Seasonal Climate Watch
February to June 2017
Date: January 23, 2017
1. Advisory
Most of the local and international forecasting systems consistently indicate that South
Africa’s summer-rainfall areas may expect wetter conditions during the latter parts of the
summer season (FMA). The likelihood, slightly favouring wetter conditions, however
remains relatively low. Temperatures are expected to be warmer than normal across the
country, though similar to the rainfall outlook there is a significant amount of uncertainty
in the forecast.
2. Recommendation
Even though some relief of the severe drought conditions has occurred over the eastern and
north eastern parts of the country the central and western parts of the country are still
burdened with below normal rainfall conditions. The public is reminded that with winter
on the horizon significant water loss can be expected with the usual decline of rainfall as
well as high amounts of evaporation, particularly over the summer rainfall areas. Thus
water saving measures to continue are highly recommended across the country. As usual,
it is also very important to keep monitoring any developments that may provide more
clarity on the current expectations for the coming seasons.
3. State of Climate Drivers
Observations show that ENSO (El Niño Southern Oscillation) has moved into a neutral
phase from the previous weak La Niña state. Upper-air wind patterns also indicate that the
usual La Niña state influence is marginal. The current neutral ENSO state may cast
substantial uncertainty on the prediction of rainfall and temperature conditions in our region
as noted above.
The Indian Ocean Dipole (IOD) is still in a neutral phase and it is expected to persist as
such for the coming seasons. The current trend of the Indian Ocean temperatures suggests
the formation of a positive dipole in the south-west Indian Ocean, which may enhance
moisture transfer towards the country in the latter parts of summer.
The Southern Annular Mode (SAM) has been showing a tendency for a negative phase
since November. The negative phase of the SAM and the weakening of the polar vortex are
often associated with colder and wetter conditions over the winter-rainfall region of South
Africa, through frontal activities. In spite of these frontal activities being more noticeable
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during the winter season, they have also positively contributed towards the current wetter
summer rainfall season.
4. Climate Forecast Details
4.1 Rainfall
The forecasting system shows chances for above-normal rainfall conditions for most of the
country the coming season, but with a relatively low probability (see Figure 1). It is worth
noting however that even though wetter conditions are expected throughout the autumn
season, the climatological rainfall tends to dramatically decrease over the north-eastern
parts of the country during autumn.
Figure 1: Rainfall forecasts for the three overlapping seasons valid for the period of February
to June 2017 and extreme forecasts for February to April 2017 season (right panel). Forecast
quality for total seasonal rainfall is indicated in the Appendix (Figure A1).
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4.2 Minimum and Maximum Temperatures
Forecasts show a tendency of above-normal temperatures with an increasing uncertainty
(see Figure 2). Similar to the rainfall noted above climatological temperatures drop towards
winter across the country and the expected conditions should be used accordingly.
Figure 2: Probabilistic minimum (left panel) and maximum (right panel) temperature
forecasts for the three overlapping seasons valid for the period of February to June 2017.
Forecast quality for average seasonal temperature is indicated in the Appendix (Figure
A2).
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Contributing Institutions
All the forecasts are a result of an objective multi-model prediction system developed at the
South African Weather Service. This system consist of long-range forecasts produced by the
following institutions:
Appendix
Figure A1: The skill of the forecasting system in discriminating wet or dry events during the
forecasting period as shown in the caption of each plot. Those regions with no shades imply
that the forecasts are not better than chance.
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Figure A2: The skill of the forecasting system in discriminating hot or cold events during the
forecasting period as shown in the caption of each plot. Those regions with no shades imply
that the forecasts are not better than chance.
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Tele: +27 12 367 6008