Ontario weather in September
September is one of the best months to visit Ontario: highs of 21°C (70°F) and about 66 mm (2.6 in) of rain on average. Nights average 15°C (60°F) and cloud cover 60% (NASA POWER, 2001–2025 averages). It is the 6th wettest month of the year and the 3rd warmest. Compared with August, it is cooler and about as wet; October brings highs of 14°C (57°F) and 74 mm (2.9 in) of rain.
Figures are long-term averages for Toronto, the largest city in Ontario. See below for other places.
Is September a good time to visit Ontario?
best month Weather score 77/100.
Yes. September is one of the best months for weather in Ontario.
Does it rain a lot in Ontario in September?
Some rain is normal: about 66 mm (2.6 in) falls in an average September. It is the 6th wettest month of the year.
How warm is Ontario in September?
Days average 21°C (70°F) and nights 15°C (60°F).
Ontario weather by month
| Month | High | Low | Rain | Cloud | Weather |
|---|---|---|---|---|---|
| January | 0°C (31°F) | -5°C (23°F) | 54 mm | 81% | least pleasant |
| February | 0°C (32°F) | -5°C (22°F) | 49 mm | 79% | least pleasant |
| March | 4°C (38°F) | -2°C (28°F) | 53 mm | 74% | least pleasant |
| April | 9°C (48°F) | 2°C (36°F) | 71 mm | 75% | least pleasant |
| May | 15°C (59°F) | 8°C (46°F) | 73 mm | 74% | fair |
| June | 21°C (70°F) | 14°C (58°F) | 71 mm | 68% | best |
| July | 25°C (77°F) | 18°C (65°F) | 75 mm | 64% | best |
| August | 25°C (76°F) | 19°C (65°F) | 59 mm | 62% | best |
| September | 21°C (70°F) | 15°C (60°F) | 66 mm | 60% | best |
| October | 14°C (57°F) | 9°C (48°F) | 74 mm | 74% | fair |
| November | 8°C (46°F) | 3°C (37°F) | 66 mm | 75% | least pleasant |
| December | 3°C (37°F) | -2°C (29°F) | 63 mm | 81% | least pleasant |
Sources: 2001–2025 monthly averages from NASA POWER (MERRA-2 reanalysis). Page updated . How we rate months
Weather across Ontario in September
Weather can differ a lot within Ontario: coasts, hills and mountains each have their own climate.
| Place | High | Low | Rain | Weather |
|---|---|---|---|---|
| Toronto | 21°C (70°F) | 15°C (60°F) | 66 mm | best |
| Ottawa | 21°C (71°F) | 10°C (50°F) | 87 mm | best |
| Mississauga | 21°C (70°F) | 15°C (60°F) | 66 mm | best |
| Brampton | 23°C (74°F) | 11°C (53°F) | 70 mm | best |
| Hamilton | 23°C (74°F) | 11°C (53°F) | 70 mm | best |
| London | 24°C (74°F) | 12°C (54°F) | 69 mm | best |
| Etobicoke | 21°C (70°F) | 15°C (60°F) | 66 mm | best |
| Markham | 23°C (73°F) | 12°C (54°F) | 59 mm | best |
| Vaughan | 23°C (73°F) | 12°C (54°F) | 59 mm | best |
| Kitchener | 23°C (73°F) | 11°C (51°F) | 70 mm | best |
| Windsor | 23°C (74°F) | 13°C (55°F) | 74 mm | best |
| Oakville | 21°C (70°F) | 15°C (60°F) | 66 mm | best |