Mariehamn — Water Temperature in September
Water Temperature Range
11°C
minimum
14°C
average
19°C
maximum
Water Temperature Chart for Month
The chart shows the average daily water temperature for each day of the month based on historical data.
Table of Water Temperatures by Day of the Month for Previous Years
| Day | 2025 | 2024 | 2023 | 2022 |
|---|---|---|---|---|
| SEP 1 | 17°C | 14°C | 15°C | 18°C |
| SEP 2 | 16°C | 14°C | 15°C | 17°C |
| SEP 3 | 16°C | 14°C | 15°C | 18°C |
| SEP 4 | 16°C | 14°C | 15°C | 17°C |
| SEP 5 | 15°C | 14°C | 14°C | 17°C |
| SEP 6 | 15°C | 14°C | 14°C | 17°C |
| SEP 7 | 15°C | 15°C | 14°C | 17°C |
| SEP 8 | 15°C | 15°C | 14°C | 17°C |
| SEP 9 | 15°C | 15°C | 14°C | 17°C |
| SEP 10 | 15°C | 15°C | 14°C | 17°C |
| SEP 11 | 14°C | 14°C | 13°C | 16°C |
| SEP 12 | 14°C | 15°C | 13°C | 15°C |
| SEP 13 | 14°C | 15°C | 13°C | 15°C |
| SEP 14 | 14°C | 14°C | 13°C | 15°C |
| SEP 15 | 15°C | 15°C | 13°C | 15°C |
| SEP 16 | 15°C | 15°C | 13°C | 15°C |
| SEP 17 | 14°C | 15°C | 13°C | 14°C |
| SEP 18 | 14°C | 15°C | 14°C | 14°C |
| SEP 19 | 14°C | 15°C | 13°C | 14°C |
| SEP 20 | 14°C | 15°C | 13°C | 14°C |
| SEP 21 | 14°C | 15°C | 13°C | 13°C |
| SEP 22 | 13°C | 15°C | 12°C | 13°C |
| SEP 23 | 13°C | 15°C | 12°C | 13°C |
| SEP 24 | 13°C | 15°C | 12°C | 13°C |
| SEP 25 | 13°C | 15°C | 12°C | 12°C |
| SEP 26 | 13°C | 14°C | 12°C | 12°C |
| SEP 27 | 12°C | 13°C | 12°C | 13°C |
| SEP 28 | 12°C | 13°C | 12°C | 13°C |
| SEP 29 | 13°C | 13°C | 13°C | 13°C |
| SEP 30 | 12°C | 13°C | 12°C | 13°C |
September: Climate and Swimming Opportunities
Average Night Air Temperature
7°C
Average Day Air Temperature
14°C
Precipitation Amount per Month
59 mm
Number of Rainy Days
11
Daylight per Day
13 hrs
Sunshine per Day
4 hrs
Average Wind Speed
16 km/h
Average Humidity
83%
With such a ratio between the average monthly temperatures of water and air, swimming feels very cold and is only for cold-water enthusiasts. Most people will prefer just a brief splash, because warming up afterward can take time.