Emergency officials across the southeast United States were closely watching Irene on Tuesday as the first hurricane to seriously threaten the country in three years churned over energizing tropical waters. The storm has already cut a destructive path through the Caribbean. Forecasters say the hurricane could grow to a monstrous Category 4 storm with winds of more than 131 mph before it’s predicted to come ashore this weekend on the U.S. mainland. The National Hurricane Center in Miami expected Irene to reach Category 3 strength on Tuesday, said spokesman Dennis Feltgen.