Important Issues:
- Rain possible in the second week of March over the Summer Rainfall Area but a second dry spell can occur in the last part of March.
- La Nina and the positive Southern Oscillation Index (SOI) can still be responsible for further rain in April and May.
- Hot and dry conditions will continue over the Western Cape, especially the central to western parts.
Current conditions
After a very wet period since December 2021, was the month of February in general dry with only smaller areas that received significant rain. Parts of the Northern Cape received good falls in the first week of February with Noupoort 81mm, Petrusville 70mm and De Aar 34mm. The Bridle drift dam area in the Eastern Cape received more than 80mm. Heavy falls also occurred in the first week of February like Pretoria 82mm, Vereeniging 50mm, Charters Creek in KZN 114mm and Richards Bay 92mm. The rest of February was in general dry with significant rainfall that only occurred over the northern parts of the Eastern Cape with Elliot 36mm and Queenstown 22mm and parts of KZN like Greytown 34mm and Pongola 41mm.
The dry conditions since the second week of February and even earlier in parts of the eastern Free State and Mpumalanga is now resulting in some drought damage to summer crops in areas with shallow soils. Root development is also restricted due to initial very wet conditions with roots that only developed in the upper parts of the soil.
Very dry conditions still prevail in smaller pockets in the Eastern Cape, but the drought has been broken in most parts of the Northern Cape.
Nearly all dams in the Summer Rainfall Area are at very high levels due to the heavy rains until the end of January. The average level of Free State dams was still at 102% in the last week of February. Only some dams in the Eastern Cape are still suffering low levels although there was a rise in levels. The Kouga dam dropped however again to below 16%. while the level of the Bridle drift dam increased from very low levels to over 63% at the end of February compared to 33.9% last year the same time.
The water level in Lake Kariba in Zambia is at about 23% compared to about 32% last year the same time while the Katze dam in Lesotho is at 100% and the Mohale dam at 70%. The Hardap dam in southern Namibia was at the end of February 2022 at 73% of full volume.
2. ENSO and Indian Ocean
2.1 ENSO (El Nino Southern Oscillation)
Sea surface temperatures in the Nino areas reached a peak towards the end of January 2022 and is La Nina is now weakening. Temperatures in most of the Nino- areas are showing a slight warming trend and the important Nino3-4 area was in the last week of February about 0.6°C cooler than normal compared to the peak in January 2022 of about 1.1°C cooler than normal. Subsurface water temperatures also showed a slight warming trend.
La Nina conditions will remain present until at least early winter when it will return to neutral conditions. ENSO is usually in a neutral state from about April to June when changes start to develop before the start of the Southern Hemisphere summer. Current forecasts for ENSO conditions for the 2022/23 summer season are very inconclusive with an about 45% probability for neutral conditions to continue from late autumn, a 35% probability for La Nina and a 20% El Nino, respectively. More certainty will only be available from about July 2022 what to expect for the next summer season. Forecasts however showed an increased probability since January favouring La Nina at the cost of neutral and El Nino. In January was the probability about equal split between La Nina and El Nino and a more than 50% probability for neutral conditions.
The Southern Oscillation Index (SOI) as indicator of the effect of sea surface temperature interaction with overlying weather systems in the Nino areas, again shows a more La Nina trend compared to January 2022. On a scale from -30 (Strong El Nino) to +30 (strong La Nina) is the current 30-day average SOI about +9.9 from a low in January of about +1.5.
2.2 Indian Ocean`
The Indian Ocean Dipole Index (IOD) remains in a neutral state and forecasts are showing that it will remain neutral until at least April when it will move more towards the negative IOD phase. (A negative IOD is positive for summer rainfall indicating cooler surface water of the western Indian Ocean towards the African coast as was the case in 2021).
Five relative strong tropical systems developed since the last week of January, causing serious damage in Madagascar and in Mozambique and Malawi on the Africa continent. Cyclone Batsirai was the most intense with wind speeds of more than 200km per hour, causing serious damage in Madagascar with more than 250mm of rain associated.
3. Rainfall and Climate
3.1 Summer Rainfall Area
Rainfall
The strengthening of the Southern Oscillation Index (SOI) in February despite a weakening La Nina is significant and can be responsible for more rain in late autumn.
- The recent series of tropical systems disturbed the normal weather patterns and prevent the movement of tropical moisture to the south by channelling it more to the east towards the tropical systems.
- Conditions for rain will improve in the first week of March following the disappearance of cyclone Emnati. Between 20mm and 50mm is possible from about 3 to 10 March over most of the country with the exception of the western parts of the Northern Cape, most of the Western Cape, western parts of the Eastern Cape and northern parts of Limpopo.
- Drier conditions are possible in the second part of March.
- Due to the presence of La Nina is rain still possible in the last week of March and April.
Temperature
- Temperatures will be average to above for most of March but cooler in April.
- The probability for early frost is very low and severe frost is not expected before the middle of May.
3.2 Winter Rainfall Area
Very little rain is expected over the central to western parts of the Western Cape for March, but smaller amounts of rain are possible over the South Coast and Garden Route. The start to the winter rainfall season resulting from frontal systems that will originate from the southern Atlantic, is likely to be very late, only from May or even later.
Temperature
Hot to very hot conditions are expected to continue until at least the end of March, especially over the central to western parts of the Western Cape with cooler conditions over the South Coast and adjacent interior.
3.3 Namibia
Tropical moisture started to move from Angola and central Africa over Namibia on the perimeter of the high-pressure system over most of South Africa, Botswana and even Zimbabwe. Rain is expected over the northern parts until about the second week of March.
Longer term outlooks for rainfall are still very positive in the pre-winter period. The impact of La Nina is still eminent for average to above average rainfall to occur.
4. Summary and conclusion
- La Nina reached maturity in the middle of January 2022 but will still impact on rainfall and climate conditions until late autumn with more rain to come.
- Rain is again expected in the first week of March over the central to eastern and south- eastern parts of the country. A drier spell is again possible in the second part of March over the central to western parts.
- The south-western parts of Winter Rainfall Area can still expect dry and hot conditions until at least the end of March. Light falls are however possible towards the Rûens and South Coast.
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