RODANTHE, N.C. — Arthur strengthened to a hurricane early today and threatened to give North Carolina a glancing blow on Independence Day, prompting the governor to warn vacationers along the coast not to risk their safety by trying to salvage their picnics and barbecues.

Forecasters expect Arthur to whip past the state’s Outer Banks on Friday without making landfall. One local remarked that he was more worried about his tomato plants than storm damage.

But North Carolina Gov. Pat McCrory warned: “Don’t put your stupid hat on.”

The first named storm of the Atlantic hurricane season prompted a hurricane warning for much of the North Carolina coast and a mandatory evacuation for visitors to the Outer Banks’ Hatteras Island as of 5 a.m. today. Residents also were advised to leave the island. A voluntary evacuation was announced for the Outer Banks’ Ocracoke Island, accessible only by ferry.

The islands are linked by North Carolina Route 12, which has been sliced apart twice in recent years as storms cut temporary channels from the ocean to the sound. Hatteras Island is particularly vulnerable to storm surge and flooding. In addition to the hurricane warning, tropical storm warnings were in effect for coastal areas in South Carolina and Virginia.

Gary Reinhardt, 63, and his wife Lori, both of Sarasota, Fla., said they planned to exit low-lying Hatteras Island this morning. A long line of cars, trailers and recreational vehicles already formed a steady stream of traffic before sunset Wednesday.

“I’m worried about the road. It took way too long to get here,” said Gary Reinhardt, adding that the two-and-a-half-hour delay to get on the island came Sunday, when there was no hurricane threatening. Reinhardt worried their departure would take twice as long today.

Mike Rabe of Virginia Beach, Va., planned to stay in his beach home the entire weekend. He and his wife, Jan, arrived Wednesday at the house they bought two and a half years ago and set to work stowing lawn furniture and anything else that could be tossed about by the wind. He said he was going to spend today helping a friend prep his shop for bad weather.

“I’m going to help him prepare and then I’m going to ride it out,” said Rabe, 53.

Other areas of the Outer Banks were taking a cautious, but still-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 December 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.

In the Myrtle Beach area, the heart of South Carolina’s $18 billion tourism industry, Arthur was expected to move by tonight, spinning wind gusts from 40 to 50 mph toward the high-rise hotels and condominiums lining the oceanfront.