US President Donald Trump will head to the National Mall in Washington DC on Saturday for what he called a “spectacular rally” to celebrate the 250th anniversary of the United States.

The event, taking place as a sweltering heat wave grips parts of the eastern and central United States, will include flyovers by hundreds of aircraft and a fireworks display that organizers hope will be the largest of all time.

Military flyovers over Washington DC will take place every hour between 1:15 p.m. local time (17:15 GMT) and sunset, organizers said, and Trump’s new Air Force One will feature in one of the formations over the capital.

The president, however, has been accused by his opponents of politicizing the nation’s anniversary event and several musical acts dropped out shortly after being announced.

Extremely hot and humid temperatures of approximately 100°F (38°C) and a later than expected start time may also have an impact on the size of the crowd attending.

The intense heat has already caused the cancellation of events. On Friday, organizers of the National Park Service Independence Day Parade in Washington, D.C., said they had canceled the annual event over safety concerns. Some celebration events have also been canceled from New Jersey, Pennsylvania and Maryland to western Colorado.

There is also the possibility of overnight storms that could disrupt the events, which have been organized by a public-private partnership backed by the White House.

President Trump used a speech on the eve of Independence Day to claim that American identity is threatened by what he called domestic “radicals” and “extremists.”

Speaking at the Mount Rushmore National Memorial in South Dakota on Friday, the president warned of a resurgence of what he called “the communist threat” and “newcomers” who embraced ideas opposed to the American way of life.

His comments reflect a growing line of political attack ahead of November’s midterm elections, in which Republicans seek to brand Democrats as communists.

The event in Washington DC, formally known as the Salute to America 250 Celebrations & Fireworks, will begin at 7:00 p.m. local time, with Trump expected to speak a few hours later, at approximately 9:45 p.m.

He promised to give a “really long speech” at the Fourth of July festivities, despite the heat wave, “to show that I can do anything.”