September in Indianapolis is the sunniest month of the year. In September, the weather in Indianapolis is typically warm. Average daily high temperature in September is about 25 degrees above zero. On average, Indianapolis has 14 sunny, 8 rainy, 6 partly cloudy, and 2 cloudy days in September. The rains are usually heavy. September as well as {{month_nom: February}}, and {{month_nom: February}} is considered the most comfortable time to visit Indianapolis.