For much of the nation, no relief from the heat is expected this weekend.
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On the first weekend of summer, a brutal heat wave has taken hold for a sixth consecutive day, continuing to scorch large swaths of the United States.
Temperatures across portions of the Midwest, Ohio Valley and Mid-Atlantic could break records again, while heat builds in the Southern Plains and the West.
In states like Ohio, Pennsylvania and Maryland, the humidity is making it feel hotter. By early Saturday afternoon, heat index values — a measure of how conditions feel with humidity taken into account — reached almost 100 in places like Philadelphia and Tampa, Fla. In Baltimore, it soared to over 100, and it is possible temperatures will keep climbing in some locations.
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In New York City, officials and utility providers are bracing the city for the lingering heat, which is expected to reach a heat index of 103 degrees between Saturday and Sunday. Already, the city has recorded temperatures it hasn’t seen in almost two years, with Central Park hitting 94 degrees on Friday.
Elevated temperatures raise the risk of heat-related power outages, but power grids in New York and across the country so far have largely held up.
Still, hazardous conditions remain. In Manhattan and cities including Indianapolis, Cincinnati and Pittsburgh, residents will face the highest level of health risk from the heat, according to a gauge by the National Weather Service and the Centers for Disease Control and Prevention. Their measurement, called HeatRisk, rates the danger in an area on a scale from zero to 4 based on factors that include the duration of the heat and how unusual it is for this time of year. Several other cities, including Fresno, Calif.; Wichita, Kan.; and Tampa, Fla.; were at Level 3, considered major a health risk.
C.D.C. data also showed that heat-related illnesses spiked this week in regions like the Northeast and the Midwest — areas that have been hit the hardest by the heat wave.
Though the heat wave will not fade over the weekend, conditions are expected to cool slightly on Monday. But even if they do, the country won’t be in the clear: Forecasters expect temperatures to still hover above average in the Mid-Atlantic States through the middle of next week.
— Kate Selig and Judson Jones
Heat-related illnesses spiked in some regions this week, C.D.C. data shows.
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Heat-related emergency room visits spiked this week in regions of the United States that had been hit the hardest by the heat wave, according to data from the Centers for Disease Control and Prevention.
Across swaths of New England, the Midwest and the Mid-Atlantic states, there were “extremely high” rates of heat-related illnesses this week, the C.D.C.’s heat and health tracker showed. The tracker only had data available through Thursday.
The data used emergency room visits associated with the heat to determine the rise in heat-related illnesses, showing which areas had visits that exceeded the 95th percentile of what is typical there. The numbers were based on a scale of per 100,000 visits.
In New England, the number of visits climbed from 57 per 100,000 on Monday, the first day of the heat wave, to 833 on Thursday — the highest rate in the country all week. The region is less acclimated to high temperatures this time of year, and places like Boston and Hartford, Conn., saw record temperatures of 98 and 97. Caribou, Maine, reached 96 degrees this week, tying the highest temperature ever recorded there.
Much of the Midwest also had higher-than-usual heat-related emergency room visits, reaching a peak of 628 visits on Wednesday. Chicago hit a record high of 97 degrees on Monday.
Areas around New York and New Jersey also saw a surge on Tuesday, Wednesday and Thursday, going up to 459 heat-related emergency room visits. New York City reached temperatures it hadn’t seen in almost two years, going up to 94 degrees in Central Park on Friday.
Deaths resulting from extreme heat have been on the rise in the country in the past few years. The C.D.C. recorded about 2,300 heat-related deaths in 2023, up from approximately 1,700 deaths in 2022 and about 1,600 in 2021.
Global warming has been making heat waves hotter, more frequent and longer lasting. And the longer a heat wave, the more health risks people face as each additional day of extreme heat further strains the body.
Temperatures in New England fell on Friday, but parts of the Midwest and Mid-Atlantic are expected to continue to bake through the weekend.
— Kate Selig
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The concrete jungle helps the sizzling heat feel even hotter.
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There’s a reason heat waves feel hotter in New York City: Concrete. And here in the city, we have a lot of it.
Our buildings, roads and sidewalks absorb the heat from the sun and then release it, a process known as the “urban heat island effect.”
A 2023 study on the phenomenon reported that New York City, followed by Newark, had the highest urban heat island, or U.H.I., index average of about 8.5 degrees. This means that if the temperature is 90 degrees, it feels more like 98.5. Other cities with high U.H.I. numbers include Miami, Seattle, New Orleans, Detroit and Chicago, all of which have averages of around 8 degrees.
When the National Weather Service releases heat index predictions, which factor humidity with temperature readings, it takes into account the urban heat island component, said Dominic Ramunni, a meteorologist at the weather service. “The value is baked into our computer model,” he said.
“Baked” is the operative word this weekend for those in New York and Newark, who are looking at a heat index of right around 100 through Sunday.
But there is a way for cities to mitigate against the heat: By incorporating more green spaces into our urban landscapes, said Amy Chester, the managing director of Rebuild by Design, a resiliency nonprofit.
“All the ways we make our cities beautiful also have the added benefit of cooling our air during heat waves, cleaning our air, absorbing rainwater to reduce flooding, raising the value of our homes and providing better health and mental health outcomes,” she said.
Trees provide shade, which lowers ambient temperatures, while green roofs, like the 6.75-acre one atop the Javits Center in Midtown, or the green terraces of Via Verde, an affordable housing development in the South Bronx, lower indoor temperatures, Ms. Chester said.
A glance at a heat map posted by the United States Geological Survey shows that temperatures in Central Park, for example, can be roughly five degrees cooler than more developed areas.
Case in point: Friday’s temperature in Central Park, a monitoring site for the National Weather Service, reached 94 degrees. At La Guardia Airport, another site with plenty of concrete and hardly any green, the high temperature was 97 degrees.
Temperatures in the city will hover in the 90s into the weekend, though potential rain could provide some relief. The Metropolitan Transportation Authority, which operates the city’s subway and buses, announced Friday that it would be on the lookout through the weekend for possible service disruptions linked to the heat.
— Hilary Howard
A short guide to understanding heat domes.
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Hearing a “heat dome” is in the forecast might spur feelings of dread. But how does a heat dome actually work?
Here’s what to know about the weather phenomenon.
What is a heat dome?
A heat dome is a high pressure system way up in the atmosphere that helps create and encase heat, kind of like a lid on a pot that holds in steam.
Heat domes “on the order of 1,000 miles across” can form under high pressure weather systems, said Hosmay Lopez, an oceanographer and expert on extreme heat and climate change with the National Oceanic and Atmospheric Administration. They become anchored in place, building up heat, sometimes for weeks at a time.
The term “heat wave” describes a rise in temperature in the weather pattern, and the term “heat dome” refers to a high pressure system that traps heat. The terms are often used interchangeably.
How do heat domes form?
When a high pressure system moves into an area, it pushes warm air toward the ground. With the sinking air acting like a cap, the warm air can’t easily escape, and it continues to heat up the more it is compressed.
“You can actually repeat this process on a small scale,” said Greg Carbin, forecast operations chief at the National Weather Service’s Weather Prediction Center. “When you’re inflating a flat tire, as the air goes in and the pressure builds, the molecules move faster, they are closer together, and they heat up.”
This high atmospheric pressure is linked to the configuration of the jet streams, bands of speedy winds that form high in the atmosphere in areas where cold air and hot air meet. The jet streams tend to be narrow, wavy corridors of air that move west to east and migrate north to south. Sometimes jet streams can expand, becoming slower, or even stagnant, and heavier.
Can heat domes happen anywhere?
Yes, they can, but areas that are farther from water, have flatter topography and are south of where jet streams migrate in the summer are more prone to oppressive heat domes. In the United States, that area is the Central Plains.
The heat domes that have covered the Pacific Northwest in recent years still baffle meteorologists, Mr. Carbin said, because the mountainous topography of the region is the opposite of what is usually conducive to heat domes.
Heat domes are associated with climate change. In the 1970s, there was one heat wave for every cold wave. As climate change accelerates, “that ratio is more than two to one, and for some places, it’s three to one,” Dr. Lopez said.
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Are heat domes dangerous?
Yes. Heat stress is the most common cause of weather-related deaths, according to the World Health Organization. Because heat domes are associated with stagnating air, they can also lead to reduced air quality, dryness and a greater chance of fire. “Those stains are very detrimental for human health, especially for the elderly and people with preconditions like cardiopulmonary illnesses,” Dr. Lopez said.
Read about staying safe in a heat wave here.
— Isabella Grullón Paz and Camille Baker
