Summary
La Nina remains at moderate levels but is already well established. The Indian Ocean is in a strong negative phase of the Indian Ocean Dipole. Both developments are positive for rain in midsummer for the Summer Rainfall Area.
Rainfall conditions for the Winter Rainfall is improving for “out of season” rainfall in November when the harvesting of winter wheat will be in full swing.
There is a very high risk for hail and strong winds.
A high risk also for the spread of veld fires for the western and northern interior.
Current conditions
Very hot conditions occurred over large parts of the Summer Rainfall Area since the end of September. Maximum temperatures of up to 40°C or higher were measured in die central to north-western parts of the country. This was associated with dry conditions, but isolated thunder showers started to occur. There was also rain associated with lightning in parts of the Western Cape. Light hail also occurred in the Hexriver Valley that is very unusual. A hailstorm also hit the southern parts of Guateng. Rainfall since the start of October were very patchy but more scattered showers occurred in the third week of October that will allow farmers to start planting summer crops.
Very little plantings of summer crops were possible up until the middle of October due to dry upper layers of soils. Deeper layers of most soils are still wet to very wet as a result of the above average rainfall in the second part of the 2021/22 summer season. Farmers only need about 20mm to 30mm to plant and with more than 50mm it could again result in too wet conditions.
The harvesting process of winter grain crops started in the Winter Rainfall Areas. Although below average rainfall was recorded in most of the production areas, was the distribution over time more favourable with regular rainfall events associated with cool and cloudy conditions, restricting drought damage to a certain extent.
The fire season in the western interior is entering probably the most dangerous part with lightning strikes able to start veldfires and stormy conditions and strong winds fuelling the spread. Grazing conditions are in general favourable for this time of the year and with careful managing fire damaged areas, is recovery expected to be fast due to favourable soil moisture conditions and well-developed rooting systems.
Storage dams in the Summer Rainfall Area are still at very high levels with Free State dams at 94% of full capacity compared to about 90% the same time last year. The Vaal dam is still at 91% (82% last year), Bloemhof dam at 89%, Vanderkloof dam at 96% and Gariep dam at 94%. With expected average to above average rainfall in coming months is it expected that storage dams will fill up rapidly to be at full capacity before the end of 2022. Western Cape dams are on average 72% of full capacity with rapidly falling levels (Last year this time it was 81% of capacity). The Theewaterskloof dam is currently at about 81% compared to 100% last year the same time and the Clanwilliam dam at 85% compared to 99% last year. The level of the Clanwilliam dam is of concern because if it is not 100% full at the start of the summer season, water restrictions are possible later in the summer season. Eastern Cape dams are on average 73%, compared to last year with 51%. The important Kouga dam improved to about 22% compared to 6.6% last year the same time. The Impofu dam is at 9.6% compared to 17.1% last year.
The water level in Lake Kariba in Zambia is at about 13% of the useable storage compared to 35% last year the same time and there is reason for serious concern for the ability to sustain hydropower generation. The Katse dam in Lesotho is at 84.7% and the Mohale dam at 88.9%. The Hardap dam in southern Namibia is at 57% of full volume while the largest storage dam, the Neckartal dam is at 96.4%.
2. ENSO and Indian Ocean
2.1 ENSO (El Nino Southern Oscillation)
Nearly all Nino-areas intensified towards cooler conditions since August 2022 and some of the Nino-areas like Nino-4 (closest to Australia) and Nino-1+2 (closest to the Americas) are currently cooler than last year the same time with other Nino-areas at about the same level. The 2022/23 La Nina is expected to reach about the same intensity as in 2021/22 in midsummer but forecasts indicate a weakening trend from about the turn of the calendar year (December/January) compared to the La Nina event in 2021/22 that intensified from about February to June 2022.
2.2 Indian Ocean
The Indian Ocean Dipole Index (IOD) is in a strong negative phase and index values will be about 1°C cooler than normal until the end of October before it will weaken to become also neutral in about November/December.
The current negative phase of the IOD index is the strongest since at least 2018 and is significantly positive for rainfall.
3. Rainfall and Climate Outlooks
3.1 Summer Rainfall Area
The current La Nina is well established, although at moderate levels as was the case in 2021/22. With the positive signal from the Indian Ocean are the following the outlooks possible for the season:
3.1.1 Limpopo, north Gauteng, northern interior of KZN and Lowveld:
· Long term: Below average rainfall until about November for the western parts but average to above average rainfall for the central to eastern parts from November up to February. Probable drier conditions in the second part of summer from February to May.
· Short term: Very little or no rain until at least the end of October for the central to western parts but good falls up to 50mm possible over the eastern parts until the end of October. There is a high risk for hail and stormy conditions. Hot to very hot conditions can be expected over the western and northern parts but cooler towards the east.
3.1.2 Southern Gauteng, Highveld of Mpumalanga, and north-eastern Free State:
· Long term: Below average rainfall until the end of October but average to above average from November to January. Drier spell from about February.
· Short term: More than 30mm to 50mm expected until the end of October. There is a very high risk for hail and storms associated with rain.
3.1.3 Northern Cape (north of Orange River), Northwest Province and central/western Free State:
· Long term: Below average rainfall until the middle of November but average to above average from December to February. Drier spell from the end of February.
· Short term: Only isolated falls of rain until at least the end of October. High risk for hail and strong winds. The risk for veld fires is also peaking now with lightning igniting the above average amount of combustible material. Hot to very hot for the rest of October and first part of November
3.1.4 Eastern Free State, southern parts of KZN and northern parts of the Eastern Cape:
· Long term: Rainfall conditions are improving towards November but average to above average from November to January. Dry in the second part of summer.
· Short term: More than 50mm is expected for the rest of October and first part of November. High risk for hail and strong winds. Very cloudy conditions.
3.1.5 Southern parts of the Northern Cape and adjacent areas of the Eastern Cape
· Long term: Below average rainfall conditions until about the end of November. Average to above average rainfall from about December.
· Short term: Very little or no rain except for isolated light falls in the first week of November. Warmer temperatures are expected.
3.1.6 Coastal areas of the Eastern Cape as well as rest of Garden Route
· Long term: There is a high probability for rain in the first part of summer, especially until about December. Heavy rain is possible with possible flood conditions.
· Short term: Rain of up to 50mm is possible for the northern parts of the Eastern Cape coastal areas with less rain more towards the South Coast. Cool to moderate for the rest of October and November with a high cloud load.
3.1.7 KZN interior and northern coastal areas
· Long term: Average to above average rainfall from the last part of October until December.
· Short term: Up to 50mm or more rain is possible in the next two to three weeks. Localised flooding possible.
3.2 Winter Rainfall Area
· Long term: There is an increased probability for rain in November and December due to La Nina development, allowing tropical moisture to flow south and south-east over the southern interior into the Winter Rainfall Region.
· Short term: Light falls and very cloudy conditions possible towards the end of October but heavier rain of more than 20mm possible in the first two weeks of November. This can have serious consequences on quality of winter wheat with the harvesting process to be in full swing during this time.
3.3 Namibia
Very little or no rain is expected until at least the middle part of November but average to above average rainfall from December to February. Temperatures will be warm to hot.
