September in Sundsvall averages a daily high of 14.8°C with nights around 6.1°C. Expect roughly 11.8 wet days totalling 65.5mm. Generally workable, with some weather to plan around.
Across the year, the best time to visit Sundsvall is June–August.
Based on SIDSJO, SW (1.5km), 1995–2024. 11 years of September data.