In September, the weather in Invercargill is typically warm. Average daily high temperature in September is about 11 degrees above zero. On average, Invercargill has 23 rainy, 4 sunny, 2 cloudy, and 1 partly cloudy day in September. The rains are usually heavy. September as well as January, March, April, and May is considered the most uncomfortable time to visit Invercargill.