The scorching heat wave gripping the country ahead of the summer solstice could intensify in the coming days, breaking records and affecting more than 135 million people, meteorologists warned on Wednesday.
According to AccuWeather, temperatures will reach 90 degrees Fahrenheit from the Ohio Valley through the Mid-Atlantic and into New England, with some locations potentially reaching over 100 degrees Fahrenheit.
Some parts of the U.S. not used to extreme heat were already feeling the effects Wednesday, including Caribou, Maine, where records date back to 1939. “The heat index in Caribou is currently at 103 degrees,” the weather service said in a social media post. “This is an unofficial all-time high.” Some parts of the state could see the heat index rise even further on Thursday, reaching 105 degrees, according to the National Weather Service.
Daytime temperatures around Pittsburgh are expected to reach 110 degrees Fahrenheit through Saturday. Heat index values in northwest Ohio and northern Indiana are expected to reach 102 degrees Fahrenheit through Friday. Temperatures in Washington, D.C., could rise to 101 degrees Fahrenheit on Sunday.

Forecasters said overnight temperatures will drop into the 70s Fahrenheit, but that won’t provide much relief. The National Weather Service warned that high humidity will significantly increase the chances of heatstroke, especially for people who work outdoors.
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“Daytime temperature records will be broken across the Ohio Valley and Northeast on Wednesday and Thursday as high pressure continues to develop in the east. Highs will be in the 90s and 100s Fahrenheit, bringing with them the risk of heatstroke across the region,” AccuWeather Meteorologist Alex Duffus said.
No relief from the heat is expected until late next week as a cold front cools parts of the Midwest and Northeast, according to AccuWeather.
Unprecedented heat in Maine
Angela LaFlash is a meteorologist at the NWS observation station in Caribou, Maine, where temperatures have been rising since Tuesday to unprecedented levels.
“Oh my gosh, the heat here is unbelievable,” LaFlash said. “Yesterday we had the first heat warning in the history of our office, so hot it was.”
According to the Maine Weather Service, a heat warning is issued when the heat index exceeds 105 degrees for more than two hours.
LaFlash said temperatures are typically in the mid-70s in the area, but this heat is well above average.
Steven Barron, a meteorologist with the NWS station in Gray, Maine, who also issued the extreme heat warning, said heat like this doesn’t usually hit southern Maine until mid-summer in August.
“It’s considered dangerously hot,” he said. “If you have to be outside, take breaks and remember to stay hydrated.”
LaFlash said a cold front moving down into northern Canada will begin to cool the region by Thursday evening and could bring rain.
The heat isn’t just in the Northeast
The heatwaves aren’t just being felt in the Northeast and Midwest. The National Weather Service has issued extreme heat warnings for much of southern Arizona. Temperatures in Phoenix and Tucson have topped 102 degrees Fahrenheit and are expected to reach as high as 113 degrees on Thursday as dry, hot winds continue to dominate the region.
Chris Rasmussen, a meteorologist with the NWS office in Tucson, said this was the fourth extreme heat warning the agency has issued so far this year, but conditions remain dangerous for local residents.
“It’s so routine that it’s easy to forget what to do,” the Tucson native said. He added that outdoor activities should happen in the morning, rather than waiting until the afternoon. “The heat is pretty intense, so people should be aware and take precautions.”
Rasmussen said the heat could bring on monsoonal weather by the evening, with Tropical Storm Alberto bringing even more moisture to the region.
Tips to prevent heat stroke
The Centers for Disease Control and Prevention, the Weather Service and other agencies advise people not to go outside during the hottest parts of the day when heat advisories are in effect, and for those who don’t have that option, experts urge them to work in the shade, take frequent breaks and stay well hydrated.
During hot weather, temperatures inside a car can reach lethal levels within minutes, and the Met Office warns people should never leave children or pets in a car, especially during a heatwave.
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Those most at risk, according to the CDC, are young children, older adults, people who work outdoors, people with chronic or mental illnesses, and people who take certain medications that make it hard to regulate their body temperature. Also at risk are people who don’t have access to reliable air conditioning, as well as people who live in what are known as urban heat islands, areas with little green space and lots of sidewalks and buildings that cause high temperatures.
Experts previously told USA Today that it’s best to check in on anyone who may be sensitive to the heat.
To contribute: Gabe Haouari, USA Today