El Nino likely to weaken further with a >50% probability of ENSO (El Nino Southern Oscillation)-neutral conditions for the summer of 2019/20. Indian Ocean will most probably the main driver for below average rainfall conditions in the spring and early summer. ENSO-neutral conditions will favour good mid- to late summer rainfall.
1.Current conditions
The winter of 2019 will be remembered as one of the mildest winters on record in South Africa. Although frost occurred, was the number of frost days well below the long term average number of days.
Maize farmers nearing the end of the harvesting process but the lack of cold conditions resulted in a very slow drying rate of grains. Yields varied between crop failures (early planted maize) to above average yields.
Winter grain crops in the Western Cape are in general still looking promising but it seems that the rainy season is starting to slow down with September, the make-or-break month is still ahead. With high day time temperatures is the water use extremely high and drought damage may start to occur.
Water levels of most storage dams in the country is good for this time of the year. It is only the Vaaldam (62.8%) that is much lower compared to 2018 the same time (96%) and dams in the Eastern Cape that is on average lower compared to 2018. The Clanwilliamdam in the Western Cape increased its level from about 30% a few weeks ago to close to 100%. The Theewaterskloofdam is also now 70% of capacity.
2. El Nino and Indian Ocean
Three of the four Nino-areas are already since the beginning of July 2019 within the +0.5˚C and -0.5˚C range, indicating a gradual shift away from El Nino towards Neutral. It is only the Nino4-area, (nearest to Australia) that is still outside the neutral range (0.8˚C warmer than average). Most forecasts are opting for neutral conditions to remain dominant for the rest of 2019 and first part of 2020 with only a 30% probability of El Nino to redevelop.
The Southern Oscillation Index that is the measure of coupling between surface and weather systems, is for the first time the recent past six months not in an El Nino-type of mode but neutral.
Warming of the western Indian Ocean resulted in the development of a positive Indian Ocean Dipole Index (IOD) for at least the past 6 weeks. This is not good news for rainfall for spring and the first part of summer for the Summer Rainfall Area. Forecasts however showing a weakening towards November.
3. Expected rainfall and temperature conditions
3.1 Summer Rainfall Areas
3.1.1. Rainfall
With the development of a positive IOD (Indian Ocean Dipole) for the next months can it have a negative effect on the probabilities for rain in spring and early summer. The outlook that favours a more neutral state of ENSO can favour mid to late summer. It seems that a summer pattern starts to develop with rainfall shifting from the winter rainfall areas towards the east coast areas and adjacent interior. Sufficient rain to plant is not expected before the second part of October over the eastern summer production areas and not before the first part of November for the central to western parts. The extreme drought stricken areas in the Northern Cape and northwest Province will most probably only receive after the end of November any rain.
3.2 Winter Rainfall Areas
With the El Nino now starting to weaken, can it also negatively impact on rainfall for the Western Cape, especially towards the Swartland and West coast in the next weeks. This can negatively impact on the winter grain crop and may result in some drought damage to start to occur.
3.3 Namibia
It is likely that very little rain will occur for the next months and with a possible late start of the summer rainfall season of 2019/20.
4. Summary and conclusions
The redevelopment of El Nino is becoming less likely with more neutral conditions the highest probability to occur. This can have positive effects on mid- to late summer rainfall.
Rainfall conditions for the Winter Rainfall Region for the rest of August and September less favourable compared to previous forecasts. This is especially true for the Swartland and West coast.
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