September in Castelldefels averages a daily high of 26.3°C with nights around 18.4°C. Expect roughly 7.1 wet days totalling 74.3mm. Comfortable conditions for being outdoors all day.
Across the year, the best time to visit Castelldefels is May–July.
Based on BARCELONA AEROPUERTO, SP (8.5km), 1995–2024. 30 years of September data.