Aggressive heat swept across the New York region as sweltering weather stifled the Northeast on Thursday, disrupting travel and prompting emergency measures as states took precautions against hazardous levels of heat and humidity before a holiday weekend.

The temperature in New York’s Central Park reached 100 degrees by 2 p.m., according to the National Weather Service, the first time it was that hot there since July 18, 2012. It also tied a record for July 2, as it was the first time the temperature in the park hit 100 on that date since 1966.

Some 163 million people — from Missouri to Maine and south to Mississippi — live in areas that were expected to experience dangerous heat Thursday, according to the weather service. Much of the weather that scorched the Midwest spilled over into the Northeast, sending “heat risk” forecasts in major cities — including New York, Washington, Philadelphia, Pittsburgh and Atlanta — into the most extreme risk category through Saturday.

Temperatures in those cities were hovering around 100 by noon Thursday, with several daily records at risk of falling.

Heat indexes — measures of how hot the air feels based on temperature and humidity — are surging across the eastern United States, meaning heat cramps or heat exhaustion are likely, and heat stroke is possible, with prolonged exposure or physical activity.

A weather station in Brooklyn, New York, recorded a heat index of 109, a threshold now fairly widespread across the East Coast.

In much of the Northeast, the temperature is not expected to dip much below 80 on Thursday and Friday night. By Saturday, many people will likely be facing the third or fourth consecutive day of stern warnings to avoid being outside in the hottest parts of the day.

Temperature-related conditions disrupted rail travel along parts of the Northeast Corridor. Local officials urged people to stay indoors, in air conditioning and to check on their neighbors.

Here’s What Else to Know:

— Why it’s hot: The meteorological phenomenon causing the extreme heat is a sprawling high pressure system, also known as a heat dome. Like a lid on a boiling pot, heat domes trap the air beneath them, pushing warm air toward the ground that, as it sinks, compresses and becomes much hotter.

— Global warming: While tying a single heat wave to climate change requires extensive analysis, scientists say that heat waves have grown longer, hotter and more frequent. The past 11 years have been the hottest on record.

— Cooling off: The extreme heat threatens the stability of electrical grids across the eastern United States. Cities and towns in many parts of the country have opened libraries, senior centers and other air-conditioned spaces. Experts urged residents to stay hydrated, plan their days around the heat and to know the warning signs of heat illness.

— When will it end?: For many, the heat wave will start to ebb Sunday, as the heat dome responsible starts to weaken. Many of the most extreme heat warnings will have passed, but dangerous heat is likely to remain across parts of the Washington metro area, Virginia and the Carolinas.

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This article originally appeared in The New York Times.

By Nazaneen Ghaffar, Erin McCann and Christine Hauser/Madeleine Hordinski
c. 2026 The New York Times Company