September in Kotka averages a daily high of 15.2°C with nights around 10.5°C. Expect roughly 10.2 wet days totalling 46.9mm. Generally workable, with some weather to plan around.
Across the year, the best time to visit Kotka is June–August.
Based on KOTKA RANKKI, FI (10.2km), 1995–2024. 29 years of September data.