In September, the weather in Cao Bằng is typically hot. Average daily high temperature in September is about 27 degrees above zero. On average, Cao Bằng has 22 rainy, 4 sunny, 2 cloudy, and 2 partly cloudy days in September. The rains are usually heavy. September as well as May, June, July, and August is considered the most uncomfortable time to visit Cao Bằng.