Finland
Helsinki in September: weather, sea & travel advice
This month's data profile
Rain shapes the decision
Helsinki in September is climatically mixed. The average daily high is around 15 °C, and the sea is about 15 °C. With about 12 rainy days it is wet.
Historical monthly averages, not a weather forecast. Individual days and years can differ substantially.
Rank among 12 monthly averages
40/100 · #5
Warmth
#4
Dryness
#7
Sun
#6
Sea warmth
#3
Published best categories: City break
Helsinki · SeptemberPhoto: Matti Mattila · CC BY 2.0Climate facts
- Average high
- 15 °C
- Average low
- 11 °C
- Sea
- 15 °C
- Rainy days (est.)
- 12 rainy days (est.)
- Sun (est.)
- 3 h/day
- Humidity
- 83 %
Climate evidence with direct month comparison
The highlighted row is the selected month. Precipitation total and rainy days are separate monthly averages.
| Month | Avg high °C | Avg low °C | Rainy days (est.) | Precipitation mm | Sun h/day (est.) | Humidity % | Wind m/s | Sea °C | Score |
|---|---|---|---|---|---|---|---|---|---|
| August | 19 | 15 | 13 | 73 | 5.1 | 81 | 3.1 | 17 | 55 |
| September (selected) | 15 | 11 | 12 | 63 | 3.1 | 83 | 3.8 | 15 | 40 |
| October | 9 | 6 | 14 | 82 | 1.3 | 86 | 4.3 | 10 | 21 |
How do the previous and next months compare?
Baseline: September (40/100)
Positive and negative values show the change from the selected month.
| Score Δ | Average high Δ | Average low Δ | Rainy days Δ | Rain Δ | Sun Δ | Humidity Δ | Wind Δ | Sea Δ | |
|---|---|---|---|---|---|---|---|---|---|
| August | +15 | +4.2 °C | +3.7 °C | +1.3 | +10 mm | +2 h | -2 % | -0.6 m/s | +2.6 °C |
| October | -19 | -5.9 °C | -5.3 °C | +2.7 | +19.6 mm | -1.8 h | +3.7 % | +0.5 m/s | -4.2 °C |
All twelve months in context
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Useful next decisions
Frequently asked questions
How warm is Helsinki in September?
The average daily high is around 15 °C, with an average daily low of about 11 °C.
Can you swim in Helsinki in September?
The sea is about 15 °C (cold).
Does it rain a lot in Helsinki in September?
The curated estimate is about 12 rainy days per month, not a directly measured long-term average. Total precipitation averages around 63 mm for the month. A rainy day does not mean all-day rain.
When is the best time to visit Helsinki?
By the climate score, July are the strongest months for Helsinki. September is not among them.