The rains come in two spells: short rains in November and December, usually an afternoon downpour that clears, and long rains from mid-March through May, which are heavier and more persistent.
The green season is badly undersold. The country transforms — plains turn emerald, dust disappears, the light after a storm is spectacular, and the birding is at its peak with European and Asian migrants adding several hundred species. Many animals give birth now, so there are young everywhere, and predators follow them.
The trade-offs are honest ones: grass is longer so some animals are harder to spot, black cotton soil can make tracks difficult, and a few remote camps close entirely in April and May. In return the parks are quiet, you often have a sighting to yourself, and rates fall by a third or more. November, December and early March are the sweet spot — green, but not properly wet.