September in Londonderry is the sunniest month of the year. In September, the weather in Londonderry is typically warm. Average daily high temperature in September is about 22 degrees above zero. On average, Londonderry has 14 sunny, 9 rainy, 5 partly cloudy, and 2 cloudy days in September. The rains are usually heavy. September as well as {{month_nom: February}}, and {{month_nom: February}} is considered the most comfortable time to visit Londonderry.