September in Duluth averages a daily high of 19.7°C with nights around 10.8°C. Expect roughly 8.9 wet days totalling 79.4mm. Comfortable conditions for being outdoors all day.
Across the year, the best time to visit Duluth is June–September.
Based on SUPERIOR, WI US (6.8km), 1995–2024. 27 years of September data.