September in Mount-Hagen is the warmest month of the year. In September, the weather in Mount-Hagen is typically warm. Average daily high temperature in September is about 18 degrees above zero. On average, Mount-Hagen has 29 rainy and 1 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 Mount-Hagen.