[KZN] SA Weather Service issues heavy rain warning

Rayne said:
Well ****.

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Nice analysis! The models have been showing all of these scenarios (in various charts), and it's great to see them all summarised.

However this is only one day's outlook (Thurs 17th), and a developing cutoff-low will produce widespread unusual weather conditions between Fri 18th and Sun 20th. Cumulative rainfall totals in KZN could reach 200mm.

Edit: The other thing they forgot to include is the cold conditions likely to move in, with snow likely over the Drakensberg:
southafricasnownext3days[20260919_0600].jpg
 
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Hopefully it will just continue on a constant pace, hoping we don't get cloud bursts of 30mm or more in an hour over the next two days.
 
Dylan_G said:
ngl, I still don't know what a cut-off low is.
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I too used to wonder about that.

But then one fateful day I saw Margate's water infrastructure floating all the way down here past Port Shepstone beach with my own eyes.

That same day I also saw my walls collapse, neighboring groundwater split apart a concrete slab which then lifted downpipes which then lifted my gutters which then broke 3 rows of rooftiles which then caused leakage in my office, laundry, bathroom and kitchen.

I also got the experience the fun fun activity of shoveling displaced sand blockages away from seeping holes and gates in knee-deep water for hours on end in this lovely weather barefoot becuace **** know where my flops went never found them to this day and in my onderbroekie because you can only waste so many clothes until you have to go outside and ruin them again all in order to prevent water entering the house.

The next day I learned that we had 400mm in less than 2 days and in Durban more than 400 people died.

Now I know what it it. And now I pay attention.

Gave me a bit of PTSD to be honest.

Long story short is these things are hard to predict until they occur and can often be over and under-estimated but care should still be given.
 
Dylan_G said:
ngl, I still don't know what a cut-off low is.
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A long topic! The most basic summary is that a cutoff low (COL) is like the cold mid-latitude version of a warm tropical cyclone. We get many cold-fronts passing south during the year, and sometimes cold upper air 'buds' off to form a closed system (hence the term cutoff low). A combination of moisture inflows with strong surface winds, deep upper instability and convective thunderstorms, and slow drifting motion can cause torrential amounts of rain (100mm per day) to accumulate over a given location.

COLs are fairly hard to track (like cyclones), and can have varying effects around the system, making forecasts tricky. Because they are complex 3-dimensional structures, it is impossible to give a single chart or image that shows all of the features. For example surface and upper level winds are often in completely opposite directions, temperature gradients and moisture inflows may be inconsistent, etc. A surface (ship) synoptic chart tells you absolute nothing about the upper level developments associated with a COL.

P.S. The Cape Town name for a cutoff-low is a Black South Easter, indicating that it is unusual to get rain from that direction (summers are normally dry here).
 
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