Seasonal forecasting of the Kenya coast short rains, 1901–84

Abstract A rainfall anomaly time series for the Short Rains (September to December) on the Kenyan Coast (KCS) is derived for the period 1901–84. On the year‐to‐year time scale a high degree of association can be seen between high/low extremes of a Southern Oscillation Index and negative/positive anomalies in the KCS series. The SOI‐rainfall relationship is investigated seasonally with KCS lagging the SOI series by one, two and three seasons. A decay of the correlation with increasing lag can be seen. When the time series is divided into 1901–42 and 1943–84 the relationships are stronger in the more recent period. Some forecasting skill does seem possible using the June to August (JJA) SOI to predict the September‐December rains. While the 1901–42 period shows a skill not much improved from using a simple climatological forecast, the 1943–84 period shows a much stronger relationship. Possible reasons are discussed for the disparity between the two time periods, also evident in results from others parts of Africa and Asia. There may well have been a change in some underlying climate mechanism between the early decades of this century and the more recent decades.