SAN JUAN, Puerto Rico (AP) -- Tropical Storm Omar drenched islands in the southeastern Caribbean on Tuesday, downing trees and blowing off part of a school's roof as it menaced U.S. islands.

Officials in Puerto Rico warned residents of the U.S. Caribbean territory, already soaked from several days of rain, to prepare for lots more. Medical authorities appealed for blood donations for possible casualties of the storm.

Omar's expected path could take it over Puerto Rico overnight Wednesday, or it could drift further east over the nearby U.S. and British Virgin Islands.