September in San Juan del Rio is the cloudiest month of the year. In September, the weather in San Juan del Rio is typically warm. Average daily high temperature in September is about 18 degrees above zero. On average, San Juan del Rio has 24 rainy, 3 cloudy, 2 sunny, and 1 partly cloudy day in September. The rains are usually heavy. September as well as July and August is considered the most uncomfortable time to visit San Juan del Rio.