Weather in Ottawa in September 2025
Average weather
Average temperature in Ottawa in September
Going from a maximum of +91°F during the day to a minimum of +45°F during the night, the temperature in September averages around +73°F.
The average maximum temperature goes up 4% by the end of the month, compared with the beginning of the month, from +75°F to +77°F.
Is Ottawa warm or cold in September?
Ottawa is typically mild in September.
Maximum temperatures go down compared to the previous month from +77°F to +70°F. The minimum temperature also goes down from +59°F to +52°F.
Pack a light jacket as it will be warm in the day and cool in the evenings.
Take a look at how September is compared to other months in Ottawa:
Climate in Ottawa in September
| August | September | October | ||||
|---|---|---|---|---|---|---|
| Avg. temperature | ||||||
| +77°F | +70°F | +55°F | ||||
| Min. temperature | ||||||
| +39°F | +27°F | +18°F | ||||
| Max. temperature | ||||||
| +97°F | +95°F | +86°F | ||||
| Rainfall | ||||||
| 85 mm | 88 mm | 90 mm | ||||
| Wind | ||||||
| 2 m/s | 2 m/s | 3 m/s | ||||
| Humidity | ||||||
| 72% | 75% | 76% | ||||
| Air pressure | ||||||
| 1014 HPa | 1016 HPa | 1015 HPa | ||||
| Sunny days | ||||||
| 4 | 4 | 3 | ||||
| Cloudy days | ||||||
| 11 | 12 | 12 | ||||
| Rainy days | ||||||
| 12 | 12 | 14 | ||||
| Snowy days | ||||||
| 0 | 0 | 1 | ||||
September typically has worse weather conditions compared to August. It’s getting colder in September. From +77°F in the day, the average maximum temperature lowers to +70°F. Prepare for more rain. Average rainfall goes from 85 mm to 88 mm. Humidity rises from 72% to 75%. The average wind speed doesn’t change much during September, staying around 2 m/s. The amount of sunny days stay about the same, averaging 4 sunny days during the month.
October brings much the same weather, it remains ok.
Wind
The average wind speed is 3 m/s getting up to 5 m/s which is a light breeze; barely moving the tree leaves.
The average wind speed in Ottawa is gradually increasing during September, going from 2 m/s to 2 m/s over the course of the month.
Rain
How was the weather last September in Ottawa?
Climate Change Over the Years
The climate in Ottawa in September has not changed that much over the last 43 years.
The average temperature was the lowest in 1992 (+51°F) and the highest in 2012 (+56°F). The driest year was 1985 with only 469 mm of rainfall, and the wettest year was 2017 with 1378 mm.
FAQ
Is September a good time to visit Ottawa?
Can you sunbathe in Ottawa in September?
Is Ottawa rainy in September?
Is it sunny in Ottawa in September?
Other cities in Canada
Monthly weather in Ottawa
Source of the data
For this page, we’ve looked at the typical weather in Ottawa, based on historical hourly weather data from January 1, 1979, to December 31, 2023.
For past dates, we show actual recorded data at the location at that time. Forecasts are based on recorded weather during that day of the year, averaged over the total years for which we have records (unless stated otherwise). The daily temperature is the highest recorded temperature in the shadow during that day.