Autumn is coming, why is it suddenly getting cold?

Astronomically speaking, June 22nd is the summer solstice. At this time, the sun shines on the tropic of cancer, and the sunshine time is the longest, that is, the hottest time. After June 22, the sun gradually moved south and the weather gradually cooled down. However, until September 23, the sun was still shining in the northern hemisphere, so it was still hot during this time, but it was gradually cooling down.

There is an old saying called "a burst of autumn rain and a burst of cold", which refers to this gradual cooling situation.

Recently, the cooler weather is caused by the weakening of subtropical high, El Nino phenomenon and frequent Pacific airflow activities, but it is not typical weather.