WAM Seasonal Forecast
Seasonal forecast of the Sudan-Sahel (10°W – 10°E, 9°N – 18°N) monsoonal rainfall using a multi-linear regression method applied to SSTAs in the Tropics.
There is a link between the precipitation in the monsoonal season (JAS) in West Africa and the SST of the Atlantic and Indian oceans on interannual time-scale. Therefore, we elaborate a statistical method to predict the intensity of the West Africa monsoon in the Sudan-Sahel region, based on the SSTAs.
The JAS rainfall in the Sudan-Sahel region is well correlated with the SSTA in the Equatorial Atlantic in OND, in the South Atlantic in NDJ, and in the West Indian in JFM. We use these 3 sub-basins as predictors for the JAS amount of the Sudan-Sahel monsoonal rainfall, in a lagged multi-linear regression analysis. The probability of detection (POD) is 1.00 for wet events, 0.67 for normal events and 0.80 for dry events.
The set of predictors becomes fully available within 4 months: in January the SSTA in the Gulf of Guinea, in February the South Atlantic, and in April the West Indian. Therefore we provide the forecast in 3 steps, adding each predictor when it is available, having outlooks in January and February, and the final forecast in April.