The official Swedish definition when autumn starts according SMHI, is following:

Autumn
Autumn arrives when autumn temperatures prevail for five consecutive days. Autumn temperatures are when the daily average temperature is below 10.0°C, but not yet for five consecutive days. The arrival date of autumn refers to the first day of five with autumn temperatures. August 1 has been set as the earliest permitted date for the arrival of autumn. The latest possible date for the arrival of autumn is February 14.

Here we see how much Sweden was covered by Autumn on a 27 Aug during the past 3 years. It also confirms that this August has been cooler than other previous years, as autumn each year has been conquering larger parts of Sweden when comparing 27 Aug 2025 with 2023 and 2024.