The South African Weather Service (SAWS) has confirmed that the disruptive rain which led to localised flooding across large parts of KwaZulu-Natal, was due to a landspout, not a tornado, as most people suspected.
Explaining the landspout event in the Inanda and Phoenix area, SAWS said apart from damage to property due to the heavy and persistent rain, there was also damage to housing structures due to the strong winds associated with the landspout phenomenon.
At this stage, SAWS said the severity of damage resulting from this event lies within the lower end of the Enhanced Fujita Scale (EF scale) used to assess storm damage due to landspouts, waterspouts and tornadoes.
Based on photographic evidence at hand, SAWS rates the event as an EF1, associated with wind gusts well in excess of 100 km/h.
“On first impression, landspouts and tornadoes do look very similar; both phenomena manifest themselves as a dark, spinning vortex or tube extending from the base of a cloud. Both phenomena have the capacity to cause wind damage.
“Tornadoes typically cause damage across a much greater range of the EF scale, from EF0 (minor damage) right up to EF5 (catastrophic damage), whilst wind damage due to landspouts or waterspouts tends to be much less severe,” SAWS said in a statement.
SAWS said while landspouts and tornadoes may look very similar, their formative processes are widely different.
It noted that the formation of a tornado requires a “parent thunderstorm”.
“Interestingly, there is no evidence to suggest that any electrical storms were active in the Inanda and Phoenix areas during mid-afternoon [on 27 June] when the landspout was observed. No eyewitnesses mentioned either lightning or thunder.
“Moreover, despite cloudy conditions - with rain being observed throughout much of the day at King Shaka International Airport (approximately 15km north-north east of Phoenix), no thunderstorms were observed,” SAWS said.
By contrast, SAWS said, a landspout can form simply by the interaction of two low-level airmasses moving in opposing directions.
“The air trapped along this narrow boundary is sometimes exposed to a twisting force, which can force the air column to twist or spin around a vertically orientated axis (this process is similar to the spinning action of a child’s “spinning top” toy). When this phenomenon occurs over a lake or ocean surface, it is called a waterspout.
“Waterspouts are commonly encountered along almost all coastlines worldwide. In South Africa, this phenomenon is relatively uncommon but is perhaps underreported by the public,” SAWS said, noting that a landspout was recently observed and documented in the Koperfontein area of the Western Cape on 4 June 2023.
SAWS also emphasised that due to the very localised, short-lived nature of landspouts and waterspouts, they cannot accurately be predicted beforehand.
However, it said forecasts based on the background ingredients required for landspout formation may help to identify days when formation of such phenomena are more or less likely.
SAWS has assured that it will further investigate this event with a view to releasing a more detailed report in the near future. – SAnews.gov.za
