Important Issues:
El Nino development still in infant phase. The effect on rainfall will most probably not be typical El Nino, especially for November and December where rain is possible over the Summer Rainfall Area. Beware however for the second part of the season.
1. Current conditions:
Although good falls of rain occurred at the beginning of October over parts of the Summer Rainfall Area, was there a lack of follow on rain since then. Summer grain farmers in Mpumalanga were able to start planting but that is not the case in the Eastern Free State where the planting window, like in Mpumalanga, will expire towards the middle of November. It is still too early for plantings in the central to western parts where the normal planting date only commences in the second part of November.
The rainfall that occurred in October was in general weaker than expected and can this be seen as a serious deviation from forecasts. Very low night time temperatures with frost were also still experienced in the last 10 days of October over the eastern production areas. Colder conditions are also possible in the first week of November but frost is not expected.
The very hot and dry conditions in the Western Cape, interrupted by cooler conditions with rain, make the harvesting of winter grains problematic. Levels of storage dams started to drop following the very hot and windy conditions and less rainfall.
2. El Nino and Indian Ocean:
The see-saw effect of El Nino development continues because of an increased possibility for persistent El Nino development. This is not good news because development this late in the season can be very negative for rainfall in the second part of the season. There is however still no coupling between El Nino and climate systems and can the effect of El Nino pose a threat later in the season. Examples of very late developed El Nino’s are 1958/59, 1968/69, 1994/95 and 2014/15. All these seasons were marked by a drier second part of the season.
The Indian Ocean Dipole (IOD) Index also moved into the positive phase meaning a warming of the Indian Ocean more to the west or closer to the east African coastline. Forecasts however indicate only a very short lived event.
3. Expected rainfall and temperature conditions
3.1 Summer Rainfall Areas
With the weaker than expected rainfall conditions up until now as well as a lack of real El Nino development earlier in spring, are the chances for rainfall also lower in especially the second part of the season. With the Neutral ENSO conditions dominant until now can it still be responsible for relative good rainfall conditions for November and December, especially over the eastern parts of the country. Tropical moisture is in place over western Africa as also was experienced by rainfall in Namibia but it is still blocked to move south and south east by unfavourable conditions over Southern Africa with a High pressure dominant.
3.2 Winter Rainfall Areas
In contrast to previous expectations and forecasts are cold fronts still prominent over the Western Cape with light falls that is interchanged by heat wave conditions. It is expected to still continue for a while.
3.3 Namibia
It is expected that Namibia will also suffers from the negative effects of El Nino in mid- to late summer. Conditions for rain seem to improve from about the second part of November.
4. Summary and conclusions
El Nino development still lacking persistence but it is now showing stronger indications of development. There was up until now no coupling of El Nino with climate and weather systems. The Neutral state of ENSO is still expected to drive weather systems and can good falls of rain still be expected in the second part of November and December.
Against expectations is the rainy season still active in the Western Cape with light falls of rain. The Atlantic high pressure system is still dominant over the southern parts of the country. Johan van Den Berg - Santam
