US braces for prolonged heatwave as fourth of July travel peaks

More than 120 million people across the United States are facing dangerous heat conditions as a powerful and long-lasting heatwave tightens its grip on large parts of the country ahead of the Fourth of July holiday weekend.

Forecasters say the extreme weather will bring a combination of intense daytime temperatures, high humidity and very warm nights, increasing the risk of heat-related illnesses across a wide stretch of the country.

According to the National Weather Service (NWS), millions of Americans were under extreme heat warnings by Tuesday as the heatwave expanded from central parts of the country toward the East Coast.

The weather system, driven by a heat dome, is expected to strengthen through the week. The hottest conditions are forecast in the Midwest and Mississippi Valley by Thursday before spreading into the Ohio Valley and the eastern United States through the holiday weekend.

Temperatures are expected to range between 35C and 40.6C, while high humidity will make conditions feel even hotter. Forecasters warned that heat index values could climb to between 38C and 46C in some areas.

The NWS said several daily temperature records could fall on Thursday and Friday, with the possibility of monthly and even all-time records being broken in some locations.

Authorities have urged residents in affected regions to reduce time spent outdoors, drink plenty of water and seek access to air-conditioned spaces or designated cooling centres.

In New York City, Mayor Zohran Mamdani activated the city's heat emergency response plan, with hundreds of cooling centres scheduled to open on Wednesday to help residents cope with the rising temperatures.

Detroit, Michigan, where temperatures could reach 38C, also opened more than a dozen air-conditioned recreation centres to provide relief for residents.

The heatwave is also raising concerns around sporting events linked to the ongoing World Cup. Forecast conditions could push heat index levels beyond the threshold that global players' union Fifpro considers unsafe for play.

Texas is expected to experience some of the most intense heat, particularly affecting supporters travelling to and from air-conditioned stadiums in Houston and Arlington.

Similar concerns have been raised ahead of the England versus DR Congo match scheduled for Wednesday in Atlanta, Georgia.

In Philadelphia, organisers of the Fifa World Cup Fan Festival announced plans to move parts of the event into cooled tents on Thursday and Friday as temperatures rise.

The extreme heat is not limited to the United States. Canada is also dealing with a major heatwave, with temperatures in parts of Ontario expected to reach 37C this week.

The hot conditions are forecast to continue until at least Thursday, with Toronto expected to experience temperatures of around 35C on the day it hosts a World Cup match.

Canadian authorities have issued orange heat warnings across Ontario, the second-highest level in the country's three-tier warning system.

Other areas in central and eastern Ontario, as well as Montreal, are also expected to face elevated temperatures. Yellow heat warnings, the lowest alert level, have been issued in several regions as officials monitor the situation.

The North American heatwave comes only days after several European countries experienced an unusually early and intense spell of extreme temperatures, with records broken in multiple locations across the continent.