Gonzalo becomes major hurricane over open Atlantic waters

SAN JUAN Puerto Rico (Reuters) - Hurricane Gonzalo strengthened to become a major Category 3 hurricane on Tuesday as it moved over the open Atlantic waters and swirled away from the northern Caribbean islands, the U.S. National Hurricane Center said.

The center of Gonzalo was moving northwest, away from the British and U.S. Virgin Islands and Puerto Rico, prompting storm alerts for those areas to be lifted.

Most forecasts showed Gonzalo posing no threat to the mainland United States and moving still further north into the Atlantic. It could hit Bermuda late on Friday.

Gonzalo is the sixth hurricane of the 2014 Atlantic hurricane season, which runs through the end of November. Forecasters in August predicted lower than usual activity for the season, with seven to 12 named storms and no more than two reaching major hurricane status.

Gonzalo was about 770 miles (1,240 km) south of Bermuda and packed sustained winds reaching 115 mph (185 kph) on Tuesday, the center said.

A major hurricane is considered to be Category 3 or above with winds hitting at least 111 mph (178 kph).

"Gonzalo has a good chance of becoming the Atlantic's first Category 4 hurricane since October 2, 2011," when Hurricane Ophelia reached 140 mph (225 kph) winds, according to Jeff Masters, a hurricane expert with private forecaster Weather Underground.

Gonzalo would likely begin weakening by late Thursday, but could still reach Bermuda "anywhere between a Category 1 and Category 3 storm," he wrote in a blog post.

Forecast models showed it passing within 30 to 80 miles of the island on Friday.

The Virgin Islands and Puerto Rico experienced only light to moderate rain and wind gusts on Tuesday, and no significant damage or loss of power was reported.

Public schools were ordered closed for Tuesday in the eastern portion of Puerto Rico, but officials emphasized the move was precautionary. Public schools remained open elsewhere, and government offices were slated to be functioning normally throughout the island.

On Monday, Gonzalo's heavy rains and high winds destroyed several fishing boats, blew off roofs and downed power lines in Antigua and Barbuda.

Antiguan Prime Minister Gaston Browne ordered schools closed for a national cleanup effort on Tuesday to get the nation "fully back in business" by Wednesday.

(Reporting by Colleen Jenkins, David Adams, and Reuters in San Juan; Editing by Mohammad Zargham, Marguerita Choy and Cynthia Osterman)