July 7 (Bloomberg) -- Bertha, the first hurricane of the 2008 Atlantic season, strengthened into a ``major'' Category 3 storm today east of the Leeward Islands.

Bertha intensified from tropical-storm levels last night and quickly grew to a maximum sustained wind speed of 115 mph (185 kph) as of 5 p.m. Miami time, the U.S. National Hurricane Center said in the latest advisory on its Web site. A tropical storm becomes a hurricane when sustained winds reach 74 mph.

If the storm moves as current computer models predict, it could threaten Bermuda, about 670 miles (1,078 kilometers) east of the North Carolina coast, by July 12.

The eye of the hurricane was about 730 miles east of the northern Leeward Islands, which include Antigua and St. Kitts, and 1,150 miles southeast of Bermuda, the hurricane center said in its 5 p.m. advisory. The storm was moving west-northwest at 12 mph, the center said.

``It is still way too soon to determine whether or not Bertha will affect Bermuda,'' according to the advisory. The storm is expected to fluctuate in strength, the center said.

The Atlantic hurricane season runs from June 1 to Nov. 30.

To contact the reporter on this story: Alex Morales in London at amorales2@bloomberg.net.

Last Updated: July 7, 2008 16:50 EDT