Hurricane Earl weakened to a Category 3 storm as it churned toward the U.S. Eastern Seaboard 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 parallel to the coast during the upcoming Labour Day holiday weekend that traditionally marks the end of summer.
A hurricane watch that had been effect for the North Carolina coast was extended to the Virginia coast early Wednesday as officials warned 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 centre, alerts residents that hurricane conditions - sustained winds of 119 km/h - are possible within 48 hours.
At 5 a.m. EDT Wednesday, Earl was located about 1,300 kilometres south-southeast of Cape Hatteras, N.C., and moving northwest at about 26 kilometres an hour.
Earl was forecast to clip the barrier islands of North Carolina's Outer Banks on Thursday night and bring drenching rain, rough seas, pounding surf and gusting wind to the Atlantic Coast from North Carolina to New England and Atlantic Canada.
The latest forecast from the Canadian Hurricane Centre says hurricane Earl continues on its projected track and is likely to affect Atlantic Canada by this weekend.
The centre says it's still too early to issue warnings or discuss potential effects in Atlantic Canada because the hurricane is still too far away.
The centre says Earl is expected to continue its northwestward track before heading more towards the north.
There continues to be a wide-range of predictions of where the storm could potentially make landfall, from Maine in the west to as far east as Newfoundland.
Seas affected by Earl are expected to enter Atlantic Canadian waters on Thursday.
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.
Earl's maximum sustained winds have decreased to near 205 km/h. But the National Hurricane Center said fluctuations in strength are possible over the next 48 hours.
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.
Tropical Storm Fiona followed in Earl's wake on a similar path, though farther east.
With files from CP and AP