Do you have any friends in Yunnan? What's the actual weather there now? What clothes should I take to go in early September?

You want to go there to play, Yunnan is too large, so I'll give you a reference:

Kunming, Yunnan —— It maintains a comfortable living temperature for human beings all the year round, but it will still be slightly cold in September, but it will never be so cold that you need to wear a big down jacket, coat and sweater to be safe (it is almost the same rhythm in the area around Kunming, Yunnan 100 km, and it is windy in the north of Yuxi, Yunnan, but it is still refreshing compared with the northwest).

Pu 'er, Yunnan-This area is a bit hot, typical of Xishuangbanna. If you want to go, you should take some light clothes, so it won't be cold when it rains. The temperature is very stable (generally speaking, but there are exceptions). Going to southern Yunnan in September will not be too hot and there will be less rain. Don't worry too much about mudslides. Pay attention to mosquito prevention, and don't wear too little when you go out at night, or you will feed mosquitoes.

That's about it. Personal views are for reference only. If there are any mistakes, please modify them. After staying in Yunnan for so many years, I feel that the climate is quite good.