September in Bonn averages a daily high of 20.2°C with nights around 10.5°C. Expect roughly 11.8 wet days totalling 61.6mm. Comfortable conditions for being outdoors all day.
Across the year, the best time to visit Bonn is May–September.
Based on BONN ROLEBER, GM (6.9km), 1995–2024. 25 years of September data.