Month by month
Tsavo in December
December is two months wearing one name. Until roughly the 20th it is the wettest, greenest, quietest stretch of the whole calendar; after that the coast fills for Christmas and the safari traffic follows it inland, storms or not.
If you only want the answer
December splits in half: a soaked and silent opening act at 83 mm over 17 rain days, the wettest line on the card, then a festive rush from just before Christmas with lodge prices to match. Decide which December you are actually booking.
The wettest card of the year
No month in the Voi normals carries more rain than December's 83 mm, spread across 17 rain days, with highs of 29.1°C. Even so, the rain mostly falls in short heavy bursts, and the park between them is saturated green, loud with birdsong and largely empty of vehicles in the first half of the month.
It shares nearly everything with November, and the honest difference is a single item: from about the third week, people. The migration nights over the Ngulia escarpment continue into December too, for anyone extending that trip.
The festive turn
Kenya's coast hits its own high season at Christmas, the resort add-on safaris restart in force, and the lodges respond with festive supplements that make late December some of the priciest nights of the Tsavo year. The long Kenyan school vacation is running through the month as well, which adds domestic traffic on top.
None of this changes the weather; you can absolutely spend a stormy, green, expensive Boxing Day at a full lodge.
Booking the two halves
The first half needs almost no lead time and gives you real leverage on rates; the festive week wants a reservation by September at the popular houses. If wildlife photography is the goal, aim earlier in the month when the light is dramatic and the sightlines, while thick, are all yours.
Birders get Tsavo West's 600-plus species list at full strength now, and Lake Jipe in the far south repays the long wet drive better than anywhere else in either park.