SAN JUAN, Puerto Rico — Tropical Storm Rafael strengthened into a Category 1 hurricane on Tuesday as it swirled past Jamaica and barreled toward western Cuba.It was another stroke of bad news for Cuba, which has been struggling with blackouts while recovering from another hurricane two weeks ago that killed at least six people in the eastern part of the island.The storm was located 20 miles southeast of Little Cayman in the Cayman Islands on Tuesday morning. It had maximum sustained winds of 75 mph and was moving northwest at 15 mph, according to the National Hurricane Center in Miami.Forecasters warned that Rafael was expected to slam into the island on Wednesday after dumping rain on Jamaica and the Cayman Islands on Tuesday. The center warned of floods and mudslides.