September in Słupsk averages a daily high of 18.3°C with nights around 10.1°C. Expect roughly 13.3 wet days totalling 74.1mm. Generally workable, with some weather to plan around.
Across the year, the best time to visit Słupsk is June–August.
Based on LEBA, PL (45.5km), 1995–2024. 30 years of September data.