August in Sarnia averages a daily high of 26.8°C with nights around 17.6°C. Expect roughly 10.2 wet days totalling 82.2mm. Comfortable conditions for being outdoors all day.
Across the year, the best time to visit Sarnia is May–September.
Based on PORT HURON, MI US (1.3km), 1995–2024. 30 years of August data.