September in Skien averages a daily high of 17.2°C with nights around 8°C. Expect roughly 13.6 wet days totalling 104.1mm. Generally workable, with some weather to plan around.
Across the year, the best time to visit Skien is June–September.
Based on GVARV NES, NO (30.1km), 1995–2024. 28 years of September data.