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As a blistering heat wave continued to roast the eastern half of the United States, New York City, already thought of by its residents as an urban sauna on an average summer day, braced itself for the worst.
OZY Fest, a hybrid music-lecture-food festival that had been expected to draw tens of thousands to the Great Lawn of Central Park over the weekend, had been canceled, as had the New York City Triathlon. Both were called off at the request of city officials.
New Yorkers were also worried that the electricity grid would falter and plunge them into muggy darkness, as it had in parts of Midtown Manhattan last week. Others, undeterred by warnings of extreme temperatures, flocked to parks, pools and beaches.
The threat of the heat was serious enough that Mayor Bill de Blasio declared a state of emergency and cleared his presidential campaigning schedule so he could stay put all weekend. He had been criticized for being absent during the blackout last Saturday.
“This is a very, very difficult situation,” Mr. de Blasio said in a news conference on Friday. “Everyone’s got to take it seriously.”
The stifling humidity came amid an excessive heat warning for the greater New York City area that began Friday afternoon and was scheduled to last through Sunday evening.
The misery of people already struggling with the weather was compounded on Friday night, when several subway lines were suspended in both directions after an episode the Metropolitan Transportation Authority attributed to a “network communications” issue.
By Saturday, National Weather Service meteorologists said, temperatures in Manhattan could reach 97 degrees. They cautioned it could feel as high as 111.
“We have not seen temperatures like this in at least seven years,” Mr. de Blasio said on Friday.
Official said it was the hottest stretch of weather to hit the region in a summer that had been marked by relentless rain. The Weather Service defines a heat wave as three consecutive days of temperatures that hit 90 degrees.
The heat has been exceptional elsewhere in the nation. Dangerously hot weather stretched across much of the central and eastern United States earlier in the week, with ocean air trapped in a “heat dome” in the middle of the country. That air has reached the East Coast.
In New York City, high temperatures can feel particularly brutal thanks to the urban heat island effect, in which heat absorbed by asphalt and concrete makes cities significantly hotter than nearby suburbs — particularly at night, when the temperature gap can be as wide as 22 degrees.
To help residents and visitors, city officials said they had set up nearly 500 cooling centers for those without air-conditioning to cool off.
They also promised to put portable water fountains in places with heavy foot traffic and issued a Code Red alert to expand outreach efforts to homeless people, including the promise of transportation to cooling areas at shelters.
The parks department said it would keep sprinklers in parks running and extended the hours of city pools and beaches.
The prolonged heat and humidity were expected to test the city’s power system, as people stayed indoors and blasted their air-conditioners.
Anticipating the demand, the city, in statements, social media posts and news conferences, called on people, especially those in tall office buildings, to keep thermostats and air-conditioners set no lower than 78 degrees.
On Friday, ConEd’s president, Tim Cawley, said the utility was “very confident” that the power grid would withstand the heat.
But Mr. Cawley also said the system could be stressed on Saturday or Sunday by what ConEd expected to be an all-time-high energy demand on a weekend. To prepare, the company had scheduled 4,000 additional workers and extended employees’ shifts.
“It’s everybody in, everybody on,” Mr. Cawley said.
Reporting was contributed by John Leland, Patrick McGeehan, Jan Ransom, Andrea Salcedo and Nikita Stewart.
