September 2023 was the warmest on record, according to the Finnish Meteorological Institute (FMI).
The national average temperature for September was 12.2 degrees Celsius. This was 0.4 degrees higher than the previous record set in 1934.
In Helsinki, the average temperature in September was 15.8 degrees Celsius, about 0.9 degrees above the 1934 record.
Finland officially started tracking weather at the beginning of the 20th century. However some weather stations, like the 180-year-old facility in Kaisaniemi, came into use before that.
Nationally, last month's average temperatures ranged from around 16 degrees on the southern coast to just below eight degrees in northwestern Lapland.
Last month September was also roughly 2-3 degrees warmer than averages seen during 1991 to 2020.
Daily high record not broken
However, September's daily record remained unbroken. That month's all-time daily record of 26.2 degrees was set in 1968.
Last month's highest temperature across the country, 24.1 degrees Celsius, was recorded in Kouvola, on Tuesday the 12th. Meanwhile highest temperature in Helsinki was reached on 8 September, when it hit 20.9 degrees.
The relatively high temperatures were due to a long period of south-westerly air flow, said Jani Sorsa, a meteorologist at the FMI.
"Warm air has been flowing here for much of the month. Usually in September, cooler air from the north blows in, but this time it only reached the northern parts of the country for a few days."
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