August in Phonsavan is the rainiest month of the year. In August, the weather in Phonsavan is typically warm. Average daily high temperature in August is about 26 degrees above zero. On average, Phonsavan has 30 rainy and 1 partly cloudy day in August. The rains are usually heavy. August as well as April, May, June, and July is considered the most uncomfortable time to visit Phonsavan.