September in Riobamba is the warmest month of the year. In September, the weather in Riobamba is typically warm. Average daily high temperature in September is about 11 degrees above zero. On average, Riobamba has 20 rainy, 9 cloudy, and 1 sunny 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 Riobamba.