Last month was exceptionally warm in Finland, the institute said on Thursday, noting that the southeastern towns of Heinola and Tohmajärvi surpassed their previous heat records for August.
The southwestern town of Pori recorded the month's highest temperature—31.7 degrees Celsius—on 16 August, while Ylivieska in North Ostrobothnia saw the period's lowest reading of -2.9C on 31 August.
Average temperatures in August ranged from around 19C in southern coastal areas to 12C in northwestern Finnish Lapland.
There were a total of 19 "heatwave" days in Finland in August, when the temperature exceeded 25 degrees Celsius. The last time August saw more 25-degree-Celsius weather was in 2006, when meteorologists recorded 27 such days.
In Helsinki, this was the fifth hottest summer on record, FMI researcher Mika Rantanen noted in a tweet, adding that eight of the top 10 hottest summers have been since 1997.
Finland also saw an exceptional amount of sunshine last month, while lightning also struck the country more often than usual, according to the FMI.