Updated at 6:32 p.m. July 20.
The National Weather Service warned Saturday that a "dangerous heat wave" paired with high humidity in the United States over the weekend could quickly cause heat stress or heatstroke if precautions were not taken.
Events were canceled throughout the nation, from festivals and concerts to sporting events.
The NWS said temperatures would remain warm at night, in the upper 70s to low 80s Fahrenheit, with more heat on the way Sunday for the East Coast. The agency also advised people to check in on relatives and friends, especially the elderly.
During a span of three days in July 1995, more than 700 people died in Chicago, when temperatures rose above 97 F (36 C). Many of those who died were poor or elderly with no access to air conditioning. Many also lived alone.
Despite the warnings, one runner in the nation's capital planned to head out for a run early Saturday. "It's brutal,'' Jeffrey Glickman, 37, said, adding, "You just have to power through it the best you can."
Temperatures have been rising in cities from the Midwest to the East Coast because of a high-pressure system that has trapped the warm air. City officials are allowing public pools to stay open longer and municipalities are issuing advisories to inform the public about how best to deal with the heat.
Temperatures in New York City reached 93 F (34 C) Saturday, but with the humidity, it felt like 106 (41).
Saturday in Washington, D.C., temperatures reached 97 F (36 C). Philadelphia hit 98 (37); with the humidity factored in, the heat index was 109 (43).
Storms throughout the Midwest knocked out power to hundreds of thousands of people in parts of Michigan and Wisconsin. Strong wind and rain were expected to persist Saturday night and into Sunday in the Midwest and Central Plains, which would bring cooler temperatures by Sunday.
The East won't be so lucky until Monday, the weather service warned. The heat will be the worst from the Carolinas to Maine.
The World Meteorological Organization saif June 2019 was the planet’s warmest month ever. In addition, both land and sea temperatures set record highs in June.
June was also Europe’s hottest June on record, according to the WMO. Greenland, Alaska and parts of South America, Africa and Asia had temperatures substantially above normal in June, according to the WMO. The organization said India and Pakistan experienced a severe heat wave in the early part of June, before the onset of the monsoon season.