The African Monsoon Recent Evolution and Current Status

1. The African Monsoon Recent Evolution and Current Status Update prepared by Climate Prediction Center / NCEP 15 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 central areas of the Sahel, while the west received beneficial rains. • Moderate to heavy showers eased 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 and southern Chad. 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, central Africa, and western Ethiopia. Below average rainfall persisted over Sudan.

6. Rainfall Patterns: Last 30 Days Over the last 30 days, rainfall was above average over most areas in West Africa, including the Sahel and the Gulf of Guinea region. Rainfall was also above average over western Ethiopia. Isolated areas in southern Chad received below average rainfall.

7. Rainfall Patterns: Last 7 Days During the past 7 days, rainfall was near average over the western part of the Sahel and above average in the eastern areas southward to the eastern sectors of the Gulf of Guinea region. Rainfall was below average in the western part of the Gulf of Guinea region. Further to the east, rainfall was above average over Sudan and Ethiopia.

8. Recent Rainfall Evolution Over the past 30 days, despite a short break over the past week, cumulative rainfall continued to be above average in the western end of the Sahel (bottom panel – left). The central areas in the Sahel benefited from moderate to heavy rains during the past week (top panel – right). Cumulative rainfall remained below average in the southeastern 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 along the equator eastward into the Guinean coast. There are also westerly wind anomalies in the tropical north Atlantic into Africa. The 200hpa wind anomaly featured a strengthening of both the southern hemisphere subtropical jet in the Atlantic and the St Helen High. Equatorial easterly wind anomalies were confined to the western Indian Ocean.

10. NCEP GEFS Model ForecastsNon-Bias Corrected Probability of precipitation exceedance Week-1: Valid 16-22 September, 2008Week-2: Valid 23-29 September, 2008 For week-1, NCEP global ensemble forecast system (GEFS) suggests a 90% chance or more for precipitation to exceed 50 mm along the Guinean coast and western Ethiopia. For week-2, there is 90% chance or more for precipitation to exceed 50 mm along the Guinean coast. Note: The GFS tends to suppress (increase) precipitation in the Sahel (Gulf of Guinea region).

11. Experimental Week-1 Precipitation OutlookValid 16-22 September, 2008 Climatology is expected during the period

12. Summary • Over the past 7 days, rainfall diminished over the western part of the Sahel and was near average, while the central areas benefited from moderate to heavy showers that brought the cumulative rainfall over the past 30 days back to above average. However, rainfall was slightly below average in the western part of the Gulf of Guinea region and above average in the east. Sudan and Ethiopia received beneficial rains. • Over the past 30 days, persistent rains resulted in moisture surpluses over large parts of the western Sahel and Gulf of Guinea. The rains also fell steadily over western Ethiopia resulting in above average conditions in this region. Rainfall increased significantly in Sudan as a result of persistent moderate to heavy showers over the past week. • For the week1 ending 22 September, 2008, there is an increased chance for below average rainfall over the western sector of the Sahel.