When travelling, it's generally smart to pack in preparation for rain or any other conditions that may arise. The rainfall in Exeter is roughly less than Mthatha. You can assume this to be the case over the next 5 days.
You can imagine temperatures to be in the 26 °C range in January. The weather in Mthatha is generally hotter than Exeter's. As flight availability is subject to become more limited as peak season approaches it is ideal to book in a timely manner.