August in Sitka is the warmest month of the year. In August, the weather in Sitka is typically warm. Average daily high temperature in August is about 13 degrees above zero. On average, Sitka has 29 rainy, 1 sunny, and 1 cloudy day in August. The rains are usually heavy. August as well as January, February, March, and April is considered the most uncomfortable time to visit Sitka.