September in Whyalla is the windiest month of the year. In September, the weather in Whyalla is typically warm. Average daily high temperature in September is about 20 degrees above zero. On average, Whyalla has 21 sunny, 8 partly cloudy, and 1 rainy day in September. The rains are usually light. September as well as March, April, October, and November is considered the most comfortable time to visit Whyalla.