The African Monsoon Recent Evolution and Current Status

1. The African Monsoon Recent Evolution and Current Status Update prepared by Climate Prediction Center / NCEP 29 September 2008 For more information, visit: http://www.cpc.ncep.noaa.gov/products/Global_Monsoons/African_Monsoons/precip_monitoring.shtml

2. Outline • Highlights • Recent Evolution and Current Conditions • NCEP GEFS Forecasts • Experimental Week-1 and Week-2 Outlooks • Summary

3. Highlights:Last 7 Days • Moderate to heavy rains sustained moisture surpluses over the western part of the Sahel, while the central and eastern areas received beneficial rains. • Moderate to heavy showers continued to ease dryness in many areas in Sudan. • Western Ethiopia continue to receive beneficial rains.

4. Rainfall Patterns: Last 180 Days Over the past 180 days, rainfall was above average over most areas in West Africa and central Africa, except for pockets in northern Nigeria. Rainfall was also above average over western Ethiopia. Rainfall was below average over portions of the Greater Horn of Africa, including eastern Sudan.

5. Rainfall Patterns: Last 90 Days Over the past 90 days, rainfall was above average over most areas in West Africa, including the central and western part of the Sahel and much of the Gulf of Guinea region. Rainfall was near average in the eastern part of the Sahel. Drier than average conditions prevailed over central Sudan, while western Ethiopia received above average rainfall. Rainfall was also above average over central Africa.

6. Rainfall Patterns: Last 30 Days Over the last 30 days, rainfall was above average over most areas in the western part of the Sahel, but near average in the central areas. Most areas in the Gulf of Guinea region received above average rainfall. Rainfall was also above average over much of central Africa, southern Sudan, and western Ethiopia.

7. Rainfall Patterns: Last 7 Days During the past 7 days, rainfall was near average over most areas in the Sahel, except for the western end, including eastern Senegal. Rainfall was above average along the western edge of the Guinean coast, portions of Benin, Nigeria, and parts of central Africa, and southern Sudan.

8. Recent Rainfall Evolution Over the past 30 days, cumulative rainfall continued to be above average in the western end of the Sahel (bottom panel – left). Persistent light rains over the past two weeks resulted in near average cumulative rainfall in the central areas of the Sahel (top panel – right). Cumulative rainfall was slightly below average over parts of the Gulf of Guinea region (bottom panel - right).

9. Atmospheric Circulation:Last 7 Days Over the past 7 days, the 850 hPa wind anomaly (left panel) featured westerly anomalies from the tropical central Atlantic eastward into the Guinean coast. Also featured was an anomalous cyclonic circulation centered off the east coast of South Africa. The 200hpa wind anomaly featured a strengthening of the subtropical ridges in both hemisphere across the Atlantic.

10. NCEP GEFS Model ForecastsNon-Bias Corrected Probability of precipitation exceedance Week-1: Valid 30 September – 06 October, 2008Week-2: Valid 07-13 October, 2008 For week-1 and week-2, NCEP global ensemble forecast system (GEFS) suggests a 90% chance or more for precipitation to exceed 50 mm along the Guinean coast and parts of central Africa. Note: The GFS tends to suppress (increase) precipitation in the Sahel (Gulf of Guinea region).

11. Experimental Week-1 Precipitation OutlookValid 30 September – 06 October, 2008 Precipitation climatology for the verifying period Climatology is expected during the period

12. Summary • Over the past 7 days, moderate to heavy downpours continued to fall over many areas in West Africa resulting in above average rainfall in the western sectors of the Sahel and near average rains in the east. Much of the Gulf of Guinea region continued to receive above average rainfall. The exceptions were Cote d’Ivoire, Ghana, and eastern Nigeria, where rainfall was bear average. • Over the past 30 days, persistent rains resulted in moisture surpluses over the western Sahel, including Senegal and western Mali. A weakening of the rainfall intensity over the past tow weeks resulted in near or slightly below average cumulative rainfall over many areas in the central and eastern Sahel, including portions of southern Mali, eastern Burkina Faso, and southern Niger. The Gulf of Guinea region, central Africa, and portions of Sudan, and western Ethiopia were overall wet over much of the period than and Gulf of Guinea. The rainfall increase in Sudan was associated with persistent moderate to heavy showers over the past two weeks. • For the week1 ending 06 October and week2 ending 13 October, 2008, climatology is expected over most areas in Africa.