Hurricane Gloria, at times packing winds of more than 150 miles per hour, yesterday turned into the mightiest storm tracked across the open Atlantic in more than 30 years. The storm was moving northwest on a path that could take it across Cape Hatteras, N.C., or aim it toward eastern Long Island and the New England states of Rhode Island and Massachusetts.

Last night, Gloria measured 300 miles across and was located about 460 miles south-southeast of Cape Hatteras, moving at 15 mph and forcing the evacuation of some islands along North Carolina's Outer Banks. In coastal Dare and Carteret counties, 47,000 residents were warned that they should seek shelter.

In Norfolk, Va., and Charleston, S.C., all Navy ships were ordered to leave for safe anchorages at sea. Navy pilots in Tidewater Virginia made plans to fly aircraft to Wright-Patterson Air Force Base in Dayton, Ohio, for refuge, officials said.

A hurricane watch was posted from Charleston to Cape Henry, Va., although forecasters said they expect Gloria to turn to the northeast and possibly bring Gloria ashore in New England.

"Anyone who lives along the East Coast should pay close attention to this storm," said Dr. Neil Frank, director of the National Hurricane Center outside Miami. "This is a dangerous hurricane and people from the Carolinas to New England should closely monitor the progress of this storm."

Mark Zimmer, of the National Hurricane Center, rated Gloria a "strong" Category 4 storm based on a scale of 1 to 5; for a brief time yesterday morning, Gloria reached winds of 156 miles an hour that put it in Category 5.

"The only Category 5 storms to hit the United States in this century were Camille in 1969 and the 1935 hurricane that tore up the Florida Keys so bad they had to rebuild the railroad," Zimmer said. "What we want to emphasize about Gloria is that it's a very dangerous hurricane, regardless of whether it's a 4 or a 5.

"The winds may vary from 145 to 155 miles an hour but if you get hit with those winds you're not going to notice the difference," he said.

Hurricane watchers said Hurricane Gloria had a large, well-defined eye at least 12 miles across that suggested it carried stronger and more damaging winds than most tropical storms.

One weather expert pointed out that Gloria has been gathering strength in the warm waters of the south Atlantic for a longer period than most tropical storms.

"Tropical storms are like alligators," Don Gilman, of the Climate Analysis Center in Rockville, said. "The older they get, the bigger they get."

Forecasters were reluctant last night to predict where Gloria would touch land or what direction the storm would take. Although warnings for the Bahamas were lifted at noon, forecasters said Hurricane Gloria did not make an expected turn to the northeast, making their job of predicting that turn more difficult than it already was.

"This storm is now embedded in the prevailing steering winds that dominate the East Coast this time of year," said Dr. Richard Anthes of the National Center for Atmospheric Research and author of a book on hurricanes.

"Those steering winds are south to southwest, which means they should soon carry the storm on a north-to-northeast path that takes it very close to the coastal states of New England," he said.

Anthes said the next 24 hours are crucial to the storm's progress. The hurricane could weaken, its forward speed slow down and its direction change -- all at once. Or Gloria could gather strength, move even at a faster forward speed and not change direction at all.

"It's almost impossible to predict when these things might happen," Anthes said. "Hurricanes are very unpredictable beasts."

Anthes said Gloria comes as something of a surprise to hurricane watchers, who have seen hurricanes move away from the Atlantic states to the states bordering the Gulf of Mexico.

"Far fewer storms have hit the East Coast since the '50s," Anthes said. "We don't precisely know why this is the case but it seems that the steering winds that direct the movement of tropical storms have themselves changed in the last 30 years."

Frank also pointed out that hurricanes often pick up speed as they move north over colder water, meaning that Gloria "could weaken to a Category 3 storm moving at 50 miles an hour that could do just as much damage as a Category 5 storm moving along at 15 miles an hour."

Other hurricane watchers cautioned that Gloria might cross the warm waters of the Gulf Stream, which would provide fresh fuel for the storm's internal engine. If that happened, Gloria could strike in full fury, sustaining its 150 mph winds to landfall.

"What's important here is that the storm is over the open sea," Gilman said. "Storms like this that stay over open water can be very explosive."

As campers began to evacuate the remote islands of the Outer Banks, Jan Price of the National Weather Service in Raleigh, N.C., said the "critical thing here is how soon this storm begins to turn northward."

Along the coast, disaster officials were making "get ready" plans and hoping for the best. John Doyle, of the South Carolina emergency preparedness office, said, "We're setting up duty rosters for what could be a long weekend."