September in Harbour Island is the rainiest month of the year. In September, the weather in Harbour Island is typically hot. Average daily high temperature in September is about 28 degrees above zero. On average, Harbour Island has 20 rainy, 7 sunny, and 3 partly cloudy days in September. The rains are usually heavy. September as well as June, July, August, and October is considered the most uncomfortable time to visit Harbour Island.