Ship Trap Island is in South America, specifically in the "blood warm waters of the Caribbean sea". Such a setting is both ominous and exotic, which sets the readers up for a story that will both surprise and scare them.
The sea is surrounded by small and large islands to the east and North, and by Central and South America to the west and south. It almost appears as an enclosed and circular sea, with Cuba its north boundary, Mexico its west boundary, Venezuela is south boundary, and the Virgin Islands its east boundary. The waters of the Caribbean are warm and a clear, pale blue in color. The sea is home to about 29% of the world's coral reefs, giving the impression that there are islands beneath the surface of the water.
Below is a link to a good map of the Caribbean Sea.