NASSAU (Reuters) - Hurricane Irene strengthened to a major Category 3 hurricane over the Bahamas on Wednesday as it roared up from the Caribbean on a path expected to swipe the US East Coast from the Carolinas upward at the weekend.Irene, the first hurricane of the 2011 Atlantic season and the first this year to seriously threaten the United States, was expected to intensify further over the coming days as it swept over the low-lying Bahamas. The US National Hurricane Center warned of an “extremely dangerous” storm surge.Forecasters see Irene striking North Carolina's Outer Banks region on Saturday afternoon and then taking a coast-hugging track up the US mid-Atlantic and New England coastline.At 8am EDT (noon GMT), Irene was carrying winds of 115 miles per hour and was located about 55 miles (85 km) southeast of Acklins Island in the Bahamas and about 335 miles (540 km) southeast of Nassau, the capital of the Atlantic archipelago southeast of Florida, the Miami-based NHC said.The wind speed made it a major Category 3 hurricane on the five-step Saffir-Simpson intensity scale, posing a high risk of injury and death from flying and falling debris.See The Royal Gazette's Stormwatch page for more information.