Interdecadal variability of the relationship between the Indian Ocean zonal mode and East African coastal rainfall anomalies

The variance of the rainfall during the October-November-December (OND) "short rain'' season along the coast in Kenya and Tanzania correlates strongly with sea surface temperature (SST) in the Indian Ocean between 1950 and 1999. A zonal pattern of positive correlation in the Arabian Sea and negative correlation southwest of Sumatra forms in the summer preceding the rainy season. The positive correlation strengthens in the western Indian Ocean and the negative correlation in the eastern Indian Ocean weakens in the subsequent fall concurrent with the short rain. Reduced OND East African rainfall is associated with the reversed SST pattern. The OND rainfall also correlates strongly with ENSO. The SST-rain correlation pattern breaks down between the years 1983 and 1993, as does the correlation with ENSO. However, between 1994 and 1999 the OND rainfall, ENSO, and the SST zonal mode again return to strong correlation, as in the years preceding 1983.