The South African Weather Service (SAWS) is monitoring the development of the rain which is expected on Monday.
Widespread showers and thundershowers are expected until Wednesday in Gauteng, the eastern parts of North West, northern and eastern Free State, Limpopo, Mpumalanga and KwaZulu-Natal.
The weather service says there is potential for some areas to receive significant amounts of rainfall which may result in localised flooding.
Temperatures are expected to drop and it will be cold from late today over most of the eastern interior of the country until Thursday.
Snowfalls are also possible over the Lesotho mountains during this period. Conditions all round are set to improve from Thursday afternoon onwards.
The weather service has advised the public to take note of precautionary measures when encountering flooding.
If possible, stay indoors and off the roads, avoid crossing rivers and swollen streams where water is above your ankles. If trapped in a flooding situation while in a vehicle, rather abandon it and climb to higher ground.
In buildings, move valuables to a safe place above the expected flood level. Switch off electricity at the supply point to the building.
Abandon home immediately if evacuation is recommended by duly authorised officials, before access is cut off by flood water. Never drive on a road covered or obscured by water. If the vehicle stalls, leave it immediately and seek higher ground.
Be especially cautious at night when it is difficult to identify flood hazards. Listen to the radio or TV for warnings and obey the instructions from disaster management officials.
The weather service will continue to monitor any further developments relating to this weather system and will issue subsequent updates as required. Furthermore, the public is urged to regularly follow weather forecasts especially on electronic media.