Hurricane Bill became a dangerous Category 4 storm Wednesday as it howled through the open Atlantic's energizing waters, which could further boost the storm's power as it moves north.

Forecasters said Bill should begin pushing large swells toward Bermuda and parts of the southeastern U.S. coast by the weekend, but it wasn't yet clear how close the storm will come to land.

The National Hurricane Center also said people in the Leeward Islands should keep an eye on the storm, though its core was expected to pass well to the northeast of the chain in the next 24 hours. Fishermen in Antigua were advised to dock their boats.

"The wind shear is light and the waters are warm," Todd Kimberlain, a forecaster at the center, said Tuesday. "Those are two essential ingredients not just for the formation, but also the maintenance, of hurricanes."

Bill was maintaining a top wind speed of 135 mph Wednesday, and forecasters said it could get stronger. The storm's center was located 380 miles east of the Leeward Islands — or more than 1,500 miles southeast of Miami — and it was moving west-northwest near 18 mph.

The most significant threat could be to Bermuda, which the storm could pass in three or four days, Kimberlain said. But it also could move directly between Bermuda and the eastern coast of the U.S. without making landfall.

Regardless of how close Bill comes to land, it should begin sending stronger waves toward Bermuda and parts of the southeastern U.S. coast Friday and Saturday, hurricane specialist Eric Blake said.

It was too early to tell if Bill would veer close to shore over the weekend or swing away from the East Coast of the U.S., but the five-day forecast predicted its center would pass well offshore of the North Carolina-Virginia line Sunday.

A cold front was expected to turn Bill to the northeast, but it wasn't clear when that would happen, Blake said.

Source: AP