Earl, the strongest Atlantic storm of 2010, was expected to remain offshore as it skirts the eastern seaboard beginning late Thursday.

The storm was on course to bring winds and rains to the coast of North Carolina and then move north, wreaking havoc on the end-of-summer Labor Day holiday weekend that usually draws millions to East Coast beaches.

With the Miami-based National Hurricane Center (NHC) predicting hurricane strength winds as far out as 90 miles (145 kilometers) from the eye of the storm, coastal North Carolina residents were battening down.

"We're already experiencing some higher surf conditions," said Cyndy Holda, public affairs officer at Cape Hatteras National Seashore in North Carolina's popular Outer Banks area.

While some storm-hardened residents were ignoring the evacuation orders, Chris Davidson said he planned to drive with his wife and two children about 100 miles inland, where his mother still lives.

"I'm probably going to leave town later this afternoon," Davidson, a hardware store manager, told AFP. "It seems like more people are taking it more seriously than in the past."

At 11:00 am (1500 GMT) Earl was about 300 miles (485) kilometers south of Cape Hatteras in the Outer Banks -- a narrow band of North Carolina barrier islands.

Despite a bright sunny day on the North Carolina coast, the powerful category four storm was heading north at around 18 miles (30 kilometers) per hour.

The NHC also issued a hurricane warning for coastal Massachusetts, including the popular retreat areas of Cape Cod, Nantucket and Martha's Vineyard.

Tropical storm warnings meanwhile were issues for points all along the US east coast, while President Barack Obama signed a disaster declaration for North Carolina, ordering federal assistance to support response efforts.

A storm surge was expected mid-afternoon Friday, flooding the sole roadway between Hatteras Island and the North Carolina mainland three to five feet (one to 1.5 meters) above ground level.

US officials ordered a mandatory evacuation for 30,000 residents and visitors of North Carolina's Hatteras Island -- a death knell to thousands of vacation plans for a few last carefree days at the beach before summer's end.

Davidson said vacationers were lamenting the premature end of their summer, but local business owners bemoaned lost revenue they had been counting on.

"It'll definitely hurt the local economy. This was a big weekend for the hotels, restaurants and other businesses, although for us, it could give us additional business once the storm is over, depending on how bad it is."

Forecasters were also closely tracking the path of Tropical Storm Fiona about 550 miles (850 kilometers) south of Bermuda, with wind speeds of up to 50 miles (85 kilometers) per hour.

Gaston, the fourth tropical storm to form in the Atlantic over the past two weeks, weakened Thursday to a tropical depression, the NHC said, much to the relief of aid officials worried it would plow directly over Haiti, still recovering from January's massive earthquake.

Davidson said Earl's unwelcome arrival had brought an unwelcome end to what had been a banner year for coastal North Carolina.

"It's been a better tourist season than usual," he said. "A lot of families are staying close, driving to the beach, sharing the cost of a beach house rental.

"A lot of businesses were depending on this weekend to finish the season strong," he said.

Meanwhile, a pilotless NASA aircraft was set to overfly Hurricane Earl on Thursday, in a scientific first to gather data about the potentially-deadly storm front bearing down on the US east coast.

After taking off from Edwards Air Force base in California, the converted Global Hawk drone plane will use a battery of instruments to study how hurricanes develop into awesome forces of nature.

"This is a real adventure for this airplane," said Commander Phil Hall, who will remotely control the plane from the military base near Los Angeles on the US West Coast.

"Going over a hurricane, for any airplane, is a bit risky, and we are kind of breaking a new frontier with this flight," he told AFP.