September in Mainz averages a daily high of 20.8°C with nights around 11.4°C. Expect roughly 9.4 wet days totalling 48.4mm. Comfortable conditions for being outdoors all day.
Across the year, the best time to visit Mainz is May–September.
Based on MAINZ LERCHENBERG ZDF, GM (5.1km), 1995–2024. 29 years of September data.