NEW YORK (AP) — The temperature in New York City reached 100 degrees Tuesday as the eastern U.S. sweltered under an extreme heat wave.

Kennedy International Airport recorded 100 degrees Fahrenheit (38 Celsius) at midday, according to the National Weather Service.

Large swaths of the country were broiling under a heat dome, worsened by a humid atmosphere that’s circling the East.

Following nearly 40 U.S. cities setting new record high temperatures on Monday, the weather service predicts numerous additional records on Tuesday as the heat dome is expected to reach its zenith.

But just as dangerous as triple digit heat is the lack of cooling at night, driven by that humidity.

Amtrak reported delays Tuesday due to speed restrictions caused by the heat on routes that went through Washington, Philadelphia and New York.

In different regions, the intense heat has posed serious threats. On late Monday afternoon, two 16-year-old hikers were rescued from a mountain in Jaffrey, New Hampshire, after being overwhelmed by the high temperatures, according to the New Hampshire Fish and Game Department. Both were semi-conscious and transported to a hospital for treatment.

This heat wave poses a significant risk as it affects cities like Boston, New York, and Philadelphia at the onset of summer, a time when residents have not yet acclimatized to such oppressive heat, according to several meteorologists. The high-pressure system positioned over the eastern U.S. is holding in hot air from the Southwest, which has already caused discomfort in the Midwest.