HATTERAS ISLAND, N.C., (Reuters) – Hurricane Earl  strengthened yesterday, churning up dangerous swells,  forcing evacuations on some of North Carolina’s barrier islands  and prompting storm alerts along much of the U.S. East Coast.

Watches and warnings were posted along the Atlantic coast  for most of North Carolina, Virginia, Maryland, Delaware, New  Jersey, New York, Connecticut, Rhode Island and part of  Massachusetts, alerting residents that hurricane and tropical  storm conditions were possible within 36 to 48 hours.

Earl had sustained winds of 135 mph (215 kph) as it  barreled across the Atlantic, making it a powerful and  dangerous Category 4 storm on the five-step Saffir-Simpson  scale of intensity, the U.S. National Hurricane Center said.

While a direct U.S. landfall was not forecast, Earl was on  track to deliver a sidelong blow to the North Carolina coast  ahead of the Labor Day holiday weekend marking the end of the  summer vacation season.

The hurricane’s center is seen passing within 100 miles  (160 km) of the state’s Outer Banks barrier islands late today or early tomorrow. The islands jut out into the  Atlantic and are frequently smacked by hurricanes and storms.

Forecasters said a low-pressure trough moving out of the  southwest over the United States would push Earl to the  northeast today, keeping it off the U.S. Coast. But they  warned that any westward deviation from the forecast track  could bring the core of the storm over the coast.