What's the weather like going to Rizhao on September 4 and 5? Can you go to sea?

I think so, because we went in the middle and late August, and the weather was very hot. Things to bring: anti-mosquito bites, antidiarrheal drugs (eat seafood just in case), swimsuits and the like, food on the road, changed clothes, umbrella, sunscreen, mobile phone camera, charger, and most importantly, don't forget to bring money. If you plan to buy seafood, you'd better go to the wholesale market, which is cheap and enough (don't buy things that stand on the street, there will be a scale of 562; Supermarkets are heavy enough, nearly twice as expensive as wholesale markets), and that's all I can offer you for reference.