What is the September weather and usual climate in Beijing, Shanghai, Xian and Yunnan?

It is the end of summer in September in China. The climate get cooler and cooler from south to north in this order: Yunnan--Shanghai--Xian--Beijing. The average temperture is around 20C. It is generally mild and pleasant, may be a little hot in Yunnan and Shanghai. Summer clothes are still be OK at that time. Well, you can also bring a piece of jacket in case the temperature has a suddenly fall .