Dear Jiwoo,
I hope you can arrive at HK on 20 October (Sunday) or 21 October ( night on Monday). The weather of HK is dry and windy. There is no need for you to bring big coat. If you have time you can buy clothes in HK. Air pollution is serious especially at Mong Kok, Tsim Sha Tsui, Yau Ma Tai......etc. So you must bring cleaning milk, day cream and night cream.
See you in HK!
Best wishes!
Edith