NAGS HEAD, N.C. — Hurricane Earl steamed toward the Atlantic Seaboard on Wednesday as communities from North Carolina to New England kept a close eye on the forecast, worried that even a slight shift in the storm’s predicted offshore track could put millions of people in the most densely populated part of the country in harm’s way.

Vacationers along North Carolina’s dangerously exposed Outer Banks took advantage of the typical picture-perfect day just before a hurricane arrives to pack their cars and flee inland, cutting short their summer just before Labor Day weekend.

The governors of North Carolina, Virginia and Maryland declared a state of emergency, sea turtle nests on one beach were scooped up and moved to safety, and the crew of the Navy’s USS Cole rushed to get home to Norfolk, Va., on Wednesday ahead of the bad weather. The destroyer was supposed to return from a seven-month assignment later this week.

Farther up the East Coast, emergency officials urged people to have disaster plans and supplies ready and weighed whether to order evacuations as they watched the latest maps from the National Hurricane Center — namely, the “cone of uncertainty” showing the broad path the storm could take.

Earl was expected to reach the North Carolina coast late Thursday and wheel to the northeast, staying offshore while making its way up the Eastern Seaboard. But forecasters said it could move in closer, perhaps coming ashore in North Carolina, crossing New York’s Long Island and passing over the Boston metropolitan area and Cape Cod.

That could make the difference between modestly wet and blustery weather on the one hand, and dangerous storm surge, heavy rain and hurricane-force winds on the other.

“Everyone is poised and ready to pull the trigger if Earl turns west, but our hope is that this thing goes out to sea and we’re all golfing this weekend,” said Peter Judge, a spokesman for the Massachusetts Emergency Management Agency.

As of Wednesday afternoon, Earl was a Category 3 hurricane centered more than 680 miles southeast of Cape Hatteras, with winds of 125 mph. Forecasters said it was strengthening and could become a Category 4 later in the day with winds of 131 mph or more.

The only evacuations ordered were on Hatteras and Ocracoke Islands, part of the Outer Banks. Just a light breeze was stirring and there wasn’t a cloud in the sky along the Outer Banks — a ribbon of barrier islands a dozen miles or more off the mainland, connected to the rest of the world by a couple of bridges and a ferry. Along the lone highway, hundreds of cars backed up at one of the bridges.

Brittany Grippaldi and her family took advantage of the good weather to pack up their Ford Explorer in Hatteras and head home to New Jersey.

“It’s sad because reality hasn’t really set in because it is so beautiful out. It’s like, ‘Oh, I don’t want to leave this,’ but it’s like the calm before the storm,” said Grippaldi, who hoped to beat the traffic.

Chuck Costas also wasn’t taking any chances, interrupting his two-week vacation to move inland from the cottage he rented on Nags Head. Large waves already crashing ashore uncomfortably close to the home.

“It is what it is,” he said. “We have no control over it. If we lose a couple days, it’s not a huge loss.”

Hurricane warnings were posted for most of the North Carolina coast, with a hurricane watch extending to Delaware.

In Virginia, Gov. Bob McDonnell activated the National Guard and sent 200 troops to the Hampton Roads area on Chesapeake Bay. The area was not expected to get the brunt of Earl, but many remember the surprise fury of Hurricane Isabel, which killed 33 people and did $1.6 billion in damage in September 2003.

“I’d rather be safe and get our troops and state police in place by Thursday night,” the governor said.

Emergency officials on Cape Cod braced for their first major storm since Hurricane Bob brought winds of up to 100 mph to coastal New England in August 1991. Marinas encouraged people to take their boats out of the water now instead of waiting for Labor Day.