September in New Ulm is the sunniest month of the year. In September, the weather in New Ulm is typically warm. Average daily high temperature in September is about 23 degrees above zero. On average, New Ulm has 15 sunny, 8 rainy, 6 partly cloudy, and 1 cloudy day in September. The rains are usually heavy. September as well as January is considered the most comfortable time to visit New Ulm.