In September, the weather in Irkutsk is typically warm. Average daily high temperature in September is about 13 degrees above zero. On average, Irkutsk has 13 rainy, 10 sunny, 6 partly cloudy, and 1 cloudy day in September. The rains are usually moderate. September as well as January, February, April, and December is considered the most uncomfortable time to visit Irkutsk.