Together with the late rainfall over the winter rainfall region, dry weather dominated the summer rainfall region. This pattern was reflected over the entire Southern Hemisphere by a northward displacement of westerly winds – or a weakening of high-pressure systems at 40° Latitude. The weakening of high-pressure systems at this latitude is usually associated with weaker easterlies and therefore less moisture over the southern African interior and concomitant lower rainfall than the norm. This pattern contributed to relatively low rainfall over the summer rainfall region during October together with above-normal maximum temperatures, especially over the northern to northeastern parts of South Africa. Concerning Sea Surface Temperatures (SSTs), global patterns reflect anomalies usually associated with lower rainfall than the norm over southern Africa – and higher rainfall over Equatorial East Africa. Most importantly, these include:
• Anomalously warm SSTs over the central equatorial parts of the Pacific Ocean .These are not at El Niño thresholds though.
• Anomalously high (low) SSTs over the western (eastern) Tropical Indian Ocean. This represents a strong positive Indian Ocean Dipole – a pattern that is weakly associated with dry conditions over southern Africa and wet conditions over Equatorial East Africa.
Given the current SST anomaly patterns across the Globe, seasonal forecasts from most international institutions favor El- Niño-like rainfall patterns over sub-Saharan Africa. This includes anomalously dry (and warm) conditions expected over the summer rainfall region for most of the coming summer.
El Niño and seasonal forecasts
The Australian Bureau of Meteorology notices a very strong Positive Indian Ocean Dipole event and expect the phenomenon to weaken. They also point out that ENSO is in a neutral state:
(Updated 29 October): In the tropical Pacific Ocean, waters have warmed over the past month but have caused little change in the atmosphere, and hence the El Niño–Southern Oscillation (ENSO) remains neutral. The latest 30-day Southern Oscillation Index (SOI) is –5.2, returning it to more neutral levels.
The majority of climate models forecast neutral ENSO for the remainder of 2019 and into the first quarter of 2020. When ENSO is neutral, it has little effect on Australian and global climate, meaning other influences are more likely to dominate........Australian Bureau of Meteorology -
The seasonal forecast by the IRI for Africa favours relatively warm and dry conditions for both early and late summer 2019/20 over South Africa. There is still a signal for relatively wet conditions over the winter rainfall region in the November – January period. The dry signal is slightly stronger in early than late summer according to these forecasts. Coupled with the relatively dry conditions, the interior is also expected to be somewhat warmer than the norm – especially towards late summer.
Based on the typical observed rainfall patterns over the summer rainfall region, as associated with the cyclic variability of the global climate system, similar summers as 2019/20 more often experience relatively wet mid-summers (November – January) while the spring months tend to be dry (September / October). Another relatively dry period in such summers tend to centre on February, with weaker indications for relatively dry conditions in the surrounding months (January and March). There is also a tendency for relatively wet conditions centred on April. These tendencies for intra-seasonal rainfall variability are shown in the figure below.
Typical patterns in similar summers are:
• Relatively wet conditions over the winter rainfall region during September – October
• A tendency for relatively wet conditions during early to mid-summer over especially the central parts of the summer rainfall region. These wet conditions typically only start in November, following dry conditions in September and October.
• A tendency (more often than not) for relatively dry conditions in late summer, especially over the northeastern parts of the country.
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