Extratropical wavetrain from ENSO drives summer seasonal prediction skill for South Africa

There is a well-established relationship between the El Niño-Southern Oscillation (ENSO) and summer climate over South Africa. ENSO predictability has formed the basis for seasonal forecasting efforts in the region. However, prediction skill over South Africa is not as high as in some other ENSO-dominated regions and there have been notable forecast failures during ENSO events. Here we examine near-term predictions of South African summer climate from two modelling centres and find evidence of a useful level of prediction skill but with an ENSO teleconnection that is weak in amplitude. We describe a Pacific-to-southern Africa wavetrain in the extratropical westerlies, which is a robust feature of the reanalysis and the modelling systems, and which plays a role in the transmission of the ENSO signal to South Africa. Further, we find that a failure of the ENSO teleconnection with South Africa is accompanied by a distortion of the wave over the South Atlantic, manifesting as a change in phase and/or position. This supports the idea that the wavetrain is a key component of the teleconnection.