Authorities in Guam warned anyone not living in a fully concrete house to head to safety elsewhere, and emergency shelters began to fill as residents braced for Typhoon, a powerful storm that could deliver the biggest hit in two decades to the U.S. territory in the Pacific. Gov. Lou Leon Guerrero urged residents in a YouTube message to remain calm and prepare for Mawar, which the National Weather Service said could hit southern Guam around midday Wednesday.