Volkswacht Bodensee - Oppressive heat broils US during World Cup, July Fourth

"Heat dome" conditions -- in which high-pressure systems trap warm air like the lid on a pot -- persisted over the Midwest and South and were moving east, with some 46 million people under heat alerts.

"We are entering what could be the most extreme heat wave this city has seen in over a decade," New York Mayor Zohran Mamdani said in a video, adding he wanted people to stay safe while watching the World Cup, celebrating the Fourth of July -- "or, renting out MSG to get married, hypothetically."

Pop superstar Taylor Swift is rumored to have rented Manhattan's famed Madison Square Garden venue for her weekend wedding to American football star Travis Kelce.

New York has designated hundreds of public buildings as cooling centers, extended public swimming pool hours, dispatched volunteers to check on vulnerable residents, and opened "pop up" cooling stations with misting fans and wet towels.

More frequent, longer-lasting and more intense heat waves are one of the clearest signs of climate change, with Europe also recently hard hit.

Global average surface temperatures have risen roughly 2.5F above pre-industrial averages as a result of human-caused climate change, mainly driven by the burning of fossil fuels.

- Records set to fall -

From Thursday, the US capital Washington is forecast to have three consecutive days above 100F (38 C) -- the highest on Friday, when the mercury could touch 104F.

If the forecast bears out, the city's daily heat records would be broken each day, while Washington's all-time high temperature of 106F could also be in danger.

The heat comes as the nation prepares to celebrate on Saturday the 250th anniversary of its independence from Britain, with fireworks set to light up the skies over major cities, including New York and Washington.

Fireworks trigger spikes in harmful fine particulate matter that cause respiratory issues, with the combined effects of heat and smoke amplifying health impacts.

Jaden Martin, a 22-year-old who works in marketing and hails from the southwestern state of Arizona, told AFP he was visiting the capital to accompany his girlfriend who was attending a mathematics conference.

"We're good with the heat, but the humidity is a different beast," he said as he wheeled his rental bicycle along a section of the National Mall crowded with tourists.

- Frequent AC breaks -

Teachers Cecile Hansen and Peter Helmkamp, who had traveled from Miami, Florida to attend the "Great American State Fair" recommended fans, sunblock, visors, and dipping into air conditioned cafes every 20 minutes.

"Drink lots of water and try to freeze a bottle of water before you come out," added Hansen, 50, who was carrying a handheld electric fan.

Meanwhile, football's World Cup is taking place under punishing conditions.

A high of 102F is forecast for Saturday's clash between Paraguay and France in Philadelphia, where the game will be played in an open-air stadium, unlike some World Cup venues which are air-conditioned.

This edition of the World Cup requires players to take a three-minute "hydration break" every half.

K.Hofmann--VB