September in Oslo averages a daily high of 16.7°C with nights around 9°C. Expect roughly 11.1 wet days totalling 85.4mm. Generally workable, with some weather to plan around.
Across the year, the best time to visit Oslo is June–September.
Based on OSLO BLINDERN, NO (3.6km), 1995–2024. 30 years of September data.