Things are about to heat up in much of the U.S. with dangerously hot temperatures in the Midwest and Northeast next week, prompting health officials to urge people to make plans now to stay safe. A heat wave was already driving up temperatures in many southern states over the weekend, with heat watches, warnings, or advisories in place for almost 61 million people nationwide as of Sunday morning.

The heat wave follows an earlier-than-usual one in the Southwest last week, which saw triple-digit temperatures in places like Phoenix, where there were 645 heat-related deaths last year. Temperatures had reached 111 degrees Fahrenheit in the Arizona city by 5 p.m. on Saturday, and they ultimately climbed even further to a high of 112 degrees before the end of the day. The National Weather Service in Phoenix said that the reading was seven degrees above the average temperature recorded on June 15 in previous years — which is 105 degrees — but it remained below the record-high of 115 degrees recorded in 1896 and 1974.

The world has seen record-high temperatures this year, with more than three-quarters of the global population experiencing at least one month of extreme heat. 

Last year the U.S. had the most heat waves — abnormally hot weather lasting more than two days — since 1936. In the South and Southwest, last year was the worst on record, according to the National Oceanic and Atmospheric Administration. 

The next heat wave will ramp up Sunday in the center of the country before spreading eastward, the National Weather Service said, with some areas likely to see extreme heat reaching daily records. The heat wave could last all week and into the weekend in many places. Parts of the country will also see a heat dome, where hot air is trapped by the atmosphere. 

What areas will see extreme heat? 

There will be areas of extreme heat — when there's little or no overnight relief — from Texas to Maine, according to a National Weather Service heat risk map. Extreme heat will quickly spread eastward from the Plains states on Sunday, seeping into the Great Lakes and Upper Ohio Valley regions on Monday and reaching the Northeast on Tuesday, according to the Weather Prediction Center's latest outlook.

Temperatures are expected to peak in the mid- to high-90s in the Mid-Atlantic region and New England, which, National Weather Service meteorologist William Churchill told the Associated Press, is "nothing to sneeze at even in the middle of the summer, let alone this early in the summer." Increased humidity will make things feel hotter in many places, Churchill said, while the weather prediction center noted that those peak temperatures are likely as far north as Vermont and New Hampshire. 

Forecasters predicted the heat could set daily and potentially monthly temperature records in the Ohio Valley and Northeast, with the dew point making some areas feel as hot as 105 degrees, according to the weather service. There is even a low chance that temperatures in northern Maine will reach 100 degrees, David Roth, a forecaster with the Weather Prediction Center, told AP.

"The town of Caribou in northern Maine usually counts how many 80-degree days they have in a year. The fact that they have any chance of reaching 100 is very unusual," Roth said.

In Pittsburgh, an excessive heat warning was set to take effect Monday and last through the week as the city braced for a surge of hot weather. The temperature Monday could break or tie the city's daily record of 95 degrees, CBS Pittsburgh reported, adding that it will likely feel like triple-digit weather. Pittsburgh has not seen a heat wave as severe as the current one since 1988, according to the station.

It'll be the Detroit metro area's worst heat wave in 20 years or more, with temperatures forecasted in the mid-90s and heat indices around 100 F starting Monday and potentially lasting into the weekend, National Weather Service meteorologist Steven Freitag said. There's a chance the area could see its first 100-degree day since July 2012.

Although nighttime temperatures will dip into the 70s, providing some relief, the duration of the heat can have a cumulative and potentially dangerous effect on the body, Freitag said.

What are the dangers of extreme heat? 

Heat-related illness can be deadly if not recognized and treated early, and often starts with muscle cramps or spasms, experts say. Heat exhaustion and heat stroke could follow. In the United States, an estimated 1,220 people are killed each year by extreme heat, according to the Centers for Disease Control and Prevention, which notes in heat safety guidelines that all heat-related illnesses and deaths are preventable.

Symptoms of heat exhaustion may include heavy sweating and fatigue; a weak pulse; skin that's cool, pale or clammy; and headache, dizziness, nausea and fainting. The person should be moved to an air-conditioned space and offered sips of water. Loosen their clothing and apply cool, wet cloths or put them in a cool bath. Seek medical help if they vomit.

A person suffering heat stroke may experience headache, confusion, nausea, dizziness and a body temperature above 103 degrees. They also may have hot, red dry or damp skin; rapid pulse and faint or lose consciousness. The CDC advises people to call 911 immediately and, while waiting for help, use cool cloths or a cool bath and move them to an air-conditioned space, but do not give them anything to drink.

A National Institutes of Health-backed study published in 2023 projected an increase in heat-related deaths from 2036 to 2065 because of rising temperatures. 

"Climate change and its many manifestations will play an increasingly important role on the health of communities around the world in the coming decades," lead study author Dr. Sameed Khatana, assistant professor of medicine at the University of Pennsylvania and a staff cardiologist at the Philadelphia Veterans Affairs Medical Center, said in a news release. "Climate change is also a health equity issue as it will impact certain individuals and populations to a disproportionate degree and may exacerbate preexisting health disparities in the U.S."

Young children and infants, pregnant women, the elderly and people with chronic medical conditions are especially vulnerable, as are those who can't get around well or who live alone. The NIH-backed study also said Black Americans may be more at risk for heat-related deaths or illnesses. 

How can you stay safe from extreme heat? 

Stay indoors in an air-conditioned space and limit outdoor activities during periods of extreme heat, experts said. If you don't have air conditioning, find out if your community will open cooling centers. But even those with air conditioning should plan ahead in the event of a power outage, said Freitag, from the National Weather Service. Limit outdoor activities to the morning or, better yet, don't go outside, he said.

Other tips from the Centers for Disease Control and Prevention:

1. Drink plenty of water and take a cool shower or bath.

2. Wear lightweight, loose-fitting clothing, and use your stove and oven less.

3. Check on friends and relatives, especially those without air conditioning.

Communities also can prepare by opening cooling centers in places like schools and libraries. Some also send text messages to residents or have hotlines that people can call for help.

In Franklin County, Ohio, the office on aging is distributing fans to residents 60 and older, spokeswoman Kristin Howard said.

And some businesses whose employees work outside say they will start earlier to avoid the worst heat.

"When you get this sort of heat, any outdoor activities has to be a short duration (preferably) ... in the early morning hours," said Freitag. "But otherwise, there really shouldn't be any outdoor activity with physical exertion during the peak of the day."

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