Isolated thundershowers are possible on Friday (17th) over the southern to western Free State and the Eastern Cape. Towards early next week, a significant cold front may invade the winter rainfall region. Except for some showers today (Tuesday, 14th), very little rain is expected over the winter rainfall region until Sunday (19th). Traditionally, the last few days of May bring somewhat more inclement conditions to the interior. The chance for wetter and colder weather over the interior therefore escalate from next week onwards (based on conditions in the past).
The following is a summary of weather conditions during the next few days:
• General:
o Little to no rain is expected over the country.
o The winter rainfall region should remain relatively dry until Sunday (19th).
o Temperatures over the interior will on average remain normal to above normal, with largest positive deviations over the central to western interior.
o The interior, including the maize-production areas, will continue to warm up slightly during the period.
o There is no indication of severe frost given the expected weather conditions during the next few days.
o Fresh to strong northwesterlies will occur over the southwestern parts from Sunday.
o Dry, warm and windy conditions will result in a relatively high fire danger over the interior, especially the northwestern and central parts, on most days.
• Rainfall:
o Most days will be sunny and dry over the interior.
o Light showers are possible over the winter rainfall region (especially southern parts) and Garden Route (especially western parts) on Tuesday (14th).
o Isolated thundershowers are possible over the southern to western Free State, extreme eastern parts of the Northern Cape, Eastern Cape as well as southern KZN on Friday.
o Isolated showers are possible along the eastern to northeastern escarpment on Saturday (18th).
o Widespread rain and showers are possible over the winter rainfall region on Monday (20th).
• Temperatures:
o Hot, berg-wind conditions are still possible over the southern to western interior and Tuesday (14th).
o It will remain warm to hot over the western to northwestern interior throughout most of the period with northerly to northwesterly winds.
o Pre-frontal conditions will lead to warm, windy weather over most of the interior by Sunday (19th) and Monday (20th).
o Hot, berg-wind conditions may occur over the Eastern Cape, KZN and Lowveld on Sunday (19th) and Monday (20th).
o Maximum temperatures over the western maize-production region will range between 25 and 30 °C while minimums will be in the order of 3 – 12°
o Maximum temperatures over the eastern maize-production region will range between 23 and 28°C while minimums will be in the order of 2 – 10°C.
Seasonal overview
El Niño and seasonal forecasts
According to the Australian Bureau of Meteorology the chances for the strengthening of El Niño during the next few months are diminishing while according the International Research Institute for Climate and Society, there remains a reasonable likelihood of an El Niño during 2019. In general, both these outlooks are less optimistic for the strengthening of a warm event and expect a short-lived event:
ENSO (Updated 14 May): Indicators have been close to El Niño thresholds over the past several months, but signs have emerged of a weakening of these patterns. As a result, the Bureau's ENSO Outlook has been downgraded to El Niño WATCH. This means the chance of El Niño developing in 2019 is approximately 50%, which is still double the normal likelihood.
While sea surface temperatures in the tropical Pacific Ocean remain close to El Niño levels, water beneath the surface has slowly cooled over the past few months. Atmospheric indicators such as the Southern Oscillation Index (SOI) and cloudiness near the Date Line have generally remained in the neutral range, despite short-term El Niño-like SOI values in the last fortnight.
Seasonal outlook: Summary
Based on the state of El Niño, it was safe, by mid-summer, to assume that there would be a tendency towards drier and warmer conditions at least in part during the summer. However, both Global Coupled Models and forecasts based on the decadal variability in the climate system suggested a weak negative influence. The only difference was that the predictions based on decadal variability (issued here) suggested increasing wetness towards the end of the summer, with a drier start, while Global Climate Models suggested wetter conditions earlier, drying somewhat towards late summer. In terms of forecasting wetter conditions towards late summer with drier conditions earlier, the forecast issued in the Cumulus was more accurate than other forecasts.
Overview of expected conditions over South Africa during the next few days
Anticyclonic conditions will dominate over the interior for most of the period. Isolated thundershowers are possible over the southeastern parts as an upper-air trough moves through on Friday (17th). A cold front will make landfall in the southwest on Monday. This may result in stormy weather over the winter rainfall region.
Conditions in main agricultural production regions (14 - 20 May)
Maize production region: Sunny and mild to warm conditions will prevail for the most part with little to no indication of frost. On average, temperatures over the western parts will be 3 – 7 °C above the long-term mean, while the eastern parts will be 2 – 5°C warmer than the norm. Maximum temperatures over the western maize-production region will range between 25 and 30 °C while minimums will be in the order of 3 – 12°. Maximum temperatures over the eastern maize-production region will range between 23 and 28°C while minimums will be in the order of 2 – 10°C.
Cape Wine Lands and Ruens: Rainfall during this period is expected to remain below normal over the region until the weekend. A frontal system may bring widespread rain early next week. A frontal system may bring light showers and fresh westerly winds to the region on Wednesday (8th). It will become warm to hot along the West Coast from Friday (10th) onwards. Strong south-easterly winds are possible in the southwest on Sunday (12th) and Monday (13th).During this time, light showers are possible along the Garden Route.
According to current model projections (GFS and CCAM atmospheric models) of weather conditions during the coming week, the following may be deduced:
• Strong northwesterly winds are possible over the southwestern parts on Sunday (19th) and Monday (20th).
• Strong northwesterly winds and high temperatures are possible over the Northern Cape interior on Friday (17th) and over the central to southern and southeastern parts of the country, including the Northern Cape interior, by Sunday (19th) and Monday (20th). Where vegetation is dry, these may be conducive to the development and spread of wild fires.
• Cold, wet and windy conditions may set in over southwestern parts of the country on Monday (20th) according to current forecasts. These may impact negatively on small stock.
