Are there any precautions for traveling to Shanghai, Hangzhou and Nanjing in early May?

After May Day, the weather was hot, and I basically put on my summer clothes, but it was still cold after the rain. Old people should put on more clothes and prepare coats. People are crowded around May Day, so take care of the elderly. From Shanghai to Chenghuang Temple, there are fennel beans, Nanxiang steamed buns, sugar pear paste, green corridor snacks, Hangzhou West Lake vinegar fish, lotus root starch and hand-peeled walnuts, and Nanjing salted duck.