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When and where do tornadoes occur in South Africa

Occurrence in South Africa

Tornadoes can occur basically anywhere where a thunderstorm is possible. From an analysis of the occurrence of South African tornadoes it became clear that most of them have been observed in Gauteng, the Free State, KwaZulu-Natal (along a line from Pietermaritzburg to Ladysmith) and the northern region of the former Transkei. In figure 1 the eastern part of the country is depicted, showing the more significant events (F2 and F3) from 1905 to 1997.

Some 65% of the South African tornadoes are classified as F0 or F1 (light damage), while more than 90% are classified as F0, F1 or F2 (considerable damage) or less. The tornado which occurred at Harrismith on 15 November 1998 was classified as F2 and the Mount Ayliff tornado which occurred in the Eastern Cape on 18 January 1999 was classified as F4.

Tornadoes can occur basically anywhere where a thunderstorm is possible. From an analysis of the occurrence of South African tornadoes it became clear that most of them have been observed in Gauteng, the Free State, KwaZulu-Natal (along a line from Pietermaritzburg to Ladysmith) and the northern region of the former Transkei. There seems to be a preference to mountainous areas.

tornado_locations

Seasonal Distribution

The seasonal distribution of South African tornadoes is given in figure 2. Most of the events occur in mid-summer from November to January, although a large number of tornadoes have occurred in spring and early summer (September and October) and in the late summer and autumn (February to May). It is also worth mentioning that most tornado events (for which the time of the day were available) occurred in the late afternoon or early evening, typically between 16:00 and 19:00.

tornado_distribution

Forecasting Tornadoes

Meteorologists rely on weather radar to provide information on developing storms. Currently in the USA, only a 20-minutes before touchdown prediction is possible by identifying the so-called vortex signature of the tornado on radar.
Storm structure can provide clues about the existence of a tornado, clearly shown in the radar images for the Harrismith tornado. The Bow echo shape in the Harrismith area is typical of severe storms.

 

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