MIAMI (Reuters) - Hurricane Earl weakened slightly to a Category 3 storm as it churned toward the eastern U.S. seaboard on Wednesday and looked to sideswipe the densely populated coast from North Carolina to New England, the U.S. National Hurricane Center said.
Forecasters expected the main core of the hurricane to stay offshore as Earl moved north parallel to the coast during the upcoming Labor Day holiday weekend that traditionally marks the end of summer.
Earl's top sustained winds slowed somewhat to 125 mph, making it a Category 3 storm on the five-step Saffir-Simpson intensity scale, the NHC said.
"Some fluctuations in strength are possible during the next 48 hours," the center said.
A hurricane watch was extended northward along the Virginia coast and officials warned that any westward deviation from the forecast track could prompt coastal evacuations or even bring the storm ashore.
"A small error of 100 miles in the wrong direction could be a huge impact difference," National Hurricane Center Director Bill Read told a conference call with journalists.
"Even a minor shift back to the west could bring impacts to portions of the coastline from the mid-Atlantic northwards."
The hurricane watch, issued by the Miami-based hurricane center, alerts residents that hurricane conditions -- sustained winds of 74 mph -- are possible within 48 hours.
Earl, the second major hurricane of the 2010 Atlantic season, was moving northwest in the open Atlantic at nearly 16 mph north of Gran Turk Island.
At 5 a.m. (0900 GMT), it was centered about 815 miles south-southeast of Cape Hatteras, North Carolina.
On the forecast track, the hurricane will pass well east and northeast of the Bahamas on Wednesday and could approach the North Carolina coast by Friday morning, the NHC said.
Earl was forecast to bring drenching rain, rough seas, pounding surf and gusting wind to the Atlantic Coast from North Carolina to New England and Atlantic Canada.
Evacuations were ordered, or expected, for Wednesday for the most vulnerable spots on the Outer Banks, including the Cape Lookout National Seashore and Ocracoke Island, which has about 800 year-round residents and is accessible only by boat. It is one of the barrier islands where the pirate Blackbeard once roamed.
SOME UNCERTAINTY OVER FINAL PATH
It was too early to predict how close the hurricane would come to New York when it churned offshore east of the city during the weekend.
"We're just telling everybody to keep their eyes on the track and just keep checking back," hurricane center meteorologist Barry Baxter said.
The hurricane center said Earl's forecast track in the coming days shifted slightly to the west, which could bring its outer fringes closer to the U.S. coast.
U.S. and Canadian East Coast oil refiners said they were monitoring Earl but that it was too early to begin to take any precautionary measures.
Hurricane Earl posed no threat to major U.S. oil and gas installations in the Gulf of Mexico.
Tropical storm warnings and watches were in effect for the Turks and Caicos, where flights were suspended, and for the sparsely populated southeast Bahamas.
On Monday, Earl battered the northeastern Caribbean islands and Puerto Rico, downing power lines, blowing off roofs, toppling trees and causing some flooding. There were no immediate reports of casualties.
(Additional reporting by Gene Cherry in Raleigh, Tom Brown, Kevin Gray and Pascal Fletcher in Miami and Eileen Moustakis in New York; editing by Anthony Boadle)
