Temperature records could fall as a "widespread and dangerous" heatwave descends on central and eastern parts of America.
The National Weather Service is predicting high temperatures and humidity across several states, including Michigan and Kansas, while Washington DC will feel almost as hot as Death Valley in California.
The capital will bake in a forecast high of 38C (100F), but it will feel closer to 43C (110F) – prompting mayor Muriel Bowser to declare a heat emergency.
Her Philadelphia and New York counterparts have followed suit, with hundreds of cooling centres to be set up in the latter to help people cope.
New York mayor Bill de Blasio said: "Extreme heat is dangerous, period. I urge all New Yorkers to exercise caution this weekend as temperatures near 100F (38C). We are deploying all resources at our disposal to ensure New Yorkers remain safe and cool during extreme heat."
The heatwave is expected to peak on Friday and Saturday, but has already had an impact in some parts.
In Shawnee, Oklahoma, a road buckled under the heat – and in Chicago cooling centres like those planned for New York have already been opened.
More from US
Philadelphia in Pennsylvania is one of the most likely to set a new record high.
The city has never experienced the mercury going higher than 36C (97F), but it has been tipped to hit 38C (100F).
Other east coast cities that could see records fall are Atlantic City in New Jersey and Richmond in Virginia, which could both record triple-figure temperatures for the first time.
Meteorologist Jim Hayes, of the National Weather Service, said: "It will be about as sweltering as it gets in some places in the eastern and central US.
"We're really more concerned about the combination of high temperatures and high humidity causing people stress, because it's more difficult to cool yourself down when there's moisture in the air."