September in Belize City is the hottest month of the year. In September, the weather in Belize City is typically hot. Average daily high temperature in September is about 30 degrees above zero. On average, Belize City has 28 rainy and 2 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 Belize City.