September in Gustavia is the hottest month of the year. In September, the weather in Gustavia is typically hot. Average daily high temperature in September is about 29 degrees above zero. On average, Gustavia has 13 rainy, 11 sunny, 5 partly cloudy, and 1 cloudy day in September. The rains are usually moderate. September as well as August, October, and November is considered the most uncomfortable time to visit Gustavia.