What will the weather be like in Beijing, Shanghai and Xian for the middle of September

In mid of Sep. Beijing and Xian has been in Autumn. The average temperature then could be about 20 C. You'd better take along long-sleeved shirts and light overcoats. Actually, it is a wonderful time to travel in Beijing and Xian with the pleasant temperature and mild sunshine as well as the beautiful Autumn scenery, especilly in Beijing. Besides, it might rain then, so to pay attention to the weather forecast is suggested when you are outing.
While, for Shanghai, it has the average temperature of 25 C. But the typhoons may bring heavy rain in their wake. So you'd better take along the rainy wear in case of the rainy days.