WILMINGTON, N.C. — People stocked up on food, boarded windows and gassed up their cars Tuesday as Hurricane Irene threatened to become the most powerful storm to hit the East Coast in more than a decade.Water, bread and batteries disappeared from store shelves. Lines formed at the pump. From Florida to Maine, residents were told to brace for flash flooding and power outages.Hundreds of miles south, Irene swirled through the Caribbean, giving a glimpse of what was to come. Homes were inundated with water, residents took refuge in schools and churches, and more than a million people were without electricity. One woman was killed in Puerto Rico. Forecasters warned it could get worse: The storm was likely to strengthen into a Category 4 monster by the time it makes a landfall in the U.S. this weekend, most likely hitting North Carolina. Irene could crawl up the coast Sunday toward the Northeast region, where residents aren’t accustomed to such storms.Officials dusted off evacuation plans and readied for the first hurricane to threaten the U.S. in three years. It’s been more than a decade since the East Coast has been hit by a major hurricane, considered a Category 3 with winds of at least 111 mph.