October in Portsmouth is the rainiest month of the year. In October, the weather in Portsmouth is typically warm. Average daily high temperature in October is about 14 degrees above zero. On average, Portsmouth has 13 rainy, 7 partly cloudy, 6 cloudy, and 5 sunny days in October. The rains are usually heavy. October as well as January, February, March, and April is considered the most uncomfortable time to visit Portsmouth.