Emergency declared as US states brace for 40C-plus heatwave

More than 200 million Americans were today warned about a “widespread and dangerous” heatwave this weekend with swathes of the country expected be as hot as California’s Death Valley.

The National Weather Service was predicting record 40C-plus temperatures and humidity in several states, with New York, Michigan and Kansas set to see the hottest conditions.

Washington DC was forecast to bake in 38C (100F), but it will feel closer to 43C (110F) — prompting mayor Muriel Bowser to declare a heat emergency.

New York mayor Bill de Blasio last night warned residents to stay hydrated and to avoid leaving children in cars. In a video on social media, he said: “Friday is going to be bad. Saturday is going to be really, really bad. Take it seriously.” About 500 cooling centres have been set up in the city.

Extreme heat and humidity was set to grip the urban corridor from Washington DC to Philadelphia and New York, starting this evening with overnight temperatures no cooler than 27C (80F).

Philadelphia in Pennsylvania has never experienced weather hotter than 36C (97F), but is expected to set a new record with 38C (100F).

Other east coast cities that could see records fall are Atlantic City in New Jersey and Richmond in Virginia, which could both hit triple-figure Fahrenheit temperatures for the first time.

Meteorologist Jim Hayes, of the NWS, 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.”

A cooler front was expected to break through late on Sunday, bringing the mercury down to more typical July temperatures of 30-32C (85-90F) on Monday and Tuesday, Mr Hayes said.

In Chicago, the heatwave prompted housing officials to conduct health checks. Ambulances in Oklahoma City and Tulsa have responded to more than 40 heat-related calls since Tuesday.

Jennifer Francis, of Woods Hole Research Center in Massachusetts, which studies climate change, said heatwaves were becoming more common and “normal itself is getting warmer”.