September in Longueuil averages a daily high of 21.5°C with nights around 12.7°C. Expect roughly 9.9 wet days totalling 87.9mm. Comfortable conditions for being outdoors all day.
Across the year, the best time to visit Longueuil is May–September.
Based on MCTAVISH, QC CA (9.1km), 1995–2024. 27 years of September data.