January in Johannesburg is the rainiest and the cloudiest month of the year. In January, the weather in Johannesburg is typically warm. Average daily high temperature in January is about 25 degrees above zero. On average, Johannesburg has 13 rainy, 9 partly cloudy, 7 sunny, and 2 cloudy days in January. The rains are usually heavy. January as well as December is considered the most uncomfortable time to visit Johannesburg.