The highest day temperature in September 2025 was 70°F. The lowest night temperature was 44°F. The average values for day and night temperatures during September were 59.9°F и 52.2°F respectivly.

The average sea surface temperature in September 2025 for Trondheim was 56.7°F. The maximum and minimum values were 52.6°F and 60.4°F respectively.

Most of the days in September are gloomy but you can also expect sunny days.

Precipitation total in September for Trondheim is 3.0 in. It makes september one of the most rainy months of the year.

The average wind speed in September is 6.5 mph. This value is relatively stable throughout the year.

We are using day length and cloud cover information for each day of the month to calculate averages for this chart. Average sunny hours for Trondheim in September is 6.2 hours.