Hurricane Earl Strengthens to Category 4 Storm

Hurricane Earl strengthened to a Category 4 storm on a track forecast to take it by the U.S. East Coast later this week. It was joined in the Atlantic by Tropical Storm Fiona, which formed 900 miles to its east.

Fiona becomes the third storm churning in the Atlantic. Earl, with maximum sustained winds of 135 miles (215 kilometers) per hour, presents the most immediate threat to the U.S. Danielle was downgraded to a tropical storm and is forecast to be absorbed by a weather front in the North Atlantic.

“Along the mid-Atlantic and East Coast you basically have today, Tuesday, and Wednesday to prepare,” said Rick Knabb, hurricane expert for the Weather Channel in Atlanta. “It could still be a powerful hurricane, and even if it doesn’t come directly ashore it could be close enough for tropical storm- force winds.”

The storm is expected to be off the Delmarva Peninsula parallel with Washington at 2 p.m. Sept. 3, according to the hurricane center. It will then move north, passing New York and Boston before coming ashore in Canada Saturday. A previous forecast showed Earl passing the Northeast earlier in the day.

“This is a good time to remind everyone that the National Hurricane Center average track forecast errors are 200 to 300 miles at days 4 and 5,” according to the center’s own analysis. “Given this uncertainty it is too soon to determine what portion of the U.S. East Coast might see a direct impact.”

Washington, New York, Boston

The time period when the storm is expected to be passing Washington and New York falls within that error period, said Jim Rouiller, a senior energy meteorologist at Planalytics Inc, a commercial forecaster in Berwyn, Pennsylvania.

He said that margin error means the entire East Coast has to remain on guard.

“We’re so close to the coast now, all residents have to watch and be vigilant because once it comes it is going to come quick and it is going to come hard,” Rouiller said.

Hurricane-force winds extend as far as 70 miles out from the storm center and tropical storm-force winds as far as 200 miles, the center said. That’s about the distance from New York to Boston. The storm is expected to turn toward the U.S. mid- Atlantic coast tomorrow.

Threat to U.S.

Rouiller said the farther Earl moves west before turning north, the more likely the hurricane is to come ashore in the U.S. It is moving west-northwest at 15 mph.

Earl is now at the second-highest level on the five-step Saffir-Simpson scale. It was 110 miles northeast of San Juan, Puerto Rico. The hurricane has prompted warnings and watches through the islands of the Greater and Lesser Antilles chains.

Tropical storm warnings, meaning winds of at least 39 mph are possible, have been issued for Puerto Rico, the Turks and Caicos islands, the British Virgin Islands and the U.S. Virgin Islands. France will discontinue a hurricane warning for St. Martin and St. Barthelemy at 6 p.m. Miami time, according to the hurricane center.

The storm may generate a surge of 5 feet (1.5 meters) above normal tide levels and produce rainfall of 8 inches in the affected islands and 12 inches in isolated higher elevations, the hurricane center said.

Hovensa LLC’s St. Croix refinery in the U.S. Virgin Islands is operating while the island ports are shut as Earl passes to the east.

The refinery sends finished products including heating oil and gasoline to the U.S. Gulf and East coasts, according to the company’s website.

Fiona Moving West

Trailing Earl is Tropical Storm Fiona, which is located about 890 miles east of the Leeward Islands and is moving west at 24 mph, according to the hurricane center.

Fiona is the Atlantic’s sixth storm and the third to form in the past nine days, since the start of the most active part of the season. Forecasters are also watching a fourth system just off Africa.

“I think that people definitely realize now that we’re turning into a hyperactive season and the threats made before the season are starting to be realized,” Rouiller said.

Before the season, academic, government and commercial forecasters all predicted an above-average number of storms in 2010. A typical year has 11 storms with winds of at least 30 mph, according to the hurricane center.

It has been a year since the Atlantic had three named storms active at the same time, according to hurricane records.

Oil fell today from its highest price in more than a week as forecasts showed Earl would head northward and not toward the Gulf of Mexico. The Gulf is home to 31 percent of U.S. oil output and about 10 percent of natural gas production.

To contact the reporters on this story: Randall Hackley in Zurich at rhackley@bloomberg.net; Brian K. Sullivan in Boston at bsullivan10@bloomberg.net.

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