Assessment the 1999 Sahel summer rains and seasonal forecast verifications

Sahel rainfall exhibits a clear decadal signal with a period of above normal rainfall in the 50s and 60s and a long stretch of dryness that began in 1972. The 1999 Sahel rainfall season was the wettest since 1972, but only the 10th wettest since 1950. NCEP/NCAR reanalysis data and OI SST data are used to assess the Sahel rainfall during the 1999 season. The influence of the cold ENSO event is addressed. It is shown in particular that strong low level velocity convergence was present in the Gulf of Guinea region associated with a well defined African Easterly Jet (AEJ) exhibiting a clear axis centered around 15N. This axis of the AEJ was located at the equatorward flank of the cyclonic shear zone where much of the African waves and their associated cloud systems developed. It is also shown that the Tropical Easterly Jet (TEJ) was well defined and extended well into the Atlantic Ocean. Predictions for the Sahel rainfall at one month lead based on CCA and using global SSTs as predictor field were also made and verified against observations.