September in Milford Sound is the cloudiest month of the year. In September, the weather in Milford Sound is typically cold. Average daily high temperature in September is about 6 degrees above zero. On average, Milford Sound has 23 rainy, 4 sunny, 2 cloudy, and 1 partly cloudy day in September. The rains are usually heavy. September as well as January, February, March, and April is considered the most uncomfortable time to visit Milford Sound.