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A dangerous heatwave is set to intensify and spread across the eastern half of the United States this week, bringing extreme temperatures through to the Fourth of July holiday weekend.
Temperatures ranging from around 32°C to 40°C combined with high humidity will see local heat indices hit up to roughly 46°C, the National Weather Service has said.
The hot spell is likely to peak in the Midwest and Mississippi Valley from Tuesday through Thursday before moving into the Ohio Valley and East Coast on Thursday and into the weekend, according to the agency.
It warned that there will be “little to no overnight relief” from the heat, with temperatures only dropping into the 20°C range at night.
“This stretch of upcoming record-breaking heat from the Midwest to the East Coast will be particularly dangerous,” the NWS said on Tuesday. “This is due not only to the soaring daytime highs, but also the days-long duration of heat, and even morning lows that will be record warm – depriving areas of nighttime relief”.
The service added that such prolonged heatwaves are among the US’s most deadly weather events as “impacts are less visible and build over time”.
It comes after an early-summer heatwave gripped much of Europe in late June.
Parts of France, Spain and Germany topped 40°C last week, piling pressure on local health services amid a spike in heat-related emergencies.
Tedros Adhanom Ghebreyesus, the director-general of the World Health Organization, announced that more than 1,300 excess deaths recorded between 21 June and 28 June in Europe had been linked to high temperatures.
“Heat stress is often called the ‘silent killer’ – and European homes, workplaces and schools were not built for these temperatures,” he wrote in a post on social media.
Ghebreyesus said on Monday that the WHO had also partnered with FIFA to help protect players, staff and fans at the 2026 World Cup from the scorching temperatures facing the US.
The agency is “supporting the development of action plans, raising awareness, establishing early warning systems, improving access to safe drinking water, and implementing cooling strategies and smart planning,” he said.