In September, the weather in Bandar Seri Begawan is typically hot. Average daily high temperature in September is about 30 degrees above zero. On average, Bandar Seri Begawan has 27 rainy, 2 cloudy, and 1 sunny day in September. The rains are usually heavy. September as well as January, February, March, and April is considered the most uncomfortable time to visit Bandar Seri Begawan.