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Near average rainfall prevailed most of the season but localized deficits appeared in September

  • Seasonal Monitor
  • West Africa
  • September 26, 2017
Near average rainfall prevailed most of the season but localized deficits appeared in September

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  • Key Messages
  • UPDATE ON SEASONAL PROGRESS
  • FORECASTS
  • Key Messages
    • The total rainfall for the first 2 dekads of September (Figure 1 and Figure 2) has been below average over most of the region, with large portions in Niger, Chad, central-western Senegal, the Senegal/Mauritania border area, southwestern Burkina Faso, and northern Ghana affected by severe deficits.

    • Rainfall deficits are a concern for crop and pasture productivity shortfalls in areas that suffer long dry spells (over 8 days) during the first two dekads of September (Figure 3).

    • The ITF started its southward retreat in mid-August and is now at the northern limit of the Sahelian zone (Figure 4),which augurs the normal end of rains in the northern Sahelian zone in late September.

    • The medium-term forecast for the next two weeks (September 23rd– October 7th) calls for dry conditions in the Sahelian zone by early October and moderate to heavy rains south of it.


    UPDATE ON SEASONAL PROGRESS
    • The Intertropical Front’s (ITF) has reached its northernmost position in early August and started its southward retreat around mid-August.  It is now positioned at the northern limit of the Sahelian zone at its climatological position over most of the region except in western Mauritania where it is slightly south of it and in eastern Niger and Chad where it is 1-2 degrees north of it (Figure 3).   This indicates the end of the dry season in the northern part of the Sahelian zone is nearing as confirmed by the medium term forecast for the next couple of weeks (Sept 23 - Oct 7).
    • The “minor dry season” in the bi-modal zone has ended in late August but rainfall has remained below average.  However, based on the medium term forecast moderate to heavy rainfall is expected over the area in the next couple of weeks, which will bring the needed relief for the minor season crops.
    • For the other agro-climatological zones north of the bi-modal zone rainfall was generally above average until the end of August.  The few areas that with below average rainfall only experienced light deficits and benefited from a nice time distribution of rainfall resulting into favorable conditions for crops and pastures.  During the first two dekads of September, however, some areas in the Sahelian zone have experienced severe deficits coupled with a bad rainfall time distribution with dry spells exceeding 8 days.  The impact on crops and pastures is expected to be significantly important, particularly during the reproductive phenological phase (from mid-August to mid-September).  These areas include southeastern Niger (south of Diffa region), central Niger (north of Maradi region) and southwestern Mauritania (southern Trarza and Brakna regions).
    • Based on the FAO desert locust update in early September the situation is expected to remain calm for the rest of the season; despite good rainfall and favorable ecological conditions observed during the last couple of months over the breeding area extending from Mauritania to Chad only small scale breeding is expected.

    FORECASTS
    • The short and medium-term NOAA/CPC’s forecasts call for moderate to heavy rains over the bi-modal and Sudanian-Guinean zones and southwestern Mali, Senegal and Mauritania during the first week (23-30 Sep).  For the second week (1-7 Oct), however, rainfall activities will only concern the Guinean-Sudanian and bi-modal while the Sahelian zone will remain completely dry.  This is indicative of the installation of the dry season over the Sahelian zone by early October.
    • The October seasonal forecast from the NOAA-NCEP calls for climatology over the region.
    Figures Figure 1: Total rainfall estimate (RFE) in mm, 1st and 2nddekads of September

    Figure 1

    Figure 1: Total rainfall estimate (RFE) in mm, 1st and 2nddekads of September

    Source: USGS/FEWS NET

    Figure 2: Rainfall estimate (RFE) anomaly compared to the 2006-2015 mean, in the 1stand 2nddekads of September

    Figure 2

    Figure 2: Rainfall estimate (RFE) anomaly compared to the 2006-2015 mean, in the 1stand 2nddekads of September

    Source: USGS/FEWS NET

    Figure 3: Areas of severe deficit and dry spells longer than 8 days

    Figure 3

    Figure 3: Areas of severe deficit and dry spells longer than 8 days

    Source: USGS/FEWS NET

    Figure 4: Intertropical Front (ITF) position compared to climatological average in 2nd dekad of September

    Figure 4

    Figure 4: Intertropical Front (ITF) position compared to climatological average in 2nd dekad of September

    Source: USGS/FEWS NET

    SEASONAL CALENDAR IN A TYPICAL YEAR

    Figure 5

    SEASONAL CALENDAR IN A TYPICAL YEAR

    Source: 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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