The SAWDOS received the following reports of waterspouts observed in the Durban area:
(A) Kamcilla Pillay from the Daily News writes: We received these pictures from a reader who was curious about these "water sprouts" and I wanted to find out what they were and when and why they occurred.
Do you have any information on them, or perhaps someone I can contact?
(B) Ross Murray writes: Have heard a few reports of a Water spout sighted off La Mercy on Saturday afternoon.
Do not have any photos yet, sure someone will have some pic/video.
SAWDOS: A waterspout is an intense columnar vortex (usually appearing as a funnel-shaped cloud) that occurs over a body of water and is connected to a cumuliform cloud. In the common form, it is a non-supercell "tornado" over water. While it is often weaker than most of its land counterparts, stronger versions do occur. Waterspouts do not suck up water; the water seen in the main funnel cloud is actually water droplets formed by condensation. Waterspouts have a five-part life cycle: formation of a dark spot on the water surface, spiral pattern on the water surface, formation of a spray ring, development of the visible condensation funnel, and ultimately decay.
Waterspouts exist on a microscale, where their environment is less than two kilometers in width. The cloud from which they develop can be as innocuous as a moderate cumulus, or as great as a supercell. While some waterspouts are strong and tornadic in nature, most are much weaker and caused by different atmospheric dynamics. They normally develop in moisture-laden environments as their parent clouds are in the process of development, and it is theorized that they spin up as they move up the surface boundary from the horizontal shear near the surface, and then stretch upwards to the cloud once the low level shear vortex aligns with a developing cumulus cloud or thunderstorm.
Waterspouts that are not associated with a rotating updraft of a supercell thunderstorm are known as "non-tornadic" or "fair-weather waterspouts", and are by far the most common type. Fair-weather waterspouts occur in coastal waters and are associated with dark, flat-bottomed, developing convective cumulus towers. Waterspouts of this type rapidly develop and dissipate, having life cycles shorter than 20 minutes.
There are five stages to the waterspout life cycle. Initially, a prominent circular, light-colored disk appears on the surface of the water, surrounded by a larger dark area of indeterminate shape. After the formation of these colored disks on the water, a pattern of light and dark-colored spiral bands develop from the dark spot on the water surface. Then, a dense annulus of sea spray, called a cascade, appears around the dark spot with what appears to be an eye. Eventually, the waterspout becomes a visible funnel from the water surface to the overhead cloud. The spray vortex can rise to a height of several hundred feet or more and often creates a visible wake and an associated wave train as it moves. Eventually, the funnel and spray vortex begin to dissipate as the inflow of warm air into the vortex weakens, ending the waterspout's life cycle.
Waterspouts do occur each year in the Durban area. Waterspouts in the Durban area are often confused with tornadoes as they have similar features, including a funnel extending from a dark rotating cloud. Waterspouts in the Durban area only occur over the ocean in Spring and Summer and usually dissipate when they get near to land. Waterspouts do not frequently occur in the Durban area. There is normally between 2 - 3 waterspouts observed along the Kwazulu Natal coast.
Looking at the two images provided it is my opinion that both reflect "non-tornadic" or "fair-weather waterspouts" However it is difficult to come to a definite conclusion with only two photos at hand.
On the 8 April 2010 a waterspout was observed in the Sani Valley over a dam in the Himeville area of Kwazulu Natal. On the 31 January 2011 at 19h10 a waterspout was observed in the Bluff area of Durban.
Non tornadic waterspouts are most frequently seen in tropical and sub-tropical climates. Waterspouts have long been recognized as serious marine hazards. Stronger waterspouts are usually quite dangerous, posing threats to ships, planes, helicopters, and swimmers.
It is recommended that the public keep a considerable distance from these phenomena, and to always be on alert.
Sources:
Wikipedia
HAMNET
SA Weather and Disaster Information Service
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