September in Ajax averages a daily high of 21.3°C with nights around 12.3°C. Expect roughly 9.9 wet days totalling 86.8mm. Comfortable conditions for being outdoors all day.
Across the year, the best time to visit Ajax is June–September.
Based on OSHAWA WPCP, ON CA (16.1km), 1995–2024. 24 years of September data.