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Despite a late start, the Sahel seasonal rainfall is mostly average to above-average and well distributed

  • Seasonal Monitor
  • West Africa
  • August 31, 2021
Despite a late start, the Sahel seasonal rainfall is mostly average to above-average and well distributed

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  • Key Messages
  • UPDATE ON SEASONAL PROGRESS
  • FORECASTS
  • Key Messages
    • There are clear signs the Intertropical Front (ITF) has reached its northernmost position during the last couple of dekads.  Its southward retreat is expected to start soon.

    • Heavy rainfall of above 200 mm has affected large areas in southwestern Mali, the western half of Guinea, and western Sierra Leone raising flooding concerns.

    • Persistence of dryness around Lake Chad area and extending into Far North Cameroon, is likely to have negative consequences on crops and pastures production.


    UPDATE ON SEASONAL PROGRESS
    • The ITF is located between 16.5 degrees of latitude north in eastern Chad to 21.3 degrees in Mauritania as of the end of the second dekad of August around its climatological position over most of the region (Figure 1).  For the last three dekads the Intertropical Front (ITF) has been going back and forth around the same position throughout its regional extent.  Considering the warm current and forecast Gulf of Guinea SSTs, this is an indication that the ITF has reached its northernmost position for the current season.  Its southward retreat is expected soon.
    • The delayed ascent of the ITF this season has resulted in rainfall deficit that persisted over 2 large portions of the Sahelian zone till mid-July.  This early season Sahelian deficit areas included an area covering Niger, northern Nigeria and extending into western Chad and another one in the extreme western Sahel extending from eastern Senegal into central southern Mauritania.  Beginning from mid-July, the rainfall situation over the region has improved resulting in a significant decline in the rainfall deficits. The seasonal cumulative rainfall from May 1st to August 25 (Figure 2) has been above average over most of the region.  However, negative impact of dryness on crop and pasture development over areas where dryness has persisted for a very long time such as Far North Cameroon and Lake Chad is expected.

    FORECASTS
    • According to the short and medium term forecasts from NOAA-CPC, rainfall is expected to continue over the whole region including the northern edge of the Sahelian zone and no significant dry spells are expected within the next two weeks.  This forecast combined with average to above average and well distributed rainfall observed so far favors an average to above average harvest.
    • The NOAA-CPC Northern American Multi-Model Ensemble (NMME) monthly forecast for September and October all generally predict average to above average seasonal rainfall conditions over most of the region.
    Figures

    Figure 1

    Figure 1

    Source: NOAA/CPC

    Figure 2

    Figure 2

    Source: USGS/FEWS NET

    FEWS NET’s Seasonal Monitor reports are produced for Central America and the Caribbean, West Africa, East Africa, Central Asia, and Somalia every 10-to-30 days during the region’s respective rainy season(s). Seasonal Monitors report updates on weather events (e.g., rainfall patterns) and associated impacts on ground conditions (e.g., cropping conditions, pasture and water availability), as well as the short-term rainfall forecast. Find more remote sensing information here.

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