Spatio-Temporal Variability and Predictability of Relative Humidity Over West African Monsoon Region

The spatial locations of the clusters in the three periods are shown in Figure 3. In all the periods the three clusters exhibit a clear north-south spatial pattern with stations grouped along east-west. The north-south stratification is consistent with movement of the ITCZ through the monsoon season and the background strong climatological humidity gradient in the region. The stations in the three clusters for the onset and retreat periods are almost similar identical with slight changes differences only at the cluster boundaries. This similarity can be attributed to the onset northward and retreat southward movement of the ITCZ being fairly uniform. The onset ITCZ transition includes a ‘jump’ from ~10º to 15º N in June, contrasted with a relatively smooth retreat, but averaging the relative humidity over each period obscures these differences. During the peak season the ITCZ is within 10º to 15º N latitudes, hence the diffusion of cluster boundaries. Several of the stations found in the northern cluster during onset and retreat are found in the middle cluster during peak monsoon period. Only the three most northern stations, Tombouctou, Gao, and Agadez, all located close or within the Sahara remain in the northern cluster in all three periods.

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