EXPLAINER | What caused Tuesday's windstorm?

Three provinces awoke to a trail of damage on Wednesday after a storm on Tuesday.

The weather event brought damaging winds, as well as some rain, to Gauteng, the Free State and the North West.

In Pretoria, a fire fanned by a windstorm engulfed about 90 shacks at the Kameeldrift informal settlement, affecting about 150 people. Parts of the city were left without power after a fire, suspected to have been caused by lightning, at the temporary Pyramid substation next to Rooiwal power station.

Free State EMS spokesperson Sipho Towa said there were a few incidents in the province, but no casualties.

“Heilbron had a garage roof that the wind blew off, three power poles and a power box caught fire, and Vredefort had a few houses in Mokwallo that were taken by the storm. A house roof was also blown away in Parys,” he said.

According to the SA Weather Service (Saws), radar and satellite remote sensing data provided little or no indication of the severity of such storms.

“A feature which proved to be significant was that, given the very dry conditions at the surface, the convective cloud base of thunderstorms was at an abnormally high altitude above the ground.”

Saws said while this type of storm development can occur at any time of the year, early summer storms are notorious for strong, damaging winds caused by dry microbursts.

These storms are not typically associated with much rainfall, hence they are called dry thunderstorms.

What is a dry microburst?

This is a localised column of sinking air (also known as a downdraft) within a thunderstorm and is usually less than or equal to 4km in diameter.

Microbursts can cause extensive damage upon reaching the Earth’s surface and can be life-threatening.

“In the case of a dry microburst, the precipitation evaporates aloft within the downdraft, causing the downdraft air to become colder and denser, thus accelerating the cold air towards the ground, under the influence of gravity,” said Saws.

This phenomenon is typically associated with high cloud-base thunderstorms and is capable of uprooting trees and roofs, it added. 

Saws observed that wind speed exceeded 50 knots (114km/h) in Harrismith in the Free State between 4.15pm and 4.35pm, which is consistent with the typical strength of a dry microburst. 

“The public is urged to remain vigilant and follow weather updates on radio, television, Facebook and X.” 

Meteorologist Lehlohonolo Thobela said it is the season in which to expect thunderstorms, especially in the central and eastern parts of South Africa.

As the country moves into summer, expect thunderstorms with damaging winds, heavy rain and hail, depending on where you reside, he added.

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