It’s the season for thunderstorms and severe thunderstorms, so storms like the one in Johannesburg on Monday are by no means unusual and are to be expected, the South African Weather Service said.
It’s the season for thunderstorms and severe thunderstorms, so storms like the one in Johannesburg on Monday are by no means unusual and are to be expected, the South African Weather Service (SAWS) said.
Isolated incidents, such as the severe hailstorm that pummelled parts of Johannesburg with golf ball-sized hailstones, cannot directly be attributed to climate change, said Tshepho Ngobeni, the senior manager of disaster risk reduction at the weather service.
He was speaking at a briefing the meteorological service hosted on recent severe weather events, the effect of El Niño and climate change, which was held at the National Press Club in Pretoria on Thursday.
Ngobeni drew on a recent article by Andries Kruger, the chief scientist at the weather service’s climate service department, which contained excerpts from the Intergovernmental Panel on Climate Change’s sixth assessment report.
“Regarding the current state of the climate, the scale of recent changes across the climate system as a whole — and the present state of many aspects of the climate system — are unprecedented over many centuries to many thousands of years,” he said, citing the article.
On possible climate futures, “many changes in the climate system become larger in direct relation to increasing global warming. They include increases in the frequency and intensity of hot extremes, marine heatwaves, heavy precipitation, and, in some regions, agricultural and ecological droughts; an increase in the proportion of intense tropical cyclones; and reductions in Arctic sea ice, snow cover and permafrost.”
Ngobeni said the conclusion “could be therefore that an increased probability of ‘normal’ severe weather events is most likely to be the result of climate change”.
“However, this does not mean that specific severe weather events can solely be attributed to climate change. Specifically, the storm in question occurred due to a range of factors favourable for its development.”
Inundated with questions
On the severe thunderstorm that lashed the southern parts of Gauteng and parts of Mpumalanga on Monday night, Ngobeni said: “We were saddened to see members of the public counting their losses after the thunderstorm in question ran riot, unleashing a hailstorm in the City of Johannesburg in Gauteng and a tornado in the Lekwa local municipality in Mpumalanga. In Johannesburg, Midrand was the hardest hit.”
By late Monday evening, and well into the following day, social media platforms were awash with graphic imagery of vehicles with dented bodies and shattered windshields, and homes with broken windows.
“Naturally, in the aftermath of such weather events, questions abound,” said Ngobeni, noting how the weather service has been inundated with questions from the media since Monday, which probably “mirror those preoccupying the public at large”.
On the steps it took ahead of and during the severe weather event, Ngobeni said that early on Monday evening, it issued a yellow level two impact-based warning, or a high likelihood of minor impacts, for severe thunderstorms for districts and metropolitan municipal areas such as Govan Mbeki district in Mpumalanga and the City of Johannesburg.
“In the warning in question, it was indicated that the SAWS’ observations showed severe
thunderstorms over the southern parts of Mpumalanga, the City of Johannesburg and
Ekurhuleni, with the possibility of heavy downpours, floods and a large amount of small hail. The public was instructed to be aware that any combination of hail, strong winds, heavy rain and/or excessive lightning as those could accompany the storms.”
He also said the weather outlook that the weather service shared on its communication platforms on Monday morning predicted isolated thunder showers over the eastern parts of the country, which included Gauteng and Mpumalanga. This was consistent with the regional weather forecast issued the previous day.
He also made reference to people’s confusion wondering why the warning was so closely timed to the event. “This is a valid and critical concern. Severe thunderstorms are different from other forms of severe weather such as snow, heavy rain, gales and very rough seas, which can be predicted successfully and routinely well in advance with the help of numeric weather prediction models.
“The 104 warnings of varying levels that we issued between January and August this year,
coupled with the 27 media releases “that we have issued from January to date, ahead of
severe weather events across the country bear testimony to this assertion”.
Severe thunderstorms, by contrast, are a “different ball game altogether”, he said. This phenomenon, as well as the specific location where it will occur, can seldom be predicted at long lead-times.
There are two main reasons. “The one is that severe thunderstorms are generally short-lived. The other is that individual storms tend to be much more localised. Typically, specialised short-period forecasts are the medium of choice for issuing severe thunderstorm warnings.”
These short-period forecasts are known in meteorology circles as the nowcasts. This is because their prediction lead-times can range from less than an hour to a few hours. “Due to the peculiar nature of severe thunderstorms, a warning can be issued as close to the actual event as less than an hour up to a couple of hours.”
This was the case on Monday when real-time observations of remotely-sensed data or
RADAR and satellite imagery made it possible for forecasters to identify southern Gauteng
as well as the Mpumalanga Highveld “to be at risk of severe storms quite close to the
eventual occurrence of those events”.
Liesl Dyson, associate professor in the department of geography, geoinformatics and meteorology at the University of Pretoria, told the Mail & Guardian that October and November have a high frequency of these severe storms to happen, “especially over the Highveld going into Mpumalanga, Joburg and further west into the North West province. It is a hotspot for severe thunderstorms and hail this time of the year.
“When it happens over a highly populated area like Midrand, there are a lot of observations of it. And then the damage was severe … If there’s lots of people staying in an area, you get more damage,” she said.
The size of the hail, however, does not occur every year. “I can’t say I know that we have hail the size of golf balls every year. It tends to be the extreme size of hail, but it has happened. For instance in November 2013, we had two days of severe hail that cost a lot of money in the insurance industry over specifically the highest populated areas of Gauteng.”
Moderate El Niño
On the seasonal prediction for the looming summer season, Christien Engelbrecht, the lead scientist for long-range prediction at the weather service, said the El Niño-Southern Oscillation (ENSO) is currently at moderate strength.
This El Niño event is predicted to continue throughout the summer season, into early autumn of 2024 where after ENSO-neutral conditions become the most likely state of ENSO. “In other words, we can expect that the El Niño event can have an impact on South Africa during our summer season of 2023-2024,” she said.
El Niño events are typically warmer and drier over Southern Africa during the summer
months. “However, current seasonal predictions indicate uncertainty for the typical drier conditions over the north-eastern parts of the country where the current prediction indicates low probabilities for above-normal rainfall. Over the remaining parts of the country below-normal rainfall is predicted.”
Current predictions of the El Niño event indicate that it can become a strong event during
the mid-summer months. “Temperature wise, the likelihood for warmer than normal conditions is high, with the highest chance over the interior regions of South Africa.”
Engelbrecht said that this leads to a high chance of heatwaves occurring over the interior parts of the country.