A severe and prolonged heatwave is sweeping across the United States, placing tens of millions of people under extreme heat warnings and disrupting major public events, including the country’s 250th Independence Day celebrations and World Cup football matches. The National Weather Service has forecast heat indices—what the temperature feels like with humidity—reaching 43°C to 46°C in cities from the Midwest to the East Coast. In New York, the heat index is expected to hit 43°C, a level recorded only three times in 80 years, according to local officials. Mayor Zohran Mamdani warned that the heat was “not a normal summer heatwave” but “dangerous heat that can be fatal.” Washington D.C. is forecast to see 38°C on Saturday, with humidity making it feel like 43°C. Authorities in multiple cities have activated emergency plans, opened cooling centres, and urged residents to limit outdoor activity. Amtrak cancelled over a dozen trains in the Northeast on Thursday due to heat-related infrastructure concerns.

The heatwave coincides with the Fourth of July weekend, when millions are expected to gather for fireworks and speeches. In Washington, the official celebrations on the National Mall will open gates at 1 p.m., with President Donald Trump scheduled to speak at 9:45 p.m. and fireworks not due to begin until 10:30 p.m. or later. The White House has said standard contingency plans are in place, including water and misting stations, but has not detailed any schedule changes. President Trump, speaking in North Dakota, said he would deliver “a really long speech, just to show that I can do anything,” despite the forecast. Meanwhile, the World Cup, co-hosted by the US, Mexico and Canada, faces similar strains. A United Nations climate secretariat report found that 26 of the tournament’s 104 matches pose a real health risk to players and fans, with at least five potentially exceeding the threshold for postponement. The players’ union has called for delays after group-stage matches saw temperatures above 28°C. Only three of the tournament’s stadiums have retractable roofs and full air conditioning; the rest are open-air venues.

Extreme heat is the deadliest weather-related hazard in the United States, with at least 13,000 deaths recorded since 2018, according to the Centers for Disease Control and Prevention. The current heat dome is also straining power grids: in Chicago, utility ComEd asked customers to reduce consumption immediately, though no outages had been reported as of Thursday. Meteorologists warned that overnight temperatures would offer little relief, compounding the danger. As of Thursday, no fatalities had been directly attributed to the ongoing heatwave, but authorities across more than two dozen states maintained excessive heat warnings, with the most severe conditions forecast for the East Coast on Friday and Saturday. Event organisers and emergency services continue to monitor the situation.