For 3 consecutive years, across Namibia, we have had a regular advection of Congo air which has, predictably, brought substantial rains. Being in the third year, with similar input on show, there must be concern about the ability for this current pattern to persist further down the rainfall season line.
There is good reason for this concern. Whereas the past 2 seasons featured, for at least a few months, a La Nina sea-surface temperature pattern dominating the equatorial Pacific and hence a positive value to the Southern Oscillation; currently there are differences. For this new millenium, the climate world recognizes increased warmth and a resultant effect producing a change of climate patterns. Since the winter months, sea-surface temperatures have become anomalously warm across mid and, later, eastern Pacific. Briefly, such warm waters reached the South American coast. This has its own, well-known description: El Nino.
For climates, around the world this name spells impact, often a detrimental departure from a norm.
El Nino’s warmth is the natural response to a decline in Trade Wind flow and its ability to limit warming across the same equatorial Pacific. The impact of climate change has squeezed the surface core of the sub-Tropical High Pressure belt to latitudes some 5 to 10o south of their normal route. Their ability to support Trade Wind flow has, more-or-less collapsed: no cooling, therefore warming (with the Sun overhead) so the El Nino temperature thresholds are exceeded.
The negative Southern Oscillation is not so readily discernible. Anticyclones track further south, so Tahiti air pressures tend to be lower, but the Indonesian ITCZ   shows a presence around 10S, lying across the other keystone Oscillation benchmark station of Darwin.
Now, does this still mean a negative impact on our rainfall? ENSO history shows varying features for our rainfall season: earlier rains, limited intensities, breaks  upsetting both time and spatial distribution and an early close to the season are disappointing features. When these features all combine, harsh drought is to be experienced. Modification can lead to a poor, but not disastrous, season.
Where are we now?
Early rains, a response to tropical air advection, have occurred. While a consistent rainfall pattern, likewise, developed and persisted across mid-continent. Recently, heavier falls have made their mark Continuance of the current pattern seems to be offered by the longer distance models. This morning’s charts shows the El Nino temperature ranges continuing to retreat to the mid-equatorial Pacific as Trade Wind flows from stronger anticyclones (that bit closer to Tahiti) extend to the east Pacific Equator.
For most of the past fortnight, the Australian surface maps show a persistent ITCZ presence around the 10 to15S latitude from the mid-Indian Ocean across Arnhem land (Darwin) into the northern Tasman sea. This surely cannot be seen as the rise in air pressure required to match the negative stance of the Southern Oscillation Wind flows across Africa indicate an ITCZ presence above central Angola, Katanga and northern Zambia with a southward extension, light and variable flows, into Namibia. Tropical air influence shows no sign of departure for at least some 15 days.