A supercell thunderstorm swept through South Africa's KwaZulu-Natal Province on October 10, 2017, dropping unprecedented rain on Durban, the region's main city and home to one of the busiest ports in Africa. At least 6 people were killed in Durban and 2 in Nquthu. Several people are still missing.
On October 9, 2017, a line of thunderstorms developed east of a cut-off low pressure system which was situated over the western parts of the country. These storms developed through the central parts of the North West and northern Free State and then started moving eastwards.
Due to prevailing favorable conditions (including abundant low-level moisture and strongly sheared airflow in the lower portion of the storms), some of these storms developed into supercell thunderstorms. Supercell storms are the most intense class of thunderstorm and are characterised by a deep rotating updraft, are generally very long-lived (a lifespan of a few hours) and are associated with some sort of severe weather (one or more of large hail, tornadoes, strong winds and urban flooding) in at least 90% of cases.
Severe thunderstorms with heavy downpours, strong damaging winds and large hail, hit parts of Gauteng and surrounding provinces on the afternoon of October 9, 2017, South African Weather Service said.
Areas that were most affected were the West Rand District, City of Johannesburg and Ekurhuleni Metropolitan Municipalities. There were also 2 sightings of tornadoes in Ruimsig (adjacent to Roodepoort and Krugersdorp) and Eloff, near Delmas (Mpumalanga).
Other provinces affected were the eastern parts of North, West, eastern Free State, KwaZulu-Natal, Mpumalanga, and Limpopo. Extremely large hail (golf ball to tennis ball size) was also reported near Krugersdorp.
Elsewhere in the Free State, a tornado was also observed near Bethulie on October 9. Extensive damage to property was reported, which included the Cradlestone Shopping Mall in Roodepoort, where a roof partially collapsed, as well as numerous formal and informal dwellings which were completely destroyed. This resulted in more 100 people being displaced from their homes. Some roofs were ripped off residential dwellings and small office complexes in Krugersdorp and Roodepoort.
Major roads were also affected by the flooding and resultant debris that were caused by the storm.
The storm forced the closure of the Port of Durban, one of the busiest in Africa whose authorities said three vessels were grounded while others broke mooring lines and drifted in the channel. Port manager Moshe Motlohi told Reuters on October 11 it was still too early to assess the extent or costs of damages to the port, adding they could not estimate when the port would be opened again.
In South Durban, the storm registered the highest daily rainfall figures for South Durban since records began, SAWC said. Its Merebank station at the old airport site recorded 108 mm (4.25 inches) within 24 hours on Monday and Tuesday, October 10, breaking the previous record of 105 mm (4.13 inches) set on October 30, 1985.
The 108 mm represents approximately one-tenth the average annual rainfall for the province which fell over a period of six to eight hours. Other rainfall recorded in the greater Durban area showed 58 mm (2.28 inches) at King Shaka International Airport, 69 mm (2.71 inches) at Mount Edgecombe and 17 mm (0.66 inches) at Nagle Dam.
In the interior, a new rainfall record was set at Ixopo where weather stations registered 58 mm (2.28 inches), breaking the previous highest daily rainfall of 38.6 mm (1.51 inches) set on October 28, 2014. Kokstad recorded 36 mm (1.41 inches) and it's lowest maximum daily temperature of 8.5 °C (47.3 °F). Emerald Dale recorded 32 mm (1.25 inches), Pietermaritzburg 15 mm (0.59 inches), Oribi airport 16 mm (0.62 inches), and Cedara 14 mm (0.55 inches).
On the KZN South Coast which was also heavily hit with a number of bridges under water and roads washed away, Margate registered 51 mm (2 inches), Paddock (outside Port Shepstone) 81 mm (3.18 inches), Pennington South 68 mm (2.67 inches) and Port Edward 25 mm (0.98 inches), SAWC said, as reported by IOL.
Dozens of buildings were damaged and local authorities say that at least 500 people have been displaced across the province. Many of the displaced communities have been temporarily accommodated in community halls and buildings.
Another cold front is expected to hit the region on Friday, October 13.
Featured image: A container ship blocked Durban harbour after drifting away during strong storm on October 10, 2017. Credit: Blue Security