Here is a website for SA weather. I hope you find it satisfactory.
Otherwise, much of sub sahara weather is governed by the movement of the ITCZ which is pretty easy to track and forecast - in general terms-on a satellite weather website.
I would suggest that you are prepared to tank fuel as you find it, just to be on the safe side for weather and for the possible shortage or breakdown of equipment at your next port of call. Do not necessarily believe them if you call ahead to the less sophiscticated places and they tell you it is a nice day and they have lots of Jet A1.and that all the equipment is working. Things break very easily in Africa and lock up your aircraft at night and consider finding a security guard for it.
Aviation - South African Weather Service