Important Issues:
La Nina continues at relative moderate to strong levels.
The first significant rain is possible from about the middle of June over the Winter Rainfall Region. Heavy falls may result in damage to infrastructure and crops.
Current conditions
Heavy “unexpected” rain continued during May. More than 300mm was recorded on the weekend from 20 to 23 May in parts of KZN, causing flooding conditions for the second time in two months. More than 50mm were also recorded in other parts of the country like Cradock in the Eastern Cape (55mm), Koppies in the Free State with more than 100mm, Greytown in KZN with 51mm and Kathu in the Northern Cape with 63mm.
The rain in the Summer Grain Area caused damage to harvest-ready crops like soya beans, dry beans and sunflower but it will help to postpone the start of the fire season due to high humidity and wet soil surface conditions. Rain in the Eastern Cape was now for the first time sufficient to break the drought in areas like Cradock and Jansenville but there are still areas suffering from drought.
The coldest week of winter was recorded between 30 and 31 May. The lowest temperatures were Sutherland -7.9°C, Buffelsfontein near Molteno –6.0°C, Prieska -5.5°C, Bloemfotein -5.2°C, Wesselsbron -4.0°C and Calvinia -4.4°C.
Most storage dams in the Summer Rainfall Area are still at very high levels with the Vaal dam at 109%, Bloemhof dam at 104.6%, Vanderkloof dam at 99.0% and Gariep dam at 100.2%. Western Cape dam levels are on average at about 51.9% compared to 53.9% the same time in 2021. The Kouga dam in the Eastern Cape is below 13% and the Impofu dam at 10.3%.
The water level in Lake Kariba in Zambia is at about 32.8% compared to 53.0% last year the same time while the Katze dam in Lesotho is at 97.8% and the Mohale dam at 97.4%. The Hardap dam in southern Namibia was at 19 Mei 2022 at 69% of full volume while the largest storage dam, the Neckartal dam, is at 99.2%.
2. ENSO and Indian Ocean
2.1 ENSO (El Nino Southern Oscillation)
All the Nino-areas are still cooler than normal with the important Nino3.4-area on -1.0°C cooler than normal. Of importance is the high index values of the Southern Oscillation Index (SOI) that is a measure of coupling of weather and surface conditions. The 30-day running average of the SOI was on 2 June 2022 on a scale from +30 (La Nina) to -30 (El Nino) at a value of +17.94 and the 90-day value on +16.3.
The probability for a full scale La Nina in the next at least six months to continue, is about 60% with El Nino conditions about 5% probability to occur.
It is likely that the La Nina intensity will weaken in the July to September period but is still expected to maintain weak La Nina conditions. Current forecasts indicates that La Nina will return to neutral conditions early in 2023.
2.2 Indian Ocean
The Indian Ocean Dipole Index (IOD) is currently in a neutral phase, but the latest forecasts indicate a sharp drop towards the negative phase from about June to at least September. (A negative IOD is positive for summer rainfall, indicating cooler surface water towards the western Indian Ocean (African coast) and warmer water towards Australia, as was the case in 2021).
3. Rainfall and Climate
3.1 Summer Rainfall Area
Rainfall
The rainy season, even with La Nina-conditions present, is likely to cease with only some parts of the country to expected further rain in the coming months like the eastern and south-eastern Summer Rainfall Area.
The expected negative phase of the Indian Ocean Dipole (IOD) index to develop in the next months is a very positive signal for rainfall in the post-winter period and in conjunction with the La Nina, can again be responsible for above average rainfall in the 2022/23 summer.
The probability for average to above rainfall is still favourable for the eastern and south-eastern areas but unfavourable for the central to north-western parts for at least until October/November.
A dry spell is expected from about June to November that is in line with La Nina conditions.
Average to above average rainfall is again expected from about November 2022 over the eastern production areas and shifting towards the central and western parts in the mid- to second part of summer.
Temperature
Severe frost started to occur towards the end of May and is likely to continue through June and July.
It is most likely that sporadic frost can continue until at least September and even October, causing a high frost damage risk to winter wheat and early varieties of grapes, pecan nuts and other frost sensitive crops.
3.2 Winter Rainfall Area
Rainfall conditions are in general below average up until the end of May, but it is expected that heavier falls of rain are possible from the middle of June. More than 30mm to 50mm is possible from about 14 to 23 June over most of the Winter Rainfall Area. Heavy falls are possible with the potential to result in damage. Lighter falls of rain is possible along the West Coast as high as Springbok and adjacent areas during this period.
Temperature
Temperatures will be mild up to the middle of June but cooler due to rain and very cloudy conditions from about 13 June.
3.3 Namibia
Not much further rain is expected for the winter and spring but average to above average rainfall is possible from about November.
4. Summary and conclusion
Moderate La Nina conditions continue but is likely to weaken somewhat from July to September. It will however maintain La Nina levels until at least midsummer.
Short term outlooks are becoming unfavourable for most of the Summer Rainfall Area, except for the eastern to south- eastern areas where there is still a chance for rain.
Heavy rain of more than 30mm to 50mm is expected for the Winter Rainfall Area from about 14 June.
