Summary
La Nina remains at weak to moderate levels but is already well established. The Indian Ocean is in a strong negative phase of the Indian Ocean Dipole.
The combined effect of the La Nina and Indian Ocean developments are both very positive for summer rain from about October/November over the eastern parts and November/December over the central to western parts
Rainfall conditions for the Winter Rainfall Area improved over the short term with light falls possible, especially 7 to 11 October where up to 20mm is possible. Possible rain in November with strong summer systems due to La Nina and Indian Ocean.
The probability for extreme cold events and frost is rapidly decreasing.
1.Current conditions
Rainfall totals in the Winter Rainfall Area is still below average but regular light falls due to weak cold fronts were able to prevent serious drought damage to the winter grain crop. Malmesbury received a total of 61.6mm since the 1 August compared to a long-term average of about 95mm, Hopefield 46.8mm compared to about 80mm long-term and Bredasdorp 43.8mm with a long-term average of 92mm. There were between 15 and 20 days with rain, indicating the very low amounts of rain per day but a higher frequency with rain every third to fourth day. Rainfall conditions in the next weeks will determine the final crop.
Winter grain conditions in the Summer Rainfall Area are favourable although there is still a frost risk, especially in the Lower Orange River areas. Minimum temperatures dropped the below 3°C on 21 September in some of these areas and damage is possible in lower lying areas.
Snow and very cold conditions occurred in the northern parts of the Eastern Cape and adjacent parts of KZN and the Free State in the last part of September. The first summer rainfall was recorded in the Eastern Cape, KZN and adjacent parts of Mpumalanga. Significant falls were measured from 11 to 20 September 2022 in KZN: Richardsbay 53mm, Margate 41mm and Greytown 24mm; Eastern Cape: Fort Beaufort 66mm, Port Alfred 51mm; Queenstown 50mm and Gqeberha 44mm; Mpumalanga: Mbombela 20mm and Emalahleni 17mm.
The fire season is now in progress with increased windy and hotter conditions. With rain still absent until at least the end of October, can the rest of September and October see a very high fire risk.
Storage dams in the Summer Rainfall Area are still at very high levels with Free State dams at 96.5% of full capacity compared to 90.5% the same time last year. The Vaal dam is still at 96.2%, Bloemhof dam at 96.9%, Vanderkloof dam at 98.6% and Gariep dam at 93.6%. Western Cape dams are on average 74.6% of full capacity towards end of September 2022 (Last year this time it was about 82% full). Eastern Cape dams are on average 69.5% compared to last year with 52.7%. The important Kouga dam improved to about 20% compared to 5.5% last year the same time. The Impofu dam is at 9.9% compared to 17% last year.
The water level in Lake Kariba in Zambia is at about 19.8% compared to 40% last year the same time while the Katse dam in Lesotho is at 86.7% and the Mohale dam at 94.3%. The Hardap dam in southern Namibia is at 59.9% of full volume while the largest storage dam, the Neckartal dam, at 97%.
2. ENSO and Indian Ocean
2.1 ENSO (El Nino Southern Oscillation)
The Nino-areas are nearly all about 0.8°C to 0.9°C cooler than normal, representing a weak to moderate La Nina. Although at weak levels, is it at stronger levels as the same time last year. It is also well established due to the fact that it is the third consecutive event.
It is expected that La Nina will remain at weak levels until about December/January when it will start to weaken to reach neutral values in about January/February.
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 in September and October before it will weaken to become also neutral in about 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
With strong positive rainfall signals from both the well-established weak to moderate La Nina and the negative phase of the IOD, are the following the most probable outcomes in terms of rainfall and temperature:
3.1.1 Limpopo, north Gauteng, northern parts of KZN and Lowveld:
Long term: Below average rainfall until about the end of October but average to above average rainfall from November to February. Probable drier conditions in the second part of summer from February to May. The frost risk is now very low.
Short term: Very little or no rain until at least the end of October for the central to western parts but rain is possible over the eastern parts and the Lowveld in the next weeks.
Temperature: Very hot conditions can be expected over the western parts from about 25 September and most of October.
3.1.2 Southern Gauteng, Highveld of Mpumalanga, and north-eastern Free State:
Long term: Below average rainfall until middle October but average to above average from November to January. Drier spell from about February. Frost risk now very low.
Short term: Very little or no rain until at least the middle of October.
Temperature: Hot to very hot conditions from about 25 September and most of October.
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. The probability for late frost is becoming low although there is a risk in October.
Short term: Very little or no rain until at least the end of October. No further frost is expected. Temperature: Very hot from the last part of September but especially 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 will start to improve in October but average to above average from the last part of October to January.
Short term: Up to 20mm is possible for the coastal areas until the first week of October. Less rain for the eastern Free State and north-western parts of the Eastern Cape.
Temperature: The probability for extreme cold conditions is lower for the next week or two.
3.1.5 Southern parts of the Northern Cape and adjacent areas of the Eastern Cape
Long term: Below average rainfall conditions until about October/November. Average to above average rainfall from about December.
Short term: Very little or no rain.
Temperature: 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 from about September but especially October with the migration of winter to summer rainfall conditions along the east coast. There is even a flood risk, especially the Eastern Cape coastal areas.
Short term: Rain of up to 20mm is possible for the next weeks, especially the northern parts of the Eastern Cape coastal areas.
Temperature: Cool to moderate but hot from about October.
3.1.7 KZN interior and northern coastal areas
Long term: Rain is possible over the coastal areas from about September and can migrate later into the northern interior.
Short term: Up to 20mm of rain is possible in the next two to three weeks.
3.2 Winter Rainfall Area
Long term: Average to below average rainfall for the rest of September and October but there is an increased probability for rain in November with the La Nina development.
Short term: Light falls of rain due to frontal activity, especially towards the Rûens and Southern Cape on 26 and 27 September, 2 and 3 October as well as 7 to 11 October where up to 20mm is possible. Regular light falls again can help to prevent serious drought damage.
3.3 Namibia
Very little or no rain is expected until at least November but average to above average rainfall from the last part of November to February. Temperatures will be warm to hot until about the middle of November when the first rain is expected.
