The best time to visit Namibia is during the winter months, which is the British summer, when the weather is not too hot and there is no rain. The rainy season usually starts in mid-November.
The summer months (British winter), can be very hot and humid and there is a reasonable chance of rain. Namibia has one rainy season which begins in mid-November and runs through to mid-March. However, in comparison to many other African countries, Namibia is never especially wet.