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El Nino development less intense than expected but poses still a risk for drier conditions. South Africa

Current conditions: Rain continued over most of the Western Cape and adjacent Eastern Cape during September 2018.

Less rain than expected was recorded over the Summer Rainfall Area with only light and very isolated falls over the eastern parts of the country. Some rain in the drought stricken parts of the Eastern Cape was welcomed but more rain is needed to brake to effect of the drought. Very dry conditions continued over the southern parts of the Northern Cape and adjacent areas as well as the north western part of Limpopo.

Most summer crop farmers were able to do primary cultivations following the harvesting process and fields are ready to maximise infiltration of rainwater once it starts to rain. There are however areas where finance is a problem and no soil preparation is done up till now. The winter wheat crop in the Western Cape is heading in most cases for records yields following the very good distribution of rainfall during most of the growth cycle. Farmers will most probably start to harvest from about the second part of October. The very windy conditions are impacting negatively on the dry land winter crops in the Free State and rain is needed urgently.

2. El Nino and Indian Ocean​:

In contrast to previous forecasts is the pending El Nino now less certain. The warming of surface water in the Equatorial Pacific is less than forecasts indicated previously. The latest outlook is now for Neutral/weak El Nino. This change is very late in the season but there is still at least a 50% probability for El Nino conditions to occur. Why? Sub sea surface waters warmed in the past weeks and are warmer than normal up to about 200m below the surface in most of the Nino areas. This water is likely to reach the surface. Trade winds also slowed down and that is an indication of El Nino development.

The Indian Ocean Dipole Index also moved slightly into the positive mode, meaning that the warming of the Indian Ocean sea surface temperatures are more towards the western parts of the Ocean towards the Africa continent. Forecasts however indicate a relative short spell with low intensity.

3. Expected rainfall and temperature conditions​

3.1 Summer Rainfall Areas
The expected rapid El Nino development did not happen and together with this lack of action in development, decreases the probability for early rain. With a more neutral state of the ENSO it shifts the probability for summer rain more towards the normal starting dates. The forecasts are now for the start of the rainy season over the central to eastern parts from about the second part of October and later for the western parts. If rapid El Nino development is to commence in the next month it can then very negatively impact on rainfall for the midsummer. Although El Nino intensity will probably be weaker than initial indications can the timing of development increase the risk for lower rainfall conditions.

3.2 Winter Rainfall Areas
There are strong indications that the end of the rainfall season was reached towards the end of September with only a slight probability for further rain.

3.3 Namibia
It is expected that Namibia will also suffers from the negative effects of El Nino in midsummer and the timing of development of El Nino can also be responsible for an increased risk for lower rainfall conditions.

4. Summary and conclusions​

Rapid El Nino development did not occur as was forecasted and it is currently still in a neutral state. If development starts later in the season it can have very negative effects on rainfall. If it stays close to neutral it can result in more average conditions.

It seems that the very good winter rainfall season for the Western Cape is now about to stop with very little further rain expected. 

Johan Van Der Berg Santam Afgri


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