WASHINGTON, United States (AFP) — Blistering temperatures and humidity gripped swaths of the United States on Wednesday, with the worst yet to come for the densely populated East Coast as the nation co-hosts the World Cup and prepares to celebrate its 250th birthday.

“Heat dome” conditions — in which high-pressure systems trap warm air over a region like the lid on a pot — persisted over the Midwest and South and were moving to the east, with some 46 million people currently 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 that he wanted to make sure people stayed safe while watching the World Cup, celebrating July Fourth “or, renting out MSG to get married, hypothetically.”

Pop superstar Taylor Swift is widely believed to have rented Manhattan’s iconic 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 2.3F above pre-industrial averages as a result of human-caused climate change, mainly driven by the burning of fossil fuels.

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.

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 other World Cup venues which are air-conditioned.

This edition of the World Cup requires players to take a three-minute “hydration break” every half — with Saturday’s searing temperatures, the breaks will be much-needed to stave off heat illness.