Much talk around about the ‘Black South Easter’ that is expected to hit Cape Town over the next 36 hours or so, bringing with it high winds, dark clouds and much rain. And right from the outset, it should be pointed out that this nomenclature isn’t a racist thing. We don’t have an alternative ‘White South Easter’ which lives very comfortably in Constantia, happily subsisting off its ill-gotten, pre-94 gains and complaining about the ANC. No, this is so named because of the threatening colour of the clouds – a kind of meteorological Swart Gevaar, if you wish to continue the rather tenuous analogy.
The braai-ruining South Easter or ‘Cape Doctor’ which is usually prevalent in Cape Town from October through to (at least) December is due to a pressure area called the South Atlantic High (SAH) which sits just off the Cape coast and fairly regularly joins up with its equally high friend in Durban. These guys hang around together, being high, giggling at nothing in particular, eating Pringles and forming a ridge of high pressure below South Africa, bringing with them the warm Cape Doctor, which, despite its reputation for blowing patio chairs over in Vredehoek, is actually a fair weather wind.
All good so far? Fantastic.
So what goes wrong in this Black South Easter scenario, which is responsible for such nastiness as the great Laingsburg Flood?
At first the rain was gentle as a result of a low pressure system. But from Saturday afternoon to Sunday a high pressure system brought heavy thunder showers to the catchment area. Up to 425 mm rainfall was recorded that week-end, whereas the normal rainfall per annum is only 175 mm.
Well, despite their insistence that a high pressure system was solely to blame, it was actually the interaction between that high pressure system and what’s called a Cut-Off Low pressure area. Please don’t think for a moment that we’re talking about the usual mild-mannered inland low pressure trough that sits over the Karoo in summer here. No, this puppy is a deep low pressure area and it would much rather be with its mates down towards Antarctica at this time of year. Sadly, our South Atlantic High is so out of it that he’s joined up with his Bru from Durbs and unwittingly separated the low from his friends. Awkward.
Let’s explain what’s going on by transposing this situation into a bar room scenario. It would be a bit touch and go.
Ideally, the low pressure area would note the obviously wasted state of the South Atlantic High, politely point out the awkward social situation that had occurred – “Sorry dude, I just need to slip past, please” – and things would be quickly resolved.
Sadly though, meteorological pressure areas are unable to communicate with one another – or anyone else for that matter – and the angry young low has been doing Jägerbombs since lunchtime. He lets fly with everything he’s got, dragging the warm air from our high friends, chucking in some filthy black clouds and several inches of precipitation in his annoyance at not being allowed to sit with his mates over at the other side of the pub.
Fortunately, all this bluster doesn’t last for very long. Whereas a normal winter low pressure area would go on for a few days, the cut off low soon runs out of energy and falls down drunk at the bar. The ridge of high pressure looks on, grinning: “Dude, he totally fell over,” and gets on with clearing the dark clouds over the Mother City. That’s why Sunday actually looks quite nice and summer returns on Monday, when we’re all back at work.
If the forecast is to be believed, we’re in for a lot of rain from Friday evening through into Saturday. So do stay safe and remember these numbers in case of emergency.