It's freezing in Hong Kong - you will need at least one or two jumpers and jackets. That's just for the airconditioning most of the year though! (not kidding - the aircon here is set several degrees lower than comfort level, for some unknown reason, I keep a fan-heater in my office to counteract it).
Outside the temp varies from very hot and very humid (about 6 months of the year) to warm and humid (about 3 months of the year) to cool and pleasant (about 2 months) to 'quite nippy' ~ 1 month. Never goes below freezing but certainly gets cold enough for a light jacket (not the full-scale ski-resort type fur coats, hat and scarves the locals wear, but a jacket is fine). Abit like November or May in the UK.