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Above average rainfall in September ended the unusually long minor dry season in the bimodal zone

  • Seasonal Monitor
  • West Africa
  • September 28, 2020
Above average rainfall in September ended the unusually long minor dry season in the bimodal zone

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  • Key Messages
  • Update on Seasonal Progress
  • Forecasts
  • Key Messages
    • The Intertropical Front (ITF) has started its southward retreat (Figure 1), which is a clear indication that the dry season in the Sahelian zone is nearing.

    • Above average rainfall during the last 30 days resulted in a significant improvement of the cumulative seasonal rainfall in the western Sahel (Figure 2).

    • From late August to early September heavy and frequent rains caused flooding along major rivers.

    • The significant rainfall amounts received since the beginning of September in the bimodal zone has allowed the start of the minor growing season.

    Update on Seasonal Progress
    • The Intertropical Front (ITF) has started its southward seasonal retreat in early September.  It was positioned between 15 to 17 degrees north during the second dekad of September.  The retreat has been significant and is now 2 to 3 degrees south of its climatological position throughout the region.  This is a clear sign that the end of the growing period is nearing in the Sahelian zone.
    • Throughout the current rainy season, the region has received mostly average to above average and well distributed rainfall.  Very few localized areas of limited size have experienced dryness.  Most of these deficits have been mostly light to moderate and short lived.
    • The heavy rainfall recorded frequently over most of the region from late August to early September, and high soil moisture have caused flooding in many parts of the region, particularly along the major rivers.  According to Reuters these floods have affected about 760,000 people in West and Central Africa. Burkina Faso, Cameroon, Chad, Ghana, Mali, Niger, Nigeria and Senegal are among the worst hit with at least 111 fatalities according to OCHA.
    • The western Sahel, Senegal-Mauritania border area, and the bimodal zone were affected by severe deficits and long dry spells that persisted from June through the end of August.  However, these areas have received above average rainfall since the beginning of September as (Figure 1 and Figure 2)
    • The significant rainfall activity in the bimodal zone as a result of the southward retreat of the ITF has put an end to the longer than normal minor dry season and has indicated the start of the minor growing season.

    • According to the short and medium term forecasts from CHC/UCSB and from NOAA/CPC above average rainfall is expected over areas south of the Sahelian zone, and no significant dry spells are expected within the next four weeks.
    • The NOAA-CPC Northern American Multi-Model Ensemble (NMME) seasonal forecasts for October, the final month of the season, generally predicts climatology to increased chances for below average rainfall.
    Figures Map of ITF position in September compared to normal: Slightly lower than normal in the west and higher than norrmal in the ea

    Figure 1

    Figure 1.

    Source: NOAA

    Map of 3rd dekad of August – 2nd dekad of September total rainfall estimate (RFE) anomaly compared to the 2009-2018 mean : Mo

    Figure 2

    Figure 2.


    West Africa seasonal calendar  In the North, Main season cultivation is from mid-May to mid-August. Main harvest is from mid-

    Figure 1


    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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