September weather forecast
Mariehamn Airport, Finland

September in Mariehamn Airport signifies the advent of autumn with a noticeable dip in temperature, rainier days and diminishing daylight hours from August. Another characteristic feature of September is the gradual decline in sunshine hours. Although the rainfall continues in abundance, the sea temperature drops, indicating a change in maritime climate. Meanwhile, the UV index starts to lower, indicating lesser intensity, and impact, of sunlight.

Temperature

September in Mariehamn Airport signifies a minor drop in average high-temperature, transitioning from a comfortable 18°C (64.4°F) in August to a mild 14°C (57.2°F). During September, Mariehamn Airport records an average temperature of 7°C (44.6°F) at night.

Rainfall

In Mariehamn Airport, Finland, in September, it is raining for 16 days, with typically 61mm (2.4") of accumulated precipitation. Throughout the year, in Mariehamn Airport, Finland, there are 176 rainfall days, and 508mm (20") of precipitation is accumulated.

Sea temperature

In Mariehamn Airport, in September, the average water temperature is 13°C (55.4°F).
Note: With the appropriate swimsuit, one can swim in 13°C (55.4°F) even if temperatures dip below 10°C (50°F); otherwise, be ready for cold shock and breath issues. A fleeting swim around 13°C (55.4°F) is distressing.

Daylight

In September, the average length of the day is 12h and 52min.
On the first day of the month, sunrise is at 06:36 and sunset at 20:44. On the last day of September, in Mariehamn Airport, sunrise is at 07:44 and sunset at 19:15 EEST.

Sunshine

In Mariehamn Airport, the average sunshine in September is 4h.

UV index

In September, the average daily maximum UV index in Mariehamn Airport is 3. A UV Index of 3 to 5 symbolizes a moderate health risk from exposure to the Sun's UV radiation for the ordinary person.
Note: The average daily UV index of 3 in September transforms into the following instructions:
Guard yourself - Precautionary measures against sun damage are advocated. The most potent solar radiation is around mid-day, so one should minimize exposure to direct sunlight during this period. A wide-brim hat offers excellent sun protection for the eyes, ears, face, and neck. Sunglasses with UVA and UVB protection significantly reduce eye damage from sun exposure.