Hurricane Gonzalo strengthened to become a major Category 3 hurricane on Tuesday as it moved away from the northern Caribbean and headed toward Bermuda, 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 further north into the Atlantic. It could hit Bermuda late on Friday, and the island was put under a hurricane watch.

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 705 miles (1,135 km) south of Bermuda late on Tuesday and packed sustained winds reaching 125 miles per hour (205 km per hour), 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 Oct. 2, 2011," when Hurricane Ophelia's winds reached 140 mph (225 kph), according to Jeff Masters, a hurricane expert with private forecaster Weather Underground.

Gonzalo would likely begin weakening by late on 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 (48 to 129 km) 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.