September in Hallettsville is the rainiest month of the year. In September, the weather in Hallettsville is typically hot. Average daily high temperature in September is about 30 degrees above zero. On average, Hallettsville has 16 sunny, 12 rainy, and 2 partly cloudy days in September. The rains are usually heavy. September as well as January, June, July, and August is considered the most uncomfortable time to visit Hallettsville.