Mostly it's cool and comfortable.Highest temperature is about 27 celsius,and lowest about 18 celsius, almost half days shinning, half are heavy rain. I think long sleeve shirt and jeans are enough. If you donot like heavy luggage, you can buy umbrella in Shanhai, there are a lot of different kinds of umbrellas in the market and shops. Most of them are quality and cheap. Wish you have a happy trip.