A tropical storm moving towards north along the Central America has unleashed heavy rains that have killed at least eight people in Costa Rica and Nicaragua. Forecasters predict it could strengthen into a hurricane headed for the United States. <br/><br/>Costa Rica has declared a national emergency as it struggled with mudslides, washed out roads and overflowing rivers. Schools, universities, government offices and state banks across the Central American nation have been closed. <br/><br/>Officials in Costa Rica said six people died: four Costa Ricans – including a three-year-old girl – hit by falling trees and mudslides, and two young Nicaraguan farm workers. At least 15 people were missing. In neighbouring Nicaragua, two people died, and seven people were missing, Vice President Rosario Murillo told state media.