September in Kenai is the rainiest month of the year. In September, the weather in Kenai is typically warm. Average daily high temperature in September is about 12 degrees above zero. On average, Kenai has 17 rainy, 6 sunny, 6 partly cloudy, and 1 cloudy day in September. The rains are usually heavy. September as well as May, August, October, and November is considered the most uncomfortable time to visit Kenai.