Important Issues- South Africa -First tropical cyclone in the Western Indian Ocean as well as first real El Nino development is negative for the short term as well as second part of the summer season respectively.
There is still however a possibility for good falls of rain from about the last week of November and parts of December and January.
1. Current conditions
Very little rain with temperature extremes occurred since the second part of October over much of the country. Minimum temperatures below 5°C in the interior with some areas even reported frost and snow occurred in the first week of November. This hampered the planting of summer crops in the eastern summer crop areas where the optimum planting window is nearing its end. For example are the last acceptable dates for soya beans to emerge in order to qualify for multi-peril crop insurance in the cooler Eastern Free State in districts like Bethlehem, Harrismith and Frankfort, about 15 November and in areas like Mpumalanga before the end of November. For maize to qualify for multi-peril crop insurance is the last date to emerge about the end of November for the eastern Free State and Mpumalanga (for shorter season growers is the acceptable date to emerge about a week to 10 days later). There are still large areas to be planted, especially in the east and north eastern Free State and parts of the area around Standerton, Bethal and Heidelberg in Mpumalanga. Very little or no plantings were possible in the central to western parts but the normal planting dates only commence from about the second part of November until the middle to last part of December.
Very little rain occurred over most of the Western and Eastern Cape in the last 2 to 3 weeks but very strong winds from a southern to south eastern direction increased the fire risk and fires with disastrous results occurred in some areas.
2. El Nino and Indian Ocean
Sea surface temperatures in the Nino3.4 area for the first time this season exceeded the 0.5°C above average limit and can now be described as El Nino provided it maintains this for a while.
The Indian Ocean Dipole Index (IOD) also moved to the positive phase, meaning that warming of sea surface temperatures are more towards the western Indian Ocean or closer to the African continent. Forecasts however are showing a relative short lived period with low intensity of warming. This development can be responsible for the very early occurrence of tropical cyclones in the western Indian Ocean.
3. Expected rainfall and temperature conditions
3.1 Summer Rainfall Areas
Very little or no rain is expected over most of the country until at least 23 November 2018, mostly as a result of the negative effects of cyclone “Alcide” over the Indian Ocean. Short term forecasts are positive for rainfall to commence in the last week of November as well as December and parts of January with even heavy falls possible over the eastern areas like KZN and Mpumalanga. It must be remembered that the chances for rain decreased more towards the western parts of the country with lower probabilities for good rain. It seems that a drier scenario is now more possible over the western parts compared to initial forecasts with negative short term forecasts and a negative forecast due to the expected effects of El Nino later in the season.
A positive aspect is that the current developing El Nino not yet interacted with weather systems and that the neutral status up until now still the weather systems can dominate with improved rainfall conditions compared to pure El Nino conditions. The presence of tropical cyclones like “Alcide” can however suppressed the possibility for rain over the short term.
3.2 Winter Rainfall Areas
Very little or no rain is expected for at least the next two to three weeks over the western parts of the Western Cape but light falls of rain is possible over the Southern and Eastern Cape coastal areas from about 20 November.
3.3 Namibia
Although improved rainfall conditions is possible from about the last week in November, is the rest of the season less favourable. The expected negative effect of El Nino in the second part of the season can result in challenging agricultural conditions.
4. Summary and conclusions
Although El Nino only now shows signs of development will the possible negative effect only be later in the season. Short term forecasts up until about 23 November are negative for rain.
The chances for rain improved from about 23 November and parts of December and even January BUT it is likely to be restricted to the central and eastern parts. The central to western parts are at risk for below average rainfall conditions with consequent poor grazing conditions to continue.
Very little rain is expected over the western parts of the Western Cape but light falls are possible over the Southern and Eastern Cape in the last week of November.
SANTAM Johan vd Berg
