By Jane Sutton
MIAMI (Reuters) - Powerful Hurricane Earl churned toward the eastern U.S. seaboard on Tuesday and took aim 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 Labor Day holiday weekend that traditionally marks the end of summer.
But 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."
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.
Earl had top sustained winds of 135 miles per hour, making it a Category 4 storm on the five-step Saffir-Simpson intensity scale. It was expected to stay just shy of a maximum Category 5.
A hurricane watch could be posted by Tuesday night for the mid-Atlantic coast, alerting residents to expect storm conditions within 72 hours, forecasters said.
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.
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.
PUERTO RICO MOSTLY SPARED
Earl, the second major hurricane of the 2010 Atlantic season, was moving west-northwest in the open Atlantic east of the Turks and Caicos Islands on Tuesday, the forecasters said.
At 11 a.m. (1500 GMT), it was centered about 205 miles east of Grand Turk Island in the Turks and Caicos, a British territory at the southern tip of the Bahamas. That was about 1,070 miles south-southeast of Cape Hatteras, North Carolina.
Tropical storm warnings and watches were in effect for the Turks and Caicos and the sparsely populated southeast Bahamas.
Hurricane Earl posed no threat to major U.S. oil and gas installations in the Gulf of Mexico.
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.
"We have been quite fortunate. We did not take a direct hit ... it was not as serious as it could have been," Puerto Rico Governor Luis Fortuno told CNN.
Tropical Storm Fiona followed in Earl's wake on a similar path, though farther east.
At 11 a.m. (1500 GMT), Fiona was 440 miles east of the Caribbean Leeward Islands on a course that was expected to take it northeast of those islands on Wednesday. Most forecast models kept Fiona far away from the Gulf of Mexico.
With sustained winds of 40 mph, Fiona was just barely a tropical storm and the much more powerful Earl was hindering Fiona's development. Earl churned up the seas and brought cold water to the surface, starving Fiona of the warm water needed for rapid strengthening.
The storms were 900 miles apart but Fiona was moving much faster. If Fiona closes the gap, high-level winds spiraling from the top of Earl could shear off and weaken Fiona, the hurricane center's Baxter said.
"If it gets really close, Earl could actually chew it up and just kind of kill it," he said.
Elsewhere in the Atlantic, a broad area of low pressure about 400 miles southwest of the Cape Verde Islands in the eastern Atlantic had only a 10 percent chance of becoming a tropical cyclone within 48 hours, the hurricane center said.
Early computer models showed that system moving mostly west in the Atlantic but toward South America, not the energy-rich Gulf of Mexico.
(For more information about hurricanes and weather models, see: http://www.nhc.noaa.gov/ and http://www.skeetobiteweather.com/)
(Additional reporting by Tom Brown and Pascal Fletcher in Miami and Eileen Moustakis in New York; editing by Pascal Fletcher and Mohammad Zargham)
