Tropical Storm Irene (search) strengthened into a hurricane Sunday, but turned away from the East Coast and posed no threat to land, forecasters said.

Hurricane Irene (search) had top sustained winds of 80 mph, just above the 74 mph threshold to become a hurricane.

At 11 p.m. EDT, Irene was about 355 miles east of Cape Hatteras, N.C., and 325 miles northwest of Bermuda, according to the National Hurricane Center (search) in Miami. It was moving north-northeast at 9 mph and was expected to turn northeast.

Elsewhere, the Atlantic hurricane season's 10th tropical depression was poorly organized and appeared to be dissipating, just a day after it developed. The depression was more than 1,000 miles east of the Leeward Islands, with 30 mph sustained winds.

Normally, there are only two or three named storms by this time in the Atlantic hurricane season, which began June 1 and ends Nov. 30.