The weather service said the thunderstorms will be characterised by large hail, damaging winds and heavy downpours across the province.
On Tuesday, temperatures reached 34°C in Pretoria.
READ MORE: Heavy rains wreak havoc on Gauteng roads
In December last year, hundreds of people were displaced when a severe storm ripped through south of Johannesburg and the West Rand, damaging their houses and bulk infrastructure.
– African News Agency