The decline in tropical-extratropical cloud bands and the delay of the southern African monsoon.

Weak or delayed onsets to summer rains in southern Africa are becoming a growing risk. For example, the 2024 wet season start was late across countries in the region including South Africa, Zambia, and Malawi. This followed the El-Nino related drought across the region during the 2023/2024 season, illustrating risks of successive planting season challenges. Climate model ensembles project increased risk of early season drying through the coming decades.

In this contribution we explore the link between delayed southern African monsoon onset and decline in tropical-extratropical cloud bands over the more southern subtropical parts of the continent. Such declines are most profound in the regional convection-permitting for Africa (CP4-Africa) model and we interpret this within the context of CMIP model projects.

We conclude with results questioning whether these risks can be forewarned on a season-to-season basis with current S2S forecast systems. At the seasonal forecast lead-time, the answer appears to be no. However, week 2 and possibly week 3 subseasonal forecasts may have dry/wet spell skill which should be exploited in early warning systems, underpinned by more research on Rossby wave predictability.