September in Sihanoukville is the windiest and the coldest month of the year. In September, the weather in Sihanoukville is typically hot. Average daily high temperature in September is about 28 degrees above zero. On average, Sihanoukville has 30 rainy days in September. The rains are usually heavy. September as well as April, May, June, and July is considered the most uncomfortable time to visit Sihanoukville.