May in Siem Reap is the rainiest and the cloudiest month of the year. In May, the weather in Siem Reap is typically hot. Average daily high temperature in May is about 31 degrees above zero. On average, Siem Reap has 31 rainy days in May. The rains are usually heavy. May as well as April, June, July, and August is considered the most uncomfortable time to visit Siem Reap.