Weather in Trondheim in September 2025
Average weather
Average temperature in Trondheim in September
The temperature in September is +16°C on average, with a range between a maximum of +23°C during the day and a minimum of +3°C at night.
The average maximum temperature goes down 20% by the end of the month, compared with the beginning of the month, from +17°C to +13°C.
Is Trondheim warm or cold in September?
Trondheim is typically mild in September.
Maximum temperatures go down compared to the previous month from +18°C to +14°C. The minimum temperature also goes down from +10°C to +7°C.
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 Trondheim:
Water temperature in Trondheim in September
Water in Trondheim in September is Cold. It varies from +11°C to +15°C, with an average of +13°C. This is almost similar to the air temperature, which averages +14°C.
The water temperature in September is one of the warmest of the entire year:
Can you swim in Trondheim in September?
Climate in Trondheim in September
| August | September | October | ||||
|---|---|---|---|---|---|---|
| Avg. temperature | ||||||
| +18°C | +14°C | +9°C | ||||
| Min. temperature | ||||||
| +2°C | -2°C | -12°C | ||||
| Max. temperature | ||||||
| +30°C | +25°C | +22°C | ||||
| Rainfall | ||||||
| 124 mm | 121 mm | 92 mm | ||||
| Wind | ||||||
| 1 m/s | 1 m/s | 2 m/s | ||||
| Avg. water temperature | ||||||
| +15°C | +13°C | +11°C | ||||
| Humidity | ||||||
| 78% | 79% | 80% | ||||
| Air pressure | ||||||
| 1010 HPa | 1010 HPa | 1008 HPa | ||||
| Sunny days | ||||||
| 1 | 2 | 2 | ||||
| Cloudy days | ||||||
| 7 | 7 | 8 | ||||
| Rainy days | ||||||
| 23 | 21 | 18 | ||||
| Snowy days | ||||||
| 0 | 0 | 3 | ||||
September weather is still as ok as in August. It’s getting colder in September. From +18°C in the day, the average maximum temperature lowers to +14°C. As September arrives, the amount of rainfall goes down. On average, the rainfall volume decreases from 124 mm to 121 mm. Humidity rises from 78% to 79%. The average wind speed doesn’t change much during September, staying around 1 m/s. The good news is there are likely to be more sunny days in September, from 1 to 2.
October brings much the same weather, it remains ok.
Wind
The average wind speed is 1 m/s getting up to 2 m/s which is a light breeze; barely moving the tree leaves.
The average wind speed in Trondheim is gradually increasing during September, going from 0 m/s to 0 m/s over the course of the month.
Rain
How was the weather last September in Trondheim?
Climate Change over Years
The climate in Trondheim in September has not changed much over the last 43 years.
The average temperature was the lowest in 1981 (+7°C) and the highest in 2014 (+11°C). The driest year was 2002 with only 617 mm of rainfall, and the wettest year was 2007 with 1311 mm.
FAQ
Is September a good time to visit Trondheim?
Can you sunbathe in Trondheim in September?
Can you swim in Trondheim in September?
Is Trondheim rainy in September?
Is it sunny in Trondheim in September?
Other cities in Norway
Monthly weather in Trondheim
Source of the data
For this page, we’ve looked at the typical weather in Trondheim, 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.