After large parts of South Africa experienced a drought in January, the central parts of the country are expected to receive wide-spread thundershowers over the weekend, especially the Free State and Northwest.

The next few days will be a bit hotter while thundershowers may occur towards the weekend over the eastern and north eastern parts of the country.

Conditions over the interior, including the entire maize-production region, will remain favourable for rainfall during the next few days.

The summer rainfall region can expect more widespread thundershowers after an extended hot spell. The winter rainfall region will remain mostly dry.
 
Wetter conditions following heat and drought
After more than a week of hot and dry conditions, a much more favourable situation is now becoming established. Fairly widespread thundershowers will occur during the next few days over the summer rainfall region, excluding the western parts. Some thundershowers may become severe. This is the result of the typical unstable conditions related to upper-air dynamics and surface air interactions that usually occur in early summer.

The early maize-production region over the northern Free State and Mpumalanga will especially benefit from the developing conditions and thundershowers will occur on most days over these areas. This is very good news for especially the northeastern parts of the Free State and southwestern Mpumalanga. Here, most of the region should receive above-normal rainfall.

The southern parts of the country will be cool due to an on-shore flow for most of the time, while some showers are expected especially along the Garden Route towards the west (Tuesday, 20th) and east (Wednesday, 21st). The winter rainfall region is expected to remain dry during the period except for some initial showers by the 20th.

While cool to cold air will initially invade the country, especially the western to central parts, it will become hot over the western interior from the 23rd (Friday).

The following is a summary of weather conditions during the next few days:

Normal to above-normal rainfall is expected over the eastern to northeastern summer rainfall region during the next few days, with some thundershowers also possible at times over the central parts.

The western interior (mostly Northern Cape) will remain dry during the next few days.
Cool, dry air will spread over much of the western, southern and central interior during Tuesday (20th) and Wednesday (21st).
Minimum temperatures over the central to southern interior will be relatively low on Wednesday (21st) and Thursday (22nd) morning.
It will be significantly colder (+/- 10° C drop in temperatures) over the southern interior (most of the Western Cape and Eastern Cape) on Tuesday and Wednesday (20th and 21st), accompanied by strong southerly to westerly winds. The wind should be especially strong along the coast.

Small areas of frost may occur over the southern escarpment on Wednesday and Thursday morning.
Thundershowers will occur over most of the northeastern parts on Tuesday (20th). Some of these may become severe, with strong winds and hail possible in places especially during the late afternoon.
Rain and showers will occur from the western winter rainfall region and western Garden Route (Tuesday 20th) moving through to the eastern Garden Route (Wednesday 21st) before clearing.
Most of the country will be dry on Thursday (22nd).
Thundershowers will redevelop over the northeastern parts from Friday. Scattered thundershowers should occur from the Free State and North West eastwards during the weekend. These should continue into early next week.
Some thundershowers during the weekend and early next week will become severe, including parts of the Free State and North West.
There are early indications of more significant rainfall over the summer rainfall region by Tuesday (27th) with rain also indicated over the southern coastal belt and adjacent interior. These projections specifically are somewhat far ahead of time and not necessarily considered reliable.
It will become hot and dry over the western interior from Friday (23rd).
Strong southeasterlies are expected over the southwestern coastal areas most of the time. Where vegetation is dry, this could enhance the probabilities for the development and spread of wild fires.

Seasonal overview
The tropical Pacific continues to meet some, but not all, El Niño criteria. The Bureau's ENSO Outlook remains at El Niño ALERT, meaning there is at least a 70% chance of El Niño fully forming in 2018.

Sea surface temperatures in the tropical Pacific Ocean now exceed El Niño thresholds. However, atmospheric indicators - such as trade winds, cloudiness, pressure patterns and the Southern Oscillation Index (SOI) - have yet to show consistent or sustained signs of El Niño. This clearly indicates that the tropical ocean and atmosphere are not currently reinforcing each other and remain 'uncoupled'. This coupling is required to not only fully develop and sustain an El Niño, but is what drives widespread global weather and climate impacts.

International climate models predict sea surface temperatures to remain above El Niño levels in the coming months. By February, two of the eight surveyed models dip just below El Niño thresholds.... - Australian Bureau of Meteorology - http://www.bom.gov.au

The Southern Oscillation Index has been trending negative since early this year, an indication of a negative atmospheric response to warmer SSTs, signalling a trend towards El Niño-like conditions. Australian Bureau of Meteorology - http://www.bom.gov.au

Based on the developing El Niño, forecast models lean towards a tendency for drier conditions by late summer, while early to mid-summer is expected to be relatively wet over much of the interior. Coupled with the dry signal towards late summer, there is also a concomitant indication of warmer than usual conditions. The positive temperature anomalies are also indicated for early-to mid-summer.

It is worth noting that, while seasonal forecasts tend to indicate drier conditions towards late summer, this is a weaker signal than what is sometimes associated with El Niño summers, possibly at least in part due to the weakness of the event. The following are the latest seasonal forecasts for Africa, from the IRI, for mid (December - February) and late (January - March) summer respectively.

There are indications that the summer rainfall region may experience above-normal rainfall during early to mid-summer with a very slight indication of possible warmer-than-normal conditions (Forecasts by the IRI - http://iri.columbia.edu/).

Towards late summer, seasonal forecast models suggest somewhat drier-than-normal conditions over much of the interior, with a stronger indication of the development of a warm anomaly, centred towards the northwest of South Africa (Forecasts by the IRI 

Expected rainy season progression, associated with decadal variability (issued 22 October 2018)

Since summer 2017/18, in terms of decadal climate forcing, there has been a push towards El Niño conditions. Global Climate Models therefore predict the onset of El Niño conditions during the next few months. The negative forcing experienced during the last few months, giving rise to the development of weak El Niño conditions, will be replaced by a positive influence on the climate system during the next few months.

By late summer, there should be a strong push towards La Niña conditions - this may result in wetter than normal conditions over large parts of the summer rainfall region by late summer. Conditions therefore, during most similar summers as 2018/19, are usually somewhat drier in early to mid-summer, but wetter towards late summer. This is somewhat different to the typical El Niño signal as is forecast by climate models. Given the El Niño-like conditions present currently, it may be safe to assume a tendency towards drier conditions with above-normal temperatures during large parts of the summer. However, based on conditions in similar years in the past, the January-March period may turn out quite favourable.

The early rain experienced over the summer rainfall region since late September should largely be replaced by relatively dry conditions into November. This may likely be interspersed by a short wet period in early November. From late November, there is likely to be a resurgence of relatively wet conditions over the summer rainfall region, possibly lasting into December. Again, by late December/early January, it may once again be drier - basically during the period when the mid-summer drought usually occurs. If this dry period develops, it will most likely not be as severe as during 2017/18. From late January, conditions may very well improve again, and then even more so from early February. Based on the tendency in previous similar years, there is a possibility that large parts of the summer rainfall region could receive above-normal rainfall during February and/or March, while globally the indicators should start signaling the possibility of a La Niña towards 2019/20. Should the wet conditions develop in the north, there is also an enhanced likelihood of tropical systems (such as tropical depressions/storms/cyclones) influencing the region.

Normal to above-normal rainfall is more likely to occur over the eastern parts of the summer rainfall region during early to mid-summer (top, OND - October, November, December), while the west is likely to remain drier than normal. Towards late summer (above, JFM - January, February, March), there is a strong indication that above-normal rainfall may develop over the northeastern parts of the country, spilling also into the central parts. The western parts will still be more likely to receive below-normal rainfall.

Seasonal outlook: Summary
Based on the current state of El Niño, it is safe to assume that there will 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 suggest a very weak negative influence. The only difference here is that the predictions based on decadal variability suggest increasing wetness towards the end of the summer, with a drier start, while Global Climate Models suggest wetter conditions earlier, drying somewhat towards late summer.
Rainfall (% of long-term mean): October 2018

Parts of the Eastern Highveld, the northern coastal belt of KZN and southeastern Northern Cape received above-normal rainfall during October. The rest of the country was mostly drier than normal.

Vegetation activity is above normal over the northern to eastern parts of the eastern maize-production areas due to a normal start to the rainy season over much of the area. However, the northern parts of the Free State and southwestern parts of Mpumalanga experience drought stress and need rain soon. The projected rainfall from the weekend onwards may favour these areas. Over the winter rainfall region, grain-production areas are also still experiencing above-normal vegetation activity following a normal to above-normal rainy season. There are still indications of drought stress over the northern parts of the West Coast, extending into the Great and Little Karoo and the western parts of the garden Route. A slow start to the rainy season is noted over much of Limpopo, where vegetation activity is also below normal. Another area where some drought stress is noticeable is the eastern parts of the Northern Cape and northwestern Free State extending into much of central North West.

Overview of expected conditions over South Africa during the next few days
Upper-air troughs and perturbations moving across the interior, together with the Atlantic Ocean Anticyclone ridging strongly around the country on two occasions, will result in a much more favourable situation over the summer rainfall region for rain compared to the last few weeks.

The first upper-air trough will move across the interior on Tuesday (20th), and out eastwards by Wednesday (21st). At the surface, an influx of cool, dry air will result in clearance from the west, after initial rainfall over the winter rainfall region. The influx of cooler air will be felt over the southern parts with some showers and windy, cold conditions on Tuesday (20th) and Wednesday (21st). The invading dry air may also result in a tendency for severe storm development where scattered thundershowers occur over the summer rainfall region.

It will be dry over most parts on Wednesday and possibly Thursday (22nd), but upper-air perturbations moving into the central to northern parts and a renewed influx of moisture as an anticyclonic circulation pattern strengthens to the east of the country will result in a renewed development of thundershowers over the northeastern to central parts from Friday. Interaction between moisture and dry air, together with upper-air dynamics, may result in some thundershowers becoming severe.

During early next week, an approaching upper-air trough and renewed ridging of the Atlantic Ocean Anticyclone, may result in more significant and widespread rainfall over the interior - given the long lead time, this outlook is still uncertain.

Conditions in main agricultural production regions (20 - 26 November)
Maize production region: Scattered thundershowers will occur over the region on Tuesday (20th). Some of these may become severe. It will be dry on Wednesday over most parts. From Thursday, scattered thundershowers will occur, continuing through the weekend. There may be an improved distribution of thundershowers over the western parts compared to earlier in the period. Temperatures will on average be in the normal ranges.

Cape Wine Lands and Ruens: Following some showers initially (Tuesday 20th), it will become fine and mild for the most part. It will be warm over the West Coast, Swartland and Karoo from Thursday (22nd) to Saturday (24th). Winds along the southwestern coastal areas will be strong southeasterly most of the time.

According to current model projections (GFS and CCAM atmospheric models) of weather conditions during the coming week, the following may be deduced:

Thundershowers over the central to northeastern parts may become severe on Tuesday (20th).
A sharp drop in temperatures on Tuesday (20th) with strong winds and rain during the night may affect small stock negatively over the southern to southeastern interior (up to the southern escarpment over the Western Cape and Eastern Cape).
Thundershowers over the central to northeastern parts during the weekend and early next week may again become severe with strong winds and hail possible.
Strong southwesterly winds are possible along the southeastern coastal areas (mostly Eastern Cape) by Tuesday (20th).
It will be very hot over the Lowveld and most of the Limpopo River Valley on Tuesday (20th) and Wednesday (21st).
Strong southeasterlies are possible over the southwestern coastal areas on most days. Where vegetation is dry, this may be conducive to the development and spread of wild fires.
Hot conditions will develop over the Northern Cape from Friday (23rd) to Sunday (25th).
There is a possibility of significant rainfall over the eastern to southeastern parts by Tuesday (27th). Given the long lead time, this forecast is still very uncertain.
Sources

Agricultural Research Council - Institute for Soil, Climate and Water (ISCW) - Climate Data Bank. Data recorded by the automatic weather station network of the ARC-ISCW.

Thundershowers over the central parts on Friday may become severe with strong winds and a possibility of hail. Strong southeasterlies are expected over the southwestern coastal areas.

The conditions will become more favourable for summer rainfall over the northeastern half of the country. Meanwhile sea surface temperatures in the tropical Pacific Ocean have exceeded El Niño thresholds for more than a month.

Once again wetter than average conditions are expected to continue over large parts, including the maize-production region. 

Following a week of widespread rain and persistent cloudy conditions over much of the summer rainfall region, the next few days will bring a situation more typical of normal summer conditions with isolated to scattered thundershowers and abundant sunshine.

More widespread rain and thundershowers are expected over the summer rainfall region during the next few days.

The next few days are expected to be somewhat cooler than the norm for this time of the year over the southern to eastern parts of the country, where easterly to south easterly winds will advect moisture for most of the days with substantial cloud cover at times.

Warm and dry conditions will persist over the north western parts (mainly northern half of the Northern Cape and adjacent areas) according to current forecasts. The generally favourable rainfall situation over the interior will also be associated with strong south easterlies in the southwest. Rain-bearing systems (cut-off lows) over the southern parts may also be associated with heavy downpours at times and possible severe storms in places.

The following is a summary of weather conditions during the next few days:

• General:
o The period will be relatively cool over the southern to eastern parts with above-normal rainfall.
o The winter rainfall region is also expected to receive rain
o The northern half of the Northern Cape and adjacent areas are expected to remain mostly dry. o It will be very windy over the southern parts of the country at times.
o It will generally be windy for this time of the year over most of the interior, especially the central to southern parts and from time to time also over the Highveld.
o Strong south easterlies are possible over the southwestern parts for most of the period.

• Rainfall:
o Scattered showers and thundershowers are expected on most days over the central to eastern summer rainfall region, including the entire maize-production region except for the extreme southwestern parts.
o Widespread rain and thundershowers are possible over Limpopo and central to eastern Mpumalanga during the weekend. Heavy falls are possible along the escarpment and the Lowveld.
o Scattered rain and thundershowers are expected over the Western Cape, Eastern Cape and southern parts of the Northern Cape during the weekend and possibly again by Wednesday (22nd). Heavy falls are possible over the mountainous areas in the Western Cape.
o Except for isolated thundershowers at times, the northern half of the Northern Cape should remain dry for the most part according to current forecasts.

• Temperatures:

o It will be cool to cold over the southern parts, with maximum temperatures below 20°C, accompanied by strong winds which should lower the sensible temperature, during the weekend and into early next week as well as possibly by Wednesday and Thursday (22nd and 23rd).
o Mild conditions will dominate over the interior and along the coast for the most part. Maximum temperatures over the interior will remain below the lower 30s for the most part.

Overview of expected conditions over South Africa during the next few days

A tropical low-pressure system in the north, moving across Zimbabwe, together with an upper-air low over Botswana will initially bring widespread rain and thundershowers to the north eastern parts. Two upper-air cut-off lows developing over the southwestern parts during the period will also result in widespread thundershowers over the interior, together with rain and thundershowers over the southern parts, including the winter rainfall region. Conditions in main agricultural production regions (17 - 22 January)

Maize production region:

It will be cooler than normal for most of the period. Isolated to scattered showers and thundershowers are expected on most days. Maximum temperatures over the western maize-production region will range between 24 and 30 °C. Minimums will be in the order of 14 - 19°C. Maximum temperatures over the eastern maize production region will range between 22 and 29°C while minimums will be in the order of 10 - 15°C.

Cape Wine Lands and Ruens:

Widespread rain and thundershowers are expected, especially during the weekend and again by Wednesday (22nd). The wind will be strong southerly to south easterly, especially in the southwest, especially during the weekend and again by the 22nd. Temperatures will be below normal for this time of the year.

Possible extreme conditions - relevant to agriculture

According to current model projections (GFS model) of weather conditions during the coming week, the following may be deduced:
• Rain and thundershowers over the north eastern parts may result in heavy falls over the north eastern escarpment and Lowveld during the weekend.
• Showers or thundershowers during the weekend over the mountainous regions of the Western Cape may be associated with heavy downpours and could possibly lead to localised flooding.
• Thundershowers during the weekend and next week over the mountainous regions of the Western Cape may have a tendency to become severe, with hail.
• Cool, wet and windy conditions over the southern parts of the country for extended periods may have a negative impact on small stock.
• Some thundershowers over the central parts of the country by next week may have a tendency to become severe.

Following a cloudy, rainy spell during the weekend and early this week, the next few days will be mostly sunny and dry, with current indications of the first widespread wetter conditions only by next week.

Pleasant autumn weather is set to continue over most areas, but conditions will be more favorable for rainfall over parts of the interior compared to the previous week.

The next few days will see a continuation of the rainy conditions over the central parts of the country, intensifying somewhat during the remainder of the week and moving eastwards to be confined to the eastern and northeastern parts by Saturday (4th).

Relatively favorable conditions for isolated to scattered thundershowers will be present over the central parts of the country initially, remaining in place until the weekend.

Summary Wet weather remains in place over summer grain-production areas Widespread rain continued over much of the central to northeastern parts of the country during the last few days, with persistent wet conditions leading to increasing levels of rivers ad dams in many areas.

The following is a summary of weather conditions during the next few days:

Summary Wetter conditions return to the summer rainfall region Following a mostly dry April, conditions are expected to return to a wetter pattern into early May.

A number of rain-producing systems moved across the country during the last few days, but rainfall was less extensive and totals generally lower than during the preceding weeks.