The South African Weather Services (SAWS) said the heatwave affected Gauteng, Mpumalanga, the Free State, Northern Cape, Limpopo and North West.
Weather forecaster Kumsa Masizana said a heatwave was usually associated with temperatures remaining constant over a certain period.
She said that the dry air experienced since the weekend had brought the high temperatures.
“On Tuesday it will become partly cloudy in the afternoon and temperatures will go as high as 37°C. Temperatures will start to drop slightly on Wednesday, and we will possibly have partly cloudy conditions,” she said.
SAWS advised residents to stay hydrated, out of direct sunlight and limit physical outdoor activity between 11am and 3pm.
Masizana said the hot and rainy season had officially kicked in. In some areas, rain could be expected from Thursday, including in Tshwane.
“During this time of the year in October, there is usually very high temperatures and little rainfall.
“Our predicted forecast might change so we encourage people to keep track of our warning signs.”
According to Associate Professor of Physical Geography Jennifer Fitchett at the University of the Witwatersrand, most of South Africa’s seasonal rainfall occurred during the warmer summer months from October to March.
“October is an important period for farmers to begin planning when to sow crops such as maize, wheat and sunflowers for the growing season.
“October is also an important period for the tourism industry to think about water supplies for the upcoming summer holiday season,” Fitchett said.
She said research had shown that the record low rainfall was caused by the expansion of the Hadley cell, the circulation of air from the tropics to subtropics.
This expansion has changed the timing of summer rainfall caused by intensified high-pressure systems, leading to dry conditions and a southward shift of the westerly wind belt providing moisture for winter cold front rainfall.
Fitchett added that farmers needed to plan to select crops that can be sown later and would fully mature with less rainfall due to a late wet-season start.