September in Blackheath is the windiest month of the year. In September, the weather in Blackheath is typically warm. Average daily high temperature in September is about 17 degrees above zero. On average, Blackheath has 20 sunny, 7 partly cloudy, and 3 rainy days in September. The rains are usually light. September as well as April and October is considered the most comfortable time to visit Blackheath.