September in Valparaiso is the coldest month of the year. In September, the weather in Valparaiso is typically warm. Average daily high temperature in September is about 12 degrees above zero. On average, Valparaiso has 15 sunny, 9 partly cloudy, 4 rainy, and 2 cloudy days in September. The rains are usually moderate. September as well as June, July, and August is considered the most uncomfortable time to visit Valparaiso.