Carlos Reyes sought shade under a tree in the Bronx on a day that felt like it was over 38 degrees Celsius because of the heat and humidity.
"It's not like when you were younger, you were playing around," said the 56-year-old who runs a daycare center. "Now it's like you got the humidity. It makes you kind of not breathe the same way. So when you walk, you get a little more tired, a little more exhausted."
Reyes was one of nearly 200 million people in the United States, or 60% of the U.S. population, who had been under a heat advisory or flood warning or watch since Thursday, according to the National Weather Service.
Dangerous heat engulfed much of the eastern half of the United States on Friday as extreme temperatures spread from the Midwest into the Northeast and mid-Atlantic where some residents saw their hottest temperatures of the year.
Although much of the country does not cool much on normal summer nights, night temperatures are forecast to stay hotter than usual, prompting excessive heat warnings from the Plains to the East Coast.
From Thursday to Friday, the number of people under a heat advisory rose from 180 million to 184 million and the number of people under a flood warning or watch dropped from 17 to 10 million.
Moisture moved into the Southwest, cooling somewhat the southernmost counties of California and parts of southern Arizona, but excessive heat warnings remain for much of the region.
On top of the heat, severe thunderstorms were forecast for multiple regions of the country. There were forecasts with flash flood warnings for Great Lakes and Ohio Valley, west to the middle Missouri Valley through Saturday morning.
Tornado watches were posted in Wisconsin and New Hampshire, in addition to the heat advisories and potential for severe storms.
The prediction for continued excessive heat came as the World Meteorological Organization and the European Union's Copernicus Climate Change Service declared July 2023 the hottest month on record.
Scientists have long warned that climate change, driven by the burning of fossil fuels, by deforestation and by certain agricultural practices, will lead to more and prolonged bouts of extreme weather.
On Thursday, heat and humidity in major cities along the East Coast, including Washington, Philadelphia and New York City, made it feel above 37.8 degrees Celsius. Forecasters expected several records might break Friday with temperatures 5.5 to 8 degrees Celsius above average.
The "dangerous" heat wave, as the National Weather Service called it, may begin to subside Saturday as thunderstorms and a cold front from Canada progress through the region. It seems the hottest temperatures happened on Friday.
The Salvation Army in the Bronx was one of hundreds of cooling centers open in New York City to give people a respite from the scorching heat.
"It's very hot every year. This year, it started last week, becoming very hot," said Robert Ciriaco, a corps officer with the Salvation Army. "[It's] very dangerous for people. Some people die. So that's why we open - to offer people [a place] to come to be comfortable."
Philadelphia declared a heat health emergency as temperatures soared past 32 degrees, and city authorities opened cooling centers.
But some residents took the heat in stride. Alexander Roman, who took his children to play in the fountain at the city's iconic Love Park, said he was not worried about heatstroke as long as his family could cool down. "A lot of water with ice and it will be OK," he said.
In the Southwest and southern Plains, oppressive temperatures have been a blanket for weeks. One meteorologist based in New Mexico called the prolonged period of temperatures above 37.8 Celsius unprecedented.
Because of the extreme heat, some of the nation's large power grids and utilities were under stress, which could affect Americans' ability to cool off.
In New York City, utility Con Edison sent out a text blast asking residents to be frugal with air conditioning to conserve electricity. Overtaxing an electrical grid can mean blackouts, which are not just an inconvenience, but can lead to equipment failures and major pollution as equipment restarts.
The country's largest power grid, PJM Interconnection, declared a level one energy emergency alert for its 13-state grid on Wednesday, meaning the company had concerns about its ability to provide enough electricity.
PJM wasn't the only electrical grid to issue such an alert. The Midcontinent Independent System Operator, which mostly covers states in the Midwest and northern Plains, issued a similar one Thursday.
The dangerous heat was expected to peak in the Northeast, mid-Atlantic and Midwest on Friday and Saturday before a cold front brings some relief Sunday and into next week.
