Abstract:
The present study evaluates the performance of a Subseasonal to Seasonal (S2S) model (called
The China Meteorological Administration) in simulating rainfall onset dates (RODs) over West Africa.
Using two ROD definitions, we compared the model's ROD at six lead‐time forecasts (10, 20, 30, 40, 50, and
60 days) with the observed ROD from satellite data sets, statistically quantified the model's capability to
reproduce the interannual variability of RODs over the climatological zones in the subcontinent, and
investigated how well the model links RODs with the dynamics of monsoon system over the subregion. The
results show that the mean RODs follow a latitudinal progression and the dates increases northward
from the coast. The performance of the S2S model in reproducing RODs largely depends on the definition
used. For instance, the ability of the model to replicate the observed spatial pattern of RODs and all the
essential features over the three zones in West Africa is stronger with DEF1 than DEF2. Regardless of the
ROD definition used, the 20‐ to 60‐day forecasts produced more realistic simulation than the 10‐day forecast.
We also found that the performance of the model in reproducing the interannual variability of RODs
depends on the zones (Guinea, Savanna, and Sahel). Moreover, the model could reproduce the three main
phases of the West African Monsoon (the onset, the peak, and the southward retreat of rainfall) and other
dynamics. The results of the study have application in improving S2S forecasting over West Africa.
