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Favorable September rainfall likely to offset early season deficits

  • Seasonal Monitor
  • West Africa
  • September 18, 2023
Favorable September rainfall likely to offset early season deficits

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  • Key Messages
  • Update on Seasonal Progress
  • Forecasts
  • Seasonal Calendar in a Typical Year
  • Key Messages
    • The Intertropical Front (ITF) reached its apex and started its southward retreat, but is still north of its climatological position.

    • Seasonal rainfall has been mostly average to above-average, over most of the region.

    • Average to above average forecasts for September will likely offset deficits observed over localized areas of the Sahelian zone in July, notably in southern Mali and northeastern Nigeria.

    • Moisture conditions have been favorable for crop growth and development over most of the region, therefore, harvest is expected to be at least average across most countries in the region.

    Update on Seasonal Progress
    • The Intertropical Front (ITF) reached its northernmost position during the first and second dekads of August and started a slow southward retreat during the third dekad of August. As of the first dekad of September it was located north of its average position throughout the region, when its dekadal average position varied between 20.9°N over Mali and Mauritania and 16.4°N in eastern Chad.
    • Seasonal cumulative rainfall (Figure 1) has been average to above-average over most of the region, though with some slight deficits over localized areas. However, at a monthly timescale severe rainfall deficits affected:
      • Southern Mali, southwestern Burkina Faso, and northeastern Nigeria through southeastern Niger areas in July (Figure 2)
      • The regions of Maradi and Zinder in Niger, an area extending from extreme northeastern Nigeria and Far North Cameroon into Hadjer Lamis region in Chad in August (Figure 3)
      • Also in August the northern parts of Hodh el Gharbi, Assaba, and Brakna in southern Mauritania, Saint Louis region in northern Senegal, and the extreme southwestern part of Timbuctu region in Mali suffered from long dry spells and or rainfall deficits
    • In the Sahelian zone where crops are most sensitive to rainfall deficits, negative rainfall anomalies in August are typically not problematic if rainfall is well distributed in time, because it is the rainiest month of the season during which moisture is almost always adequate for crop and pasture development. Such is not the case for July, during which rainfall deficits could be the cause of significant planting delays and subsequent bad crop/pasture performance. Therefore, significant yield drop is expected over areas like southern Mali, southwestern Burkina Faso, northeastern Nigeria and northeastern Niger that experienced severe rainfall deficits in July.
    • The southward ITF retreat is just beginning, however, if its slow retreat is maintained through the next couple of dekads, a normal to late end of the season is expected, allowing some added time for crops planted with delays to close their cycle. Since the 2023 growing season has been progressing well over most places so far, and given the favorable subseasonal rainfall forecasts for the remainder of the season, an average harvest is expected for the region. 

    Figure 1

    1-April through 31-Jul CHIRPS and August CHIRP Percent-of-Average Rainfall
    April through August Percent of Average Rainfall

    Source: CHC/UCSB

    Figure 2

    July Combined CHIRPS Anomaly-CDD
    July Combined CHIRPS anomaly-CDD


    Figure 3

    August Combined CHIRP anomaly-CDD
    August Combined CHIRPS anomaly-CDD

    Source: USGS/UCSB


    According to the monthly forecasts from NOAA-CPC and CHC-UCSB and WMO (World Meteorological Organization) at least average rainfall is expected through the end of October. This forecast augurs a timely or slightly late end of the season in the Sahelian zone.

    Seasonal Calendar in a Typical Year
    Seasonal Calendar for a Typical Year


    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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