August in Koumac is the coldest month of the year. In August, the weather in Koumac is typically warm. Average daily high temperature in August is about 22 degrees above zero. On average, Koumac has 15 partly cloudy, 12 sunny, 3 rainy, and 1 cloudy day in August. The rains are usually light. August as well as May, July, September, and October is considered the most comfortable time to visit Koumac.