Tropical Lows in Southern Africa: Tracks, Rainfall Contributions, and the Role of ENSO

Tropical lows are storms that are a bit like very weak tropical cyclones. They occur in summer in tropical regions. This paper tracks individual tropical lows across southern Africa in weather records from the last 39 years. We then look at how they behave, how much they rain, whether they interact with other storms, and how they vary from year to year. About 33 tropical lows are found each year, and they tend to cluster in eastern Angola. We find that 31% of rainfall in the region surrounding Angola and Zambia comes from tropical lows. The number of tropical lows that form in a summer is really important for whether that summer will be unusually dry or wet, particularly along the northern border of Namibia. The number of tropical lows that form in each year is related to the El Niño–Southern Oscillation and also to the winds high up in the atmosphere. In the El Niño phase of El Niño–Southern Oscillation cycle, which usually causes drought in southern Africa, tropical lows form less frequently and further north. In the La Niña phase, which is usually wet in southern Africa, tropical lows form more frequently and further south.