Washington’s July 4 fireworks display will be the largest in the city’s history and will start significantly later than usual, organizers said Tuesday, as the nation marks its 250th anniversary with an event featuring military flyovers, enhanced security and extreme heat.

The pyrotechnics on the National Mall will not begin until 10:30 p.m. and may start as late as 11 p.m., according to a representative for Freedom 250, the public-private partnership established by the Trump administration for the semiquincentennial. Fireworks displays on the Mall typically start around 9:30 p.m.

The show is expected to last about 40 minutes — roughly twice the usual 17 to 25 minutes — and will include more than 850,000 fireworks launched from 10 locations around the area, according to The Washington Post, which cited Stephen Vitale, CEO of Pyrotecnico, the company producing the show. A typical July 4 display over the National Mall uses about 20,000 fireworks, Vitale said.

President Donald Trump has said he will speak at the event at 9 p.m., calling it “a rally.”

Jeff Carroll, interim chief of the D.C. Metropolitan Police Department, said the holiday will have “the largest display of fireworks our city has ever seen,” CBS News reported. The event will also feature military flyovers earlier in the day.

Security measures will be extensive. Tara McLeese, special agent in charge of the Secret Service’s Washington field office, said attendees watching from the Washington Monument grounds should expect “TSA-style” security, CBS News reported. New rules ban coolers, chairs, bags and more than one bottle of water.

Officials at Ronald Reagan Washington National Airport said the airport is expected to be closed July 4, with no scheduled flights after noon, citing the flyovers and other aerial displays.

The celebration faces an additional challenge: extreme heat. The predicted high for Saturday in Washington is 101 degrees, according to The Weather Channel. A Freedom 250 representative said there will be four free hydration stations and that organizers were “closely monitoring conditions.”

Vitale said the goal is to create a lasting memory. “Size always helps, but it’s about the beauty and the memories that people will have for generations,” he said. “Fireworks are magical to people, and we help people walk away believing that’s the best fireworks display that they have seen or ever will see.”