Japan is a country that takes great delight in the changing of the seasons. It may be the only country in the world where the first day of spring and the first day of fall are national holidays.
October 1 is another important, seasonal day.
Rain or shine, hot or cold, October 1 is Koromo-gae no Hi. This is the day when all uniforms change from the summer version to the winter version, when short sleeves yield to long sleeves, when sandals suddenly disappear and boots are allowed out of the closet.
The weather itself has nothing to do with it. It's October 1. It's time to put on the winter wardrobe.