clothing, drink lots of water, limit time outside and check on elderly people and pets.

New York City medical examiners confirmed Sunday that a person had died of heat-related causes but didn’t say when or where. The person had heart disease and emphysema, which contributed to the death, the medical examiner’s office said.

With the city expected to approach its record high of 97 degrees (36 Celsius) for Sunday’s date, organizers of the New York City Triathlon shortened the distances that athletes had to run and bike. The bicycle leg was cut in half to 20 kilometers (12.4 miles).

This weekend’s Boston Triathlon, meanwhile, was put off until Aug. 20-21. Temperatures were expected to reach the upper 90s in Boston on Sunday, according to the National Weather Service.