Wandering an aisle at Spirit Halloween in Manhattan’s Chelsea neighborhood this week, Clay Smith was deciding whether to pivot his costume from a warm, one-piece banana suit to a lighter outfit, like perhaps that of a pool boy.

Krystal Colon, who was also Halloween shopping, said she was skipping the annual parade in Greenwich Village and would instead celebrate her favorite holiday away from the city.

“With the heat and the subway and the costumes,” she said, “it’s going to be too much to handle.”

Temperatures on Halloween are expected to reach the mid-to-upper 70s in New York City, far from the crisp fall days New Yorkers are used to this time of year.

“I don’t think, living here all my life, it’s been 80 degrees on Halloween,” Mr. Smith, 26, who grew up in Brooklyn, said. While it’s not forecast to hit 80 degrees, it may get close.

“I don’t think I like it,” he added.

Cities across the Northeast may experience temperatures in the high 70s and lower 80s on Thursday, according to the National Weather Service, which said on Tuesday that it could be one of the warmest Halloweens on record for the region.

It has been a relatively warm month for the city, ranking in the 25 warmest Octobers in New York City in 155 years of record-keeping, and Halloween is likely to be the warmest day this week. The temperature on Thursday is expected to fall short of the record high temperatures of 81 degrees set at Central Park in 1946.