The highest day temperature in September 2025 was 71°F. The lowest night temperature was 40°F. The average values for day and night temperatures during September were 61.6°F и 55.2°F respectivly.

The average sea surface temperature in September 2025 for Helsinki was 60.6°F. The maximum and minimum values were 54.4°F and 64.8°F respectively.

You can expect various weather conditions during September. Be ready for sunny, cloudy or even gloomy days.

Precipitation total in September for Helsinki is 1.8 in.

The average wind speed in September is 10.3 mph.

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 Helsinki in September is 6.9 hours.