September Weather in Helsinki, Finland

Last updated: August 21, 2025

September in Helsinki, Finland offers a dynamic weather experience, with temperatures ranging from a brisk -1°C (31°F) at night to a pleasant 23°C (73°F) during the day, averaging around 12°C (54°F). As autumn sets in, the city experiences 76 mm (3.0 in) of rainfall over 13 days, contributing to a high humidity level of 90%. This month serves as a beautiful transition, where the vibrant hues of early fall contrast with the lingering warmth of summer, inviting residents and visitors alike to embrace the season's charm.

September Temperature in Helsinki

As September unfolds in Helsinki, a noticeable shift in temperatures signals the transition from summer to fall. The month starts with a minimum temperature nearing -1°C (31°F), gradually warming to an average of 12°C (54°F), and reaching a pleasant maximum of 23°C (73°F). This change heralds cooler days, yet allows for the lingering warmth of late summer, making it an ideal time for outdoor exploration in the city's vibrant parks and waterfronts. As the days shorten and the air turns crisp, Helsinki's charm becomes even more pronounced, inviting residents and visitors alike to savor the beauty of autumn amidst a backdrop of softening hues in nature.

September Weather in Helsinki: Daily Temperature Highs, Lows, and Averages

The chart illustrates September temperature patterns in Helsinki, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Helsinki, September typically has an average temperature of {2}°C ({3}°F), with highs reaching up to {4}°C ({5}°F) and lows dropping to around {6}°C ({7}°F).
JanFebMarAprMayJunJulAugSepOctNovDec272630395061646254453830
Data source: Temperature data for Helsinki generated using information from the Copernicus Climate Change Service.
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The average of daily temperatures (24 hours) calculated across all days in the month.

September Precipitation in Helsinki

September in Helsinki brings about a transitional shift in weather, with precipitation reaching 76 mm (3.0 in) over the month, accompanied by 13 days of rain. This marks a subtle uptick from the drier summer months of July and August, which saw higher totals but fewer days of rainfall. As autumn approaches, the wet conditions become more pronounced, setting the stage for the wetter October that typically follows. This pattern highlights Helsinki’s climate variability, as the city prepares to welcome the cooler, more saturated months ahead. The balance between precipitation amount and rainy days suggests a notable trend—September serves as a bridge from the moisture-rich summer into the more consistent rain of fall.

September Precipitation Trends in Helsinki

The chart displays monthly precipitation patterns in Helsinki, with values for each month alongside September’s data, which is highlighted for easy comparison. It shows the amount of precipitation, providing insights into how September’s conditions compare to those of other months. In Helsinki, September typically receives around {2} mm ({3} inches) of precipitation spread over approximately {4} days.
JanFebMarAprMayJunJulAugSepOctNovDec554852485661918376896273
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Helsinki

In September, Helsinki experiences a notable increase in humidity, reaching 90% as the city transitions into the autumn months. This uptick follows the relatively stable levels seen in the summer months, where humidity fluctuated around 75% to 83%. As the warmth of August gives way to cooler temperatures, the humidity tends to rise again, echoing patterns from earlier months in the year. Interestingly, while the humidity peaks in January at 97%, September's levels indicate a consistent trend of increased moisture in the air as seasons shift, setting the stage for the wetter fall and winter months that follow.

September Average Humidity in Helsinki

This chart illustrates the average monthly humidity levels in Helsinki, with September’s data highlighted for easy comparison. It shows the fluctuation in humidity throughout the year, helping you understand how conditions vary by season. In September, average humidity in Helsinki is approximately {2}%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec97%95%93%87%75%75%80%83%90%93%94%95%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Helsinki

As September arrives in Helsinki, the UV Index reflects a gradual decline, settling at 4, which falls within the moderate exposure category. This signals a shift from the high levels experienced during the peak summer months of June and July, where the Index registered a more intense 7. With a burn time of just 30 minutes, it's essential to remain vigilant about sun protection, particularly during midday hours. This month’s moderate UV Index serves as a reminder that while the sunny days of summer are fading, the sun still holds enough strength to warrant caution. As the seasons transition, staying informed about sun exposure is vital for maintaining healthy skin. For more details, check out the comprehensive guide to the Helsinki UV Index.

Maximum UV Index Levels in Helsinki for September

The chart shows the monthly maximum UV Index (UVI) for Helsinki in September, representing the highest UV radiation level. The UVI measures the intensity of ultraviolet radiation from the sun, indicating the potential risk of sunburn and UV-related health issues. In September, the maximum UV index in Helsinki typically reaches {2}, which falls under the {3} exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec113457754211
Data source: Helsinki September UVI data generated using information from the Copernicus Climate Change Service.

UV Risk Categories

  •  Extreme (11+): Avoid the sun, stay in shade.
  •  Very High (8-10): Limit sun exposure.
  •  High (6-7): Use SPF 30+ and protective clothing.
  •  Moderate (3-5): Midday shade recommended.
  •  Low (0-2): No protection needed.

September Sunshine in Helsinki

As summer gently transitions into autumn, September in Helsinki continues to bask in warm sunlight, boasting an impressive 290 hours of sunshine. This month marks a delightful decline from the peak of 493 hours in June, signaling the gradual cool down as days shorten. Compared to earlier months, however, September still enjoys significantly more sunshine than the winter months, with stark contrasts to the chilly January and February, which see a mere 55 and 154 hours, respectively. Although the light begins to wane in October, September offers a beautiful blend of lingering warmth and vibrant autumn colors, making it a perfect time to savor the last rays of summer before the chilly embrace of winter.

Monthly Sunshine Duration in Helsinki: September Highlighted

The September sunshine duration represents the total number of hours Helsinki experiences direct sunlight during the month of September, excluding cloudy or obstructed periods. This chart compares the sunshine duration of September with the other months of the year.
JanFebMarAprMayJunJulAugSepOctNovDec55h154h261h362h451h493h485h406h290h190h113h58h
Data source: Helsinki September Sunshine duration data generated using information from the Copernicus Climate Change Service.

Chance of Sun in Helsinki During September

In September, Helsinki experiences a noticeable decline in sunny weather, with the likelihood of sunshine dropping to 28%. This trend follows a summer peak in July, where the sun shines most brightly at 56%. As the months transition from the vibrant sun-filled days of summer to the cooler, cloudier autumn, September marks a turning point. Although the chances of sunny skies are significantly lower than in the preceding months, they still offer a glimpse of warmth amidst the encroaching chill, making it a transitional month where the last remnants of summer subtly yield to the impending autumn.

Percentage of Sunny Days in September in Helsinki

The chart illustrates the percentage of sunny days in Helsinki throughout the year, with September highlighted. It highlights the variation in sunshine across each month and provides an overview of the typical frequency of sunny days, offering insights into how often Helsinki experiences clear skies throughout the year.
JanFebMarAprMayJunJulAugSepOctNovDec5%15%38%44%31%53%56%29%28%19%19%14%
Data source: Helsinki September chance of sun data, generated using information from the Copernicus Climate Change Service.

Daylight Hours in Helsinki in September

As September unfolds in Helsinki, Finland, daylight begins its steady decline after the peak summer months. With an average of 12 hours of daylight, the city experiences a noticeable shift from the long, sunlit days of June and July. This transition reflects the gradual onset of autumn, where the days shrink from the 17 hours in July to 15 in August and now to 12. As leaves begin to change and the air turns crisper, residents and visitors alike can appreciate the lingering warmth of the sun while they still can, before it drops to 10 hours in October and even further into the darker winter months. This ebb and flow of daylight underscore the captivating seasonal transformations that define life in this Nordic metropolis.

Average Daylight Hours in Helsinki for September

The chart illustrates the variation in daylight duration in Helsinki throughout the year, with September highlighted. It shows the monthly changes in daylight hours, calculated by summing the hours between sunrise and sunset.
JanFebMarAprMayJunJulAugSepOctNovDec6h 45m9h 7m11h 51m14h 38m17h 14m18h 45m17h 56m15h 31m12h 48m10h 2m7h 27m5h 56m
Data source: Helsinki daylight hours, calculated by summing the hours between sunrise and sunset for each day.

September Winds in Helsinki

As the summer fades, September in Helsinki brings a gentle increase in wind—averaging 4.1 m/s (9 mph)—that marks a subtle transition into fall. This month stands out as a bridge between the lighter breezes of summer, which dip to around 3.0 m/s in June, and the sharper gusts that characterize October, where average wind speeds reach 5.2 m/s (12 mph). Notably, September's winds are slightly up from July and August, reflecting a shift toward the more dynamic weather patterns typical of autumn. This gradual intensification not only enhances the vibrant hues of the city’s foliage but also invites the locals and visitors alike to embrace the invigorating embrace of the crisp, changing season.

Average September Wind Speed in Helsinki

The chart displays monthly wind speed patterns in Helsinki, with values for each month shown alongside September's data, which is highlighted for easy comparison. It illustrates the average wind speed, offering insights into how September's wind conditions compare to the rest of the year.
JanFebMarAprMayJunJulAugSepOctNovDec4.03.54.54.13.73.03.54.44.1 m/s5.24.44.2
Data source: Helsinki September wind data, generated using information from the Copernicus Climate Change Service.

How September Weather in Helsinki Compares to Other Months

Weather in Helsinki varies notably across the year, with each month offering distinct climate conditions. This page compares September’s weather to other months in Helsinki, focusing on differences in temperature, rainfall, humidity, and UV levels.

September and January present starkly contrasting weather conditions. In September, temperatures range from a chilly -1°C (31°F) at the lowest to a pleasant 23°C (73°F) at their peak, with an average of 12°C (54°F). The month experiences moderate precipitation, totaling 76 mm (3.0 in) over 13 days, and humidity levels hover around 90%. In contrast, January is much colder, with temperatures plunging to a minimum of -23°C (-9°F) and only reaching a maximum of 8°C (46°F), averaging -3°C (28°F). Precipitation is lighter at 55 mm (2.2 in) across 11 days, but humidity is higher at 97%, contributing to a notably brisk and frigid atmosphere. For more details, visit Helsinki weather in January.

September and February present stark contrasts in weather. In September, temperatures range from a chilly 1°C (34°F) at night to a comfortable 23°C (73°F) during the day, with an average of 12°C (54°F). The month sees around 76 mm (3.0 in) of precipitation over 13 days and is characterized by a humidity level of 90%. In contrast, February is much colder, with temperatures dipping as low as -23°C (-8°F) and only peaking at 6°C (43°F), averaging -3°C (26°F). Notably, February receives less precipitation at 48 mm (1.9 in) over 10 days but has a higher humidity level of 95%. For more specific information about the weather in February, you can visit Helsinki weather in February.

September and March showcase contrasting weather patterns. In September, temperatures range from a minimum of -1°C (31°F) to a comfortable maximum of 23°C (73°F), with an average of 12°C (54°F). The month experiences 76 mm of precipitation over 13 days and humidity levels around 90%. In contrast, March is much chillier, with minimum temperatures plummeting to -22°C (-7°F) and a maximum of only 10°C (51°F), averaging at -1°C (31°F). While precipitation is slightly lower at 52 mm over 12 days, humidity remains high at 93%. For more details on March weather, you can visit Helsinki weather in March.

When comparing the weather in September and April, notable differences emerge. September tends to be milder with average temperatures around 12°C (54°F) and a maximum of 23°C (73°F), whereas April is generally cooler, with an average of only 4°C (39°F) and a maximum of 19°C (67°F). Precipitation is more frequent in September, occurring over 13 days and totaling 76 mm (3.0 in), compared to April, which experiences 9 days of rain and 48 mm (1.9 in). Additionally, humidity levels are slightly higher in September at 90%, compared to 86% in April. For more detailed insights, you can check Helsinki weather in April.

When comparing the weather in September and May, we see contrasting conditions that reflect the transition between seasons. September tends to be milder, with average temperatures around 12°C (54°F) and a maximum of 23°C (73°F), while May has a slightly cooler average of 10°C (50°F) and can reach up to 27°C (80°F). Precipitation is more frequent in September, with about 76 mm (3.0 in) falling over 13 days compared to 56 mm (2.2 in) over 10 days in May. Additionally, September experiences higher humidity at 90%, compared to May's more comfortable 75%. For a closer look at what to expect, you can check Helsinki weather in May.

In comparing the weather of September and June, we see notable differences in temperature and humidity. September experiences cooler temperatures, with a minimum of -1°C (31°F) and an average of 12°C (54°F), while June boasts warmer temperatures, ranging from a minimum of 3°C (38°F) and averaging 16°C (62°F) up to a high of 30°C (86°F). Additionally, September is characterized by higher humidity at 90%, compared to June's 75%. Precipitation is also slightly higher in September, with 76 mm (3.0 in) over 13 days, versus June's 61 mm (2.4 in) over 10 days. For more details, you can explore Helsinki weather in June.

Comparing the weather in September and July reveals notable differences in temperature and humidity. September experiences cooler temperatures with a minimum of -1°C (31°F) and an average of 12°C (54°F), whereas July sees milder conditions with a minimum of 8°C (46°F) and an average of 18°C (65°F). Additionally, July can reach maximum temperatures of up to 32°C (90°F), significantly warmer than September’s highest of 23°C (73°F). Precipitation levels are relatively similar, with July recording 91 mm (3.6 in) and September slightly lower at 76 mm (3.0 in), both spread over 13 days. However, September has a higher humidity level at 90% compared to July's 80%. For a more detailed look at the July weather, you can visit Helsinki weather in July.

Comparing the weather conditions in September and August reveals notable differences. September tends to be cooler, with minimum temperatures dropping to -1°C (31°F) and an average of 12°C (54°F), whereas August enjoys milder temperatures that range from a minimum of 7°C (45°F) to an average of 17°C (62°F) and can peak at 29°C (84°F). In terms of precipitation, September sees a slight decrease in total rainfall (76 mm or 3.0 in) compared to August (83 mm or 3.3 in), although both months experience precipitation on 13 days. Humidity levels are higher in September at 90%, compared to August's 83%. For more detailed insights, you can check Helsinki weather in August.

September's weather is characterized by milder temperatures, with average highs reaching 23°C (73°F) and lows around 1°C (34°F). The month experiences moderate precipitation, totaling 76 mm (3.0 in) over about 13 days, with 90% humidity providing a relatively comfortable, if damp, climate.

In contrast, October brings a noticeable drop in temperatures, with average highs only reaching 16°C (62°F) and lows dipping to -4°C (25°F). Precipitation increases slightly to 89 mm (3.5 in) over 17 days, and humidity edges up to 93%, contributing to a chillier and more persistent wetness. For more detailed information, you can check Helsinki weather in October.

In comparing the weather between September and November, we see a notable shift in temperatures and conditions. September enjoys a milder climate, with average temperatures ranging from -1°C (31°F) at night to a comfortable 23°C (73°F) during the day. In contrast, November experiences colder temperatures, with average highs of only 12°C (54°F) and lows dipping to -7°C (19°F).

Precipitation levels are relatively similar, with September receiving 76 mm (3.0 in) of rain over 13 days, while November totals 62 mm (2.5 in) over the same number of days. Additionally, humidity rises slightly in November to 94% compared to September's 90%, adding to the chill in the air. For more detailed insights, you can explore Helsinki weather in November.

In September, the weather in Helsinki is generally milder, with average temperatures around 12°C (54°F) and maximums reaching 23°C (73°F). Rainfall is moderate at 76 mm (3.0 in) over approximately 13 days, while the high humidity levels of 90% add to the autumn chill. In contrast, December brings much colder conditions, with average temperatures dropping to -1°C (31°F) and maximums only reaching 7°C (44°F). Although precipitation is slightly lower at 73 mm (2.9 in) over about 15 days, the humidity rises to 95%, creating a crisp and chilly atmosphere. For more details on winter conditions, check out Helsinki weather in December.

Compare Helsinki's Climate with Cities Worldwide

Conclusion: What to Expect From September Weather in Helsinki

September in Helsinki marks a transition into autumn, characterized by a notable dip in temperatures compared to the warmer summer months. With an average temperature of 12°C (54°F), it’s a time when the days start to feel brighter yet cooler, and there’s a marked increase in humidity and precipitation. The city experiences around 13 days of rain, contributing to the lush, vibrant landscapes typical of this season. As the warmth of summer fades, visitors can expect a refreshing change, making it an ideal time for exploring the beautiful surroundings. For more insights and detailed information on weather patterns, visit Helsinki Climate.