The African Monsoon Recent Evolution and Current Status

1. The African Monsoon Recent Evolution and Current Status Update prepared by Climate Prediction Center / NCEP 16 August 2010 For more information, visit: http://www.cpc.ncep.noaa.gov/products/Global_Monsoons/African_Monsoons/precip_monitoring.shtml Note: Rainfall analysis for Africa is based on satellite rainfall estimates (RFE) and not on actual rain gauge observations.

2. Outline • Highlights • Recent Evolution and Current Conditions • NCEP GEFS Forecasts • Summary

3. Highlights:Last 7 Days • During the past seven days, heavy rains resulted in local flooding in parts of the Sahel, including the western areas of Burkina Faso and Mali, as well as southern Mauritania, and north and central Senegal.  Heavy rains also soaked southern Chad and local areas in northern Ethiopia.

4. Rainfall Patterns: Last 7 Days During the past seven days, moderate to heavy rains fell across most areas in the Sahel. Areas that registered above average precipitation included portions of southern Niger, the western sectors of Burkina Faso and Mali, southern Mauritania, as well as northern and central Senegal, The Gambia, and Guinea Bissau. Rainfall was also above average over portions of the northern areas of the Gulf of Guinea region from Benin to Cote d’Ivoire, as well southern and western Nigeria. Rainfall was locally below average over Sierra Leone and southern Guinea. The northern part of central Africa, including southern Chad, and northern Ethiopia received above average rainfall.

5. Rainfall Patterns: Last 30 Days During the past 30 days, rainfall was highly above average over most areas in the Sahel from Niger to southern Mauritania and eastern Senegal. A few exceptions included western Niger, which registered slightly below average rainfall. In contrast, rainfall was below average over the Gulf of Guinea region, except of southern Nigeria, where rainfall was above average. In central Africa, rainfall was above average over the southern half f Chad and CAR. Rainfall was also above average over northern Ethiopia. Rainfall was below average over most portions of DRC and Uganda.

6. Rainfall Patterns: Last 90 Days During the past 90 days, rainfall was above average over most areas in the Sahel and the Gulf of Guinea region. Rainfall was also above average over part of central Africa, mainly southern Chad, western CAR, and southern Cameroon. Rainfall was also above average over western Ethiopia.

7. Rainfall Patterns: Last 180 Days During the past 180 days, rainfall was above average over much of West Africa, portions of central Africa, the Greater Horn of Africa, and parts of southern Africa. The exceptions were local areas in northern Nigeria, southern Tanzania, and northern Madagascar, which registered below average rainfall.

8. Recent Rainfall Evolution Daily evolution of precipitation during the last 90 days at selected regions indicates above average rainfall in the Groundnut basin of Senegal despite a few dry spells (lower panel – left). Rainfall deficits were significantly reduced over southwestern Nigeria as a result of frequent rains during the past week (bottom panel – right). Rainfall continued to be above average over western Ethiopia (upper panel – right).

9. Atmospheric Circulation:Last 7 Days The 850 hPa wind anomaly (left panel) reflected westerly wind anomalies across the eastern. The easterly wind anomaly over the central Sahel is evidence of an active African Easterly Jet (AEJ) conducive to enhanced rainfall. The 200 hPa wind anomaly (right panel) featured a northern hemisphere deep upper level trough extending into tropical Africa providing additional favorable conditions for enhanced rainfall activity.

10. NCEP GEFS Model ForecastsNon-Bias Corrected Probability of precipitation exceedance Week-1: Valid 17 - 23 August, 2010Week-2: Valid 24 – 30 August, 2010 For week-1, there is a high chance for precipitation to exceed 50 mm over Guinea-Bissau, parts of Guinea Conakry, Sierra Leone, parts of southern Nigeria and Cameroon. There is also a high chance for rainfall to exceed 50 mm over western Ethiopia. For week-2, there is a high chance for precipitation to exceed 50 mm over Guinea and parts of western Ethiopia.

11. Experimental Week-1 Precipitation Outlooks Week-1 Outlook 17 - 23 August, 2010 • There is an increased chance for above average precipitation over the western sector of the Sahel: The stronger than normal lower tropospheric flow from the Atlantic Ocean and its associated convergence over the western parts of the Sahel region are expected to enhance rainfall in the region. • Confidence: Moderate • 2. There is an increased chance for above average rainfall over western Ethiopia:The above average equatorial flow from the southwest Indian Ocean and the deep thermal low in the vicinity of the Gulf of Aden are expected to enhance rainfall in the region. • Confidence: Moderate

12. Experimental Week-2 Precipitation Outlooks Week-2 Outlook 24 –30 August, 2010 No forecast – Climatology suggested.

13. Summary During the past seven days, moderate to heavy rains fell across most areas in the Sahel. Areas that registered above average precipitation included portions of southern Niger, the western sectors of Burkina Faso and Mali, southern Mauritania, as well as northern and central Senegal, The Gambia, and Guinea Bissau. Rainfall was also above average over portions of the northern areas of the Gulf of Guinea region from Benin to Cote d’Ivoire, as well southern and western Nigeria. Rainfall was locally below average over Sierra Leone and southern Guinea. The northern part of central Africa, including southern Chad, and northern Ethiopia received above average rainfall. During the past 30 days, rainfall was highly above average over most areas in the Sahel from Niger to southern Mauritania and eastern Senegal. A few exceptions included western Niger, which registered slightly below average rainfall. In contrast, rainfall was below average over the Gulf of Guinea region, except of southern Nigeria, where rainfall was above average. In central Africa, rainfall was above average over the southern half f Chad and CAR. Rainfall was also above average over northern Ethiopia. Rainfall was below average over most portions of DRC and Uganda. During the past 90 days, rainfall was above average over most areas in the Sahel and the Gulf of Guinea region. Rainfall was also above average over part of central Africa, mainly southern Chad, western CAR, and southern Cameroon. Rainfall was also above average over western Ethiopia. For week-1, there is an increased chance for above average rainfall over the western areas of the Sahel and Ethiopia.