September in Bangkok is the rainiest month of the year. In September, the weather in Bangkok is typically hot. Average daily high temperature in September is about 32 degrees above zero. On average, Bangkok has 26 rainy, 2 cloudy, 1 sunny, and 1 partly cloudy day in September. The rains are usually heavy. September as well as April, May, June, and July is considered the most uncomfortable time to visit Bangkok.