RODANTHE, N.C. – Arthur strengthened to a hurricane early Thursday and threatened to upend Americans’ plans for Friday’s Independence Day up and down the East Coast.

North Carolina braced itself for a glancing blow ahead of the holiday, prompting the governor of the southern state to warn vacationers along its coast not to risk their safety by trying to salvage their picnics and barbecues.

The National Hurricane Center predicted Arthur would swipe the coast early Friday with winds of up to 85 mph (136 kph). The storm would be off the coast of New England later Friday and eventually make landfall in Canada’s maritime provinces as a tropical storm, the Hurricane Center predicted.

Up north in Boston, one of America’s signature Fourth of July events, the annual Boston Pops outdoor concert and fireworks show, was moved up a day because of potential heavy rain ahead of the hurricane.

The performance takes place along the Charles River Esplanade, with fireworks set off from barges on the river. Hundreds of thousands of people usually attend. Organizers and public safety officials said the celebration was rescheduled for Thursday, which appeared to be the best of two potential bad weather days.

Arthur, the first named storm of the Atlantic season, prompted a hurricane warning for much of the North Carolina coast. Tropical storm warnings were in effect for coastal areas in South Carolina and Virginia.

Forecasters expect Arthur to whip past the North Carolina’s Outer Banks islands on Friday without making landfall, but Gov. Pat McCrory warned vacationers along the coast not to risk their safety by trying to salvage their picnics, barbecues and pre-paid beach cottage vacations.

“Don’t put your stupid hat on,” McCrory said.

On the Outer Banks’ Ocracoke Island, accessible only by ferry, a voluntary evacuation was underway. A mandatory evacuation for Hatteras Island visitors began at 5 a.m.

Outer Banks residents and out-of-town visitors who fail to evacuate ahead of the hurricane’s expected arrival should prepare for possibly getting stuck for several days without food, water or power, National Hurricane Center forecaster Stacy Stewart said Thursday.

“We want the public to take this system very seriously, go ahead and start their preparations because time is beginning to run out,” he said.

Before sunset Wednesday on Route 12, which links North Carolina’s coast and some of the Outer Banks islands, a long line of vehicles formed a steady stream of traffic. The road has been sliced apart twice in recent years as storms cut temporary channels from the ocean to the sound. The road is easily blocked by sand and water.

Other areas of the Outer Banks were taking a cautious yet optimistic approach: No evacuations had been ordered for areas north of Hatteras, including the popular town of Kill Devil Hills, which was the site of the Wright brothers’ first controlled, powered airplane flights in 1903.

The holiday weekend was not expected to be a complete loss for the estimated quarter-million visitors vacationing on the Outer Banks. Forecasters said the storm would move through quickly with the worst of the weather near Cape Hatteras about dawn Friday. Then it was expected to clear.

On Thursday morning, Arthur was about 300 miles (480 kilometres) southwest of Cape Hatteras and moving north around 9 mph (15 kph) with maximum sustained winds of 80 mph (130 kph).