In September, the weather in Waikoloa is typically warm. Average daily high temperature in September is about 23 degrees above zero. On average, Waikoloa has 21 partly cloudy, 6 sunny, 2 cloudy, and 1 rainy day in September. The rains are usually light. September as well as January, February, April, and May is considered the most comfortable time to visit Waikoloa.