Now I've basically started wearing short sleeves here, so I feel hot when I go out without rain.
You can wear chiffon shirts and so on. If you wear sleeveless clothes, it is recommended to add a thin coat (you can wear it when the air conditioner in shopping malls and buses is cold). Forget jeans. I wear shorts now.
If you are not particularly afraid of the cold, just wear a coat at will in the morning and evening. It may rain during Tomb-Sweeping Day. You'd better look at the temperature in Zhuhai in the last seven days the day before you come.