Contrary to popular belief, tornadoes are more common in South Africa than what is generally perceived, although the probability of them occurring is still very low.
Some of the destruction caused by the Tongaat tornado in KwaZulu-Natal on Monday afternoon, 3 June. Photo: Reaction Unit South Africa, Facebook.
CLIMATE NEWS - The tornado that struck Tongaat in KwaZulu-Natal (KZN) on Monday 3 June, has been rated EF3 on the Enhanced Fujita scale.
The South African Weather Service (SAWS) reached this conclusion after several damage factors were considered to assess the impact of the tornado in the area and further down the KZN coastline.
Considering these key indicators, and the estimated wind speeds, the EF3 rating places the tornado in the middle of the Enhanced Fujita scale.
An EF3 tornado is defined by windspeeds of between 225 and 265km, and causing severe damage. This include roofs and walls blown out of house frames, all trees in its path uprooted, the destruction of the upper floor of two-storey homes, and large vehicles blown from their original position.
The scale features 6 ratings - 0 to 6 - ranging from EF0 that causes "minor" damage, right through to EF6 that is defined as causing "incredible" damage with all buildings in its path destroyed leaving only concrete foundations in its wake and vehicles twisted and thrown away.
Enhanced Fujita (EF) scale wind speeds. Source: National Oceanic and Atmospheric Administration (NOAA), 2024.
One of the highest-rated tornadoes in South African recorded history was the Welkom tornado of 20 March 1990, rated as an F4 on the Fujita scale, resulting in damage to 4000 homes, and was one of the costliest in history. In 1999, an F4 tornado struck Mount Ayliff. This tornado threw cars and trucks into the air and left 95% of the population in the area homeless.
Most tornadoes in South Africa are WEAK, with a low EF rating of 0 to 2. The stronger and more destructive tornadoes (EF3 and EF4) occur every decade or so.
A social media image of the tornado captured near Tongaat on Monday afternoon, 3 June. Source: Facebook
What is a tornado?
A tornado is a violently rotating column of air that develops from the cloud base of a severe thunderstorm and extends to the ground (as seen above. Most tornadoes develop from strong and violent thunderstorms called supercell thunderstorms.
Tornadoes are the most formidable windstorms on earth and unleash devastating destruction along their trajectories.
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Tornadoes typically form in environments where certain atmospheric conditions come together. Some factors include wind shear, which involves significant changes in wind speed and direction with altitude, and atmospheric instability, where warm, moist air near the ground is overlaid by cooler, drier air aloft.
Additionally, systems like cold fronts or cut-off lows help the warm, moist air to rise. Sufficient moisture in the lower atmosphere is also necessary to fuel the thunderstorms that can produce tornadoes.
Contrary to popular belief, tornadoes are more common in South Africa than what is generally perceived (see below) although the probability of them occurring is still very low. Most tornadoes in the previous century (1905-1999) occurred over the eastern provinces, especially around Gauteng and KwaZulu-Natal.
Distribution and probability of tornadoes in SA for the period 1905-1999. Source: Goliger AM, Milford RV, Adam BF and Edwards M (1997) Inkanyamba - Tornadoes in South Africa. United Litho, ISBN 0-7988- 5417-0; De Coning E, Adam BF (1997), Weather Forecasting Research Programme, WaterSA- The tornadic thunderstorm events during the 1998-1999 South African Summer.
How it developed on 3 June
SAWS says a line of thunderstorms developed late-morning on 3 June along the border of the Free State and KZN ahead of a well-developed cut-off low-pressure system situated over the western interior of South Africa. Cold and dry air swept in from the western parts of the country to the central interior, while the eastern parts, particularly KZN, experienced warm and moist atmospheric conditions aiding in the development of severe thunderstorms where these cold and warm airmasses met.
In addition to this, strong low-level wind shear (wind shear refers to the change in wind speed and direction with height) was present over the coast and interior of KwaZulu-Natal ahead of the line of severe thunderstorms. This process of shifting or changing winds in the lower levels of the atmosphere, as the line of severe storms moved across parts of the province, was one of the primary contributing factors in the development of the supercell thunderstorms and tornadoes.
A rdar image of the supercell thunderstorm on 3 June with its hook echo and possible debris ball indicated. Source: SAWS Durban radar, 2024.
The Tongaat wedge tornado
The SAWS issued a media release on Tuesday, 4 June 2024, stating that at least two tornadoes were confirmed in KZN on Monday afternoon, 3 June. One of the tornadoes, called a wedge tornado because its wider and larger than it is tall, resulted in severe damage in the oThongathi (Tongaat) area. An analysis of the Durban radar data revealed several features indicative of a supercell thunderstorm. Meteorologists rely on specific radar features to identify severe thunderstorms like supercells.
At least two thunderstorms could be classified as supercell thunderstorms, while another, despite exhibiting supercell characteristics, did not persist long enough to meet the required time criterion. A supercell thunderstorm is a severe type of thunderstorm that contains a rotating updraft (rising air) and can be identified using a weather radar with characteristic features such as the hook echo on the reflectivity field and a rotational signature (mesocyclone) on the Doppler velocity field.
Such thunderstorms are also known to produce tornadoes at times but not all. The thunderstorm that passed over Tongaat and produced a tornado was confirmed to be a supercell, with a hook echo (Figure 3), although it did lack the typical rotational signature on the Doppler velocity field due to various limitations of the radar data.
A wedge tornado is wider and larger than it is tall. Photo: Facebook
A tornado signature on the Doppler velocity field may at times be detected, although limitations exist including the proximity of the storm to the radar. No significant Doppler velocity signature was noted in this case despite its close proximity to the radar, however on the reflectivity field a possible tornadic signature know as a debris ball was noted (see Figure 3). Such signatures occur because of the debris (often including highly reflective material) that are picked up aloft by the tornado and thus result in a ball-shaped echo.
Debris balls are often associated with stronger tornadoes, EF3 or greater on the Enhanced Fujita Scale.
The supercell features developed from around 15:30 local time and dissipated at around 16:41, soon after moving off the coast.
Compiled by Senior Forecaster Wayne Venter and Christina Liesker of the University of Pretoria.
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