West African Monsoon Demise

The northward progression of the precipitation maximum across West Africa in the boreal spring is not smooth, being characterized by a “monsoon jump” that moves rainfall from the Guinean coast region (near 5S) into the Sahel (about 15N) over a few days' time. In contrast, the southward retreat of the precipitation maximum in the fall is smooth. Here we examine precipitation observations and reanalyses to understand the reasons for this difference. The degree to which the end of the rainy season in the Sahel is correlated with the location of the subsolar point and the breakdown of the Atlantic cold tongue is evaluated, and the implications for seasonal prediction of the end of the monsoon season are discussed.