December in Randburg, South Africa, brings average daily highs of 26°C and overnight lows of 15°C in the 2016–2025 historical record. Light clothing is a useful starting point, with room in the plan to pause indoors. Decide how much walking to fit into each day using the local forecast, rather than treating the monthly average as a limit.
In the record, at least 1 mm of rain or snow falls on 17 of 31 days on average, a daily chance of 53%. Give wet-weather alternatives a proper place in the itinerary. Arrange outdoor plans so you can move them between days, and pack a rain layer rather than relying on a completely dry run of weather.
The calculated day length, sunrise to sunset, averages about 14 hours. Sunshine averages 11 hours a day. The longer daylight window gives you more choice about when to be outside; it does not mean every part of the day will be sunny. Sunshine is a separate measure, and those hours need not arrive in one uninterrupted stretch.
Start with the places you most want to visit, then keep the order flexible enough to suit the weather. Check current opening hours and local transport before fixing long day trips. The climate record can help with pacing and packing, but it does not describe what is open during your stay.
January has an average daily high of 27°C, 1°C higher than December. Its historical rain-day chance is 45%, compared with 53% 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.