The eastern half of the United States is in the grip of a prolonged and dangerous heatwave, with air temperatures exceeding 38°C (100°F) and humidity driving the heat index above 46°C (115°F) in major population centres. The extreme weather coincides with America’s 250th independence anniversary and multiple World Cup fixtures, compelling authorities from the Midwest to the Atlantic coast to cancel or curtail public events.

According to the National Weather Service, some 238 million people — roughly 70 per cent of the U.S. population — are under excessive heat warnings or advisories. The heat dome, a persistent high-pressure system trapping hot air, is expected to break hundreds of daily temperature records. In Washington, D.C., forecasts indicate the mercury could reach 42°C (107°F), surpassing the 2019 record of 37.8°C; New York City is likely to hit 38°C for the first time in more than a decade. Overnight lows offer little respite, remaining above 27°C in many urban areas.

Local officials have opened cooling centres, deployed mobile health units and urged residents to stay indoors. New York City Mayor Zohran Mamdani described the conditions as “extremely dangerous,” while Philadelphia shortened its Independence Day parade and Amtrak cancelled some train services. President Trump, however, insisted he would deliver “a really long speech” outdoors at the Salute to America 250 celebration on the National Mall, where organisers plan a record 860,000 pyrotechnic effects. Environmental groups warned that the fireworks, combined with stagnant air, risk producing hazardous concentrations of fine particulate matter.

The heatwave strains the football World Cup, co-hosted by the United States, Canada and Mexico. Open-air stadiums in Philadelphia and Toronto face kick-off temperatures near 35°C; player unions have called for match delays. The United Nations climate body identified 26 tournament fixtures as posing significant health risks, with five matches potentially exceeding postponement thresholds. Power grids remain under extreme stress, with utilities in Chicago and New York urging consumers to reduce electricity use to avert blackouts.

The National Weather Service expects the heatwave to begin easing from Sunday, but heat warnings remain in effect for several more days. Officials continue to monitor conditions for the millions gathered at holiday and sporting events across the region.