December in Hong Kong, Hong Kong, brings average daily highs of 20°C and overnight lows of 15°C in the 2016–2025 historical record. Pack clothes you can layer as conditions change. The average leaves room for both warmer and cooler days, so a flexible walking plan is more useful than deciding every outdoor stop before you arrive.
In the record, at least 1 mm of rain or snow falls on 2 of 31 days on average, a daily chance of 8%. Rain has been relatively infrequent in this record, which leaves more scope for an outdoor plan. Still keep an alternative for a wet day: a low monthly average cannot tell you when the rain will arrive.
The calculated day length, sunrise to sunset, averages about 11 hours. Sunshine averages 8 hours a day. Use the daylight window to plan the length of excursions, and check local sunrise and sunset times for the dates of your stay. Sunshine is a separate measure, and those hours need not arrive in one uninterrupted stretch.
For nature trips or walks, keep the longest outings movable and check route conditions locally; a monthly climate average cannot establish whether a particular path is accessible. If the coast is part of your plan, check water conditions separately. Air temperature and sunshine do not establish swimming conditions, surf quality or diving visibility.
January has an average daily high of 19°C, 1°C lower than December. Its historical rain-day chance is 15%, compared with 8% this month. If your dates are flexible, compare those trade-offs with the kind of days you want. Neither set of averages predicts the conditions of one particular holiday.