Weather in mid September?

Beijing and Xian in mid September would be cool and mild with pleasant sunshine. The average temperature is about 20 C. Long-sleeved and light coat are needed to prepared. In Xian, during that time, it may rain a lot, sometimes with heavy rain.
For Yangtze River, it could be humid and a little hot. About 25 C average temperature make fall on the tourists at that time.
Shanghai would be hot then with the average temeprature of 28 C. So short-sleeved shirt, shorts and dress are needed.