According to data from the South African Weather Service (SAWS), the rain will affect KwaZulu-Natal, Gauteng, Mpumalanga, eastern parts of the Free State and northern Lesotho.
"We are expecting a lot of moisture and cooler temperatures from that high pressure system," SAWS forecaster Victoria Nurse told News24.
The high pressure system is expected to develop by Friday afternoon and move eastward, driving cooler temperatures in the southern Cape and interior of the country.
SAWS forecast data predicts 60% rainfall in Johannesburg, Midrand and Pretoria on Saturday.
Rainfall for Durban is forecast at 80% as cooler air pushes in from the east.
Temperatures are expected to drop significantly but not enough to produce snow.
"There might be a light flurry of snow in Lesotho but no snow is expected in SA," said Nurse.
Typical weather
Last weekend, storms lashed Gauteng, resulting in flooding and hail.
Motorists found themselves stuck as roads succumbed to flash floods and the SAWS issued several storm weather warnings.
The northern parts of SA experience summer rainfall and Nurse said that the weather was typical for the time of year.
"It's normal for this time of year; we can expect these systems to come in and bring in rainfall and cloudy conditions."
SAWS regards a three forecast as a highly accurate, and, consequently, issued no warnings for the expected Saturday rainfall.
"It's a bit too far in advance to give warnings. Accuracy is high when forecasting the first three days and after four days, the accuracy drops.
"Saturday would be our day 4," said Nurse.
CORRECTION: This story has been updated to more accurately reflect the expected weather patterns.
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