Weather in Mariehamn in September 2025
- September is usually the driest month of the year in Mariehamn
Average weather
Average temperature in Mariehamn in September
Going from a maximum of +19°C during the day to a minimum of +12°C during the night, the temperature in September averages around +17°C.
The average maximum temperature goes down 14% by the end of the month, compared with the beginning of the month, from +17°C to +16°C.
Is Mariehamn warm or cold in September?
Mariehamn 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 +14°C to +10°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 Mariehamn:
Climate in Mariehamn in September
| August | September | October | ||||
|---|---|---|---|---|---|---|
| Avg. temperature | ||||||
| +18°C | +14°C | +9°C | ||||
| Min. temperature | ||||||
| +6°C | +1°C | -6°C | ||||
| Max. temperature | ||||||
| +28°C | +24°C | +17°C | ||||
| Rainfall | ||||||
| 63 mm | 55 mm | 64 mm | ||||
| Wind | ||||||
| 5 m/s | 6 m/s | 6 m/s | ||||
| Humidity | ||||||
| 83% | 81% | 81% | ||||
| Air pressure | ||||||
| 1011 HPa | 1012 HPa | 1011 HPa | ||||
| Sunny days | ||||||
| 7 | 4 | 3 | ||||
| Cloudy days | ||||||
| 8 | 10 | 11 | ||||
| Rainy days | ||||||
| 16 | 15 | 17 | ||||
| Snowy days | ||||||
| 0 | 0 | 1 | ||||
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 63 mm to 55 mm. It feels drier, as humidity decreases from 83% to 81%. Winds are stronger in comparison to August, going up from 5 m/s to 6 m/s on average. The days becoming less sunny, going from 7 sunny days in August to 4 in September.
October brings much the same weather, it remains ok.
Wind
The average wind speed is 4 m/s getting up to 7 m/s which is a medium breeze. You can feel it, especially getting out of the water.
The average wind speed in Mariehamn is gradually increasing during September, going from 3 m/s to 4 m/s over the course of the month.
Rain
How was the weather last September in Mariehamn?
Climate Change over Years
The climate in Mariehamn in September has not changed much over the last 43 years.
The average temperature was the lowest in 1987 (+5°C) and the highest in 2020 (+11°C). The driest year was 2018 with only 269 mm of rainfall, and the wettest year was 2020 with 612 mm.
FAQ
Is September a good time to visit Mariehamn?
Can you sunbathe in Mariehamn in September?
Is Mariehamn rainy in September?
Is it sunny in Mariehamn in September?
Monthly weather in Mariehamn
Source of the data
For this page, we’ve looked at the typical weather in Mariehamn, 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.