Expect intenser storms in future
Many residents living in the coastal areas of Ndlambe may be curious to know what weather system resulted in the heavy rainfall, strong winds and associated damage on the night of Sunday August 7.
A deep low pressure system on both the surface and upper air, situated over the Ndlambe coastal region, combined with a strong ridging high pressure over the ocean, advected moist maritime air onto the coastline and the immediate adjacent interior.
This resulted in localised flooding (up to 120mm) and strong easterly wind gusts of up to 85.7km/h, which is just short of gale force. Older residents will recall the disastrous Port Alfred floods of 2012.
It is important not to confuse the “cut-off” low pressure system which gave rise to these floods with the current localised flooding.
A well-developed “cut-off” low system (also known as a Black South-Easter locally) can result in rainfall totals in excess of 500mm.
The record-breaking floods of Port Elizabeth (Gqeberha) in 1968 and the destruction of the Lower Baakens River valley will not be forgotten easily, where some elevated areas recorded up to 650mm over a 24-hour period.
Interestingly, the severe weather was accompanied by thunderstorm activity, which was caused by the easterly flow into the deep upper air low.
The convergence of air masses at high altitudes led to embedded, localised thunderstorms over the coastal belt, accounting for the patchy rainfall distribution.
Fortunately, in this case, the deep upper air low was not cut off by the oceanic high-pressure system and this allowed it to move past relatively quickly and fill up over the sea further to the east of Ndlambe.
Readers will know that coastal weather in SA is never stable for any length of time.
Travelling disturbances, which migrate up the coastline from west to east during the winter months, include coastal lows (forerunners of cold, rainy, and blustery frontal weather) and mid-latitude cyclones (cold and warm fronts).
The South African Weather Service (SAWS) had issued a Level 2 warning 48 hrs before the event, warning of disruptive rain and localised flooding with associated minor impacts.
Such SAWS weather warnings are disseminated via various media platforms, in particular social media, and are available to both the public and specialised disaster and emergency services in Ndlambe.
The new “impact-based” severe weather warning system was co-developed by SAWS and the National Disaster Management Centre.
The idea behind this system is to warn the public of possible impacts and not to describe meteorological parameters such as rainfall amount or wind strength.
The colour-coded matrix which was developed combines the level of impact with the likelihood of it occurring (see the diagram on the right).
Source: https://www.weathersa. co.za/home/forecastques
The most recent UN Climate Change Conference (COP 26) was held in Glasgow in 2021.
Reports from the conference underscore the now clear scientific link between climate change and an increase in severe weather events globally.
This is particularly relevant for SA, where leading climate scientists predict more rainfall over the eastern side of our
country, shorter in duration but much more intense, leading to more severe impacts on infrastructure and livelihoods.
So, residents of Ndlambe, to borrow the Boy Scout motto, Be Prepared!
Dr Des Pyle is a senior lecturer, Disaster Management, Stenden
South Africa www.stenden.ac.za
WEATHER WATCH will be a regular column in Talk of the Town, focused on climate and weather information that is important for people living in Ndlambe, particularly on the coast.