What is the humidity like in Shanghai and Beijing in August and how much rain is there likely to be.

Averagely, the humidity of Shanghai in Aug. is around 81% and that in Beijing is 77%.
The average rainfall in Beijing is 160 mm and the rainy days shall be around 12 days. I have to remind you that it will still be during Beijing's rainy season.

The rainfall in Shanghai is 230 mm and the rainy days may reach 13 days.