BOSTON — The annual Boston Pops July 4th outdoor concert and fireworks show, one of the city’s signature events, is being moved up a day because of potential heavy rain ahead of Tropical Storm Arthur.

The celebration is being rescheduled to what appears to be the better of two potential bad weather days, organizers and public safety officials said Wednesday afternoon.

The performance takes place in the Hatch Shell along the Charles River Esplanade, with fireworks set off from barges on the river. Hundreds of thousands of people usually attend.

“It’s not optimal. We wish it were, but we’ve got to deal with this,” state police Col. Timothy Alben said.

He said security arrangements are ready, since the public final rehearsal would have been held Thursday night anyway.

Alben said officials recognize that afternoon road closings ahead of the show will affect traffic on a work day. People were urged to use public transportation.

Alben said the performance could be canceled Thursday if the weather isn’t safe. He said because of performer contracts the concert cannot be pushed to Saturday, though the fireworks show perhaps could be.

If the celebration takes place on July 3, the fireworks will be streamed live for the first time starting at 8 p.m. on and . The webcast also will be available for 24 days on demand at .

The concert has been delayed in the past because of threatening weather during a performance, and the fireworks have been rescheduled.

Arthur is forecast to pass well east of New England beginning Friday night. Moisture bands ahead of the storm are expected to bring rain and thunderstorms.

Other Massachusetts communities also have rescheduled fireworks shows because of the weather.

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