Advisable month to visit Shenzhen after July 2013

I wanna visit Guangdong, Shenzhen after July 2013, within this year 2013, is it any advisable month I should visit? Why?
FYI, I was considering the best weather for me, due to Malaysia is hot whole year, if the weather at Shenzhen is much more cooler, lets said about 20-25c would be better ^^