August in Koumac is the sunniest month of the year. In August, the weather in Koumac is typically warm. Average daily high temperature in August is about 23 degrees above zero. On average, Koumac has 17 sunny, 7 partly cloudy, 5 rainy, and 2 cloudy days in August. The rains are usually moderate. August as well as June, July, and September is considered the most comfortable time to visit Koumac.