A heat wave is expected to settle over New York City this week, as city officials grapple with how to keep construction workers, street vendors and others who work outdoors safe as summers in the city grow warmer.

By Wednesday, according to National Weather Service forecasts, highs could jump to 97 degrees. By Thursday, the temperature is expected to hit 100 degrees, climbing as high as 102 in the Bronx. Friday could deliver a similar scorcher. The temperature might drop a few degrees by Independence Day on Saturday.

“This is Texas hot, which we don’t usually see here, so it’s serious,” said Carolyn Olson, assistant commissioner for environmental surveillance and policy at the New York City Department of Health and Mental Hygiene.

On Monday, Mayor Zohran Mamdani ordered what City Hall called an “unprecedented, historic heat emergency plan.” Libraries, senior centers and other air-conditioned spaces were designated as cooling centers that will be open to residents seeking refuge from sweltering homes. City agencies also prepared to set up outdoor cooling stations, with misting fans in areas where outdoor workers, including street vendors and food delivery workers, gather regularly.

City Hall said that most large public pools would be open for an extra hour, until 8 p.m., and encouraged adults to borrow a spray cap from the nearest firehouse to turn the fire hydrant on their block into a sprinkler for children to play in.

Last week, Mr. Mamdani signed an executive order aimed at protecting people who are vulnerable to the heat, including about 93,000 people who work outside as street vendors, delivery workers and day laborers. Hundreds of thousands of others work as police officers and firefighters, maintenance and repair workers, and in many other jobs that put them under the sun for long periods.

The order instructs city agencies to examine how to strengthen workplace protections. The Department of Buildings, for instance, will review regulations to see if new safety requirements are needed to protect construction workers from heat exhaustion. The Health Department will study workers’ compensation claims to search for patterns linked to heat.

At a news conference announcing the mayor’s executive order last week, John Mosquera, who works at LaGuardia Airport, described loading bags onto a plane during a 10-hour shift on a scorching day last summer. He started seeing stars. “I lost consciousness and just laid in the belly of the plane from how hot it was,” Mr. Mosquera said.

Someone woke him up. “I had a short break and some water and was sent right back to work,” he said. “Nobody should collapse from heat on a job and then expect it to just keep going.”

The mayor’s executive order also requires city agencies to develop plans to prevent heat-related illnesses among municipal employees who work inside and outside. That provision echoes a Boston law that requires city work sites to provide workers with water and breaks in the shade and to maintain a “heat illness prevention plan.”

The initiatives are modest compared with some labor laws and government actions elsewhere. During a heat wave last year in southern Europe in which temperatures exceeded 115 degrees, some local governments from Greece to Spain ordered outdoor work to stop during the afternoons.

This week in New York, a high-pressure system called a heat dome, which can span up to 1,000 miles, is to blame for creating and containing the heat. Beyond New York City, temperatures in Washington and Philadelphia could climb past 100 degrees. Scorching days are expected across the Midwest, too.

In New York, city officials anticipate heat that could rival — or even surpass — last year’s heat wave, which peaked on June 24, 2025, when the city logged its hottest day in 15 years. Central Park reached 99 degrees, and Kennedy International Airport in Queens hit 102.

“We’re staring down what could be the second-hottest day in New York City history in over a decade,” Mr. Mamdani said.

The 2025 heat wave led to a sharp rise in heat stroke deaths.

On average, seven people in New York City die each summer because of heat. Last year, 21 such deaths were reported, with 19 of them attributed to the June heat wave.

It’s not just the days of record heat that worry public health officials. More days are in the high 80s and low 90s than in past decades. The number of days each summer with highs over 86 degrees have more than doubled during the last 50 years, rising to an average of 32 days from 14 days, according to the city Health Department.

There is a good chance of thunderstorms over the weekend, but the rain is not expected to bring much relief: Temperatures in the 90s are forecast until Monday.