It's all over the national news: Sweltering heat continues in the east, with temperatures in the 90s.
"When we pump in more humidity, heat index values will approach 110 degrees in Philadelphia," Kate Bilow of Philadelphia's KYW-TV told CBS' "This Morning" program.
With air conditioning, many people say 110 degrees is no big deal in Phoenix.
"It seems that people in the desert have acclimated and know how to avoid the hottest parts of the day," said Dr. Frank Cuntursi, who works in the emergency room at Banner Thunderbird Medical Center.
But Bilow says 110 is a problem in Philly.
"Here in Philadelphia, we have a unique challenge," Bilow said. "We have a lot of historic brick row homes that retain a lot of heat. They don't cool down overnight, and many folks don't have air conditioning. It can be a very dangerous situation."
Even though Arizonans may be used to the heat, Cuntursi said they need to use common sense and stay cool.
"If you have to go to the mall to cool off because you can't afford to run your air conditioning during the heat of the day, do it," he said. "Find shade, or get to a friend's house that might be cooler than yours."