Click on a day for an hourly weather forecast
The temperatures in Sarnia in September are comfortable with low of 14°C and and high up to 22°C.
You can expect about 3 to 8 days of rain in Sarnia during the month of September. It’s a good idea to bring along your umbrella so that you don’t get caught in poor weather.
Our weather forecast can give you a great sense of what weather to expect in Sarnia in September 2025.
If you’re planning to visit Sarnia in the near future, we highly recommend that you review the 14 day weather forecast for Sarnia before you arrive.
| Month | Temperatures | Rainy Days | Dry Days | Snowy Days | Rainfall | Weather | More details |
|---|---|---|---|---|---|---|---|
| January | -2° / -7° | 11 | 17 | 3 | 22 mm | Awful | Sarnia in January |
| February | -1° / -7° | 8 | 15 | 5 | 23 mm | Awful | Sarnia in February |
| March | 5° / -3° | 7 | 21 | 3 | 27 mm | Awful | Sarnia in March |
| April | 11° / 3° | 8 | 21 | 1 | 39 mm | Ok | Sarnia in April |
| May | 18° / 9° | 7 | 24 | 0 | 36 mm | Good | Sarnia in May |
| June | 23° / 14° | 7 | 23 | 0 | 38 mm | Perfect | Sarnia in June |
| July | 26° / 18° | 7 | 24 | 0 | 30 mm | Perfect | Sarnia in July |
| August | 25° / 17° | 6 | 25 | 0 | 29 mm | Perfect | Sarnia in August |
| September | 22° / 14° | 6 | 24 | 0 | 29 mm | Good | Sarnia in September |
| October | 15° / 8° | 8 | 24 | 0 | 39 mm | Good | Sarnia in October |
| November | 8° / 2° | 8 | 22 | 1 | 26 mm | Ok | Sarnia in November |
| December | 2° / -3° | 9 | 19 | 3 | 24 mm | Awful | Sarnia in December |