School is about to start, pumpkin-spice coffee is back on the menu, and New York City’s public pools close for the season in less than a week, but city residents are encountering some of the most sweltering heat of the year.

Temperatures in New York City climbed into the mid-90s on Tuesday — unusual after Labor Day, according to Dave Radell, a National Weather Service meteorologist in New York — and were expected to reach similar heights on Wednesday and Thursday. The National Weather Service issued a heat advisory for New York City until 8 p.m. on Thursday.

Some places in the surrounding area experienced the hottest Sept. 5 on record, Mr. Radell said, including Newark, where the temperature reached 95 degrees, and the town of Islip on Long Island, which hit 91. Both broke records that had been in place since 1985.

It has been decades since the area around New York City had a September with three consecutive days with temperatures over 90 degrees, Mr. Radell noted, though he said there was not currently evidence to suggest that such heat at this time of year would become common.

Con Edison said its crews were preparing to respond to potential power outages and urged New Yorkers to limit the use of large appliances.

Jamie McShane, the company’s director of media relations, said that air-conditioners should be set to the highest comfortable temperature to help conserve energy and that window shades should be kept closed.

The city’s office of emergency management warned of the health risks posed by extreme heat and urged people who do not have reliable access to air-conditioning to take advantage of the city’s cooling centers, splash pads, public pools and other resources. Many New Yorkers did not have to be told twice.

At Domino Park in Williamsburg, Miki Rudick, 45, and Mary Healing, 41, of Bushwick, sat for several hours by the East River while their 5-year-old daughters, Sonja and Moira, splashed in a fountain.

“I always find that September, I’m surprised by how hot and humid it is,” Ms. Healing said.

Ms. Rudick, who grew up in Israel, added that she often thinks about climate change and that it might be better for children to learn to tolerate the heat, because “it’s only going to get hotter for them.”

In Bushwick, Venus Demps, 64, sat on her walker outside St. Nicks Alliance Swinging Sixties Older Adult Care Center and waited for the ride that would take her back to her apartment in Flatbush. The St. Nicks site is one of the city’s cooling centers.

“I have air-conditioning, but you know, it’s only in one room,” she said. She could have stayed home, she said, but she enjoys going to the center, where she can socialize, be active and have lunch.

Some students at Barnard College in Manhattan had just moved into dorms without air-conditioning and were struggling to cope with the heat.

“Basically everybody is counting down the days until it goes away,” Emma Carter, an 18-year-old freshman, said.

Ms. Carter said that she and her roommate, Eden Stranahan, 18, had been taking cold showers, sometimes several times a day, and that it had been difficult to make their room in Brooks Hall — Barnard’s oldest dormitory — feel like home.

“Posters and stuff just melt off the wall,” Ms. Stranahan said.

In an email on Tuesday, the college advised students to use fans, cold washcloths and ice to bring down their body temperatures. “It might be tempting to sleep with your door open, but please keep it locked for your safety,” the email read.

At the U.S. Open in Queens, players and fans endured sweltering temperatures and oppressive humidity. Extreme weather policies were implemented for singles matches, the junior championship and the wheelchair championship, allowing more breaks and, in some cases, even suspending matches until the temperature dropped.

In an interview before her quarterfinal match against Jelena Ostapenko at Arthur Ashe Stadium, Coco Gauff said that training in South Florida had prepared her well for the day’s heat.

Another South Florida resident, Laura Walley, 62, a retiree from Pensacola who was viewing the tournament, also said she was no stranger to high heat and humidity but added that she wasn’t used to staying outside in such temperatures.

Sitting at a shaded table in the South Plaza of the U.S.T.A. Billie Jean King National Tennis Center, Ms. Walley said that she had attended the tournament every day since Sunday and that “each day got progressively hotter.”

She had made adjustments, she said: bringing frozen water bottles and wearing lighter clothing.

Louise Clarke, 50, and her husband, Alastair Clarke, said they had traveled from Sevenoaks, England, and were determined not to let the heat prevent them from enjoying the tournament.

A slight breeze passed through the trees in the South Plaza, and Mr. Clarke said he hoped it would continue throughout the day “so we don’t just sit and fry in the sunshine.”

“The players are out there in the heat, and they’ll put on a great show for us for sure,” he said.

Lola Fadulu, Hilary Howard, Olivia Bensimon and Eliza Fawcett contributed reporting.