The African Monsoon Recent Evolution and Current Status Include Week-1 and Week-2 Outlooks

1. The African Monsoon Recent Evolution and Current StatusInclude Week-1 and Week-2 Outlooks Update prepared by Climate Prediction Center / NCEP 15 August 2011 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 • Summary

3. Highlights:Last 7 Days • Isolated heavy rainfall in excess of 120mm resulted in moisture surpluses across the Lake Chad region, northern Cameroon and western Kenya. • Week-1 outlooks call for an increased chance for above average rainfall over western parts of the Sahel Region, portions of central African countries and western Sudan.

4. Rainfall Patterns: Last 7 Days During the past seven days, rainfall was above average over local areas of eastern Mauritania, central Mali, northern Burkina Faso, western Niger, central and southern Chad, northern Cameroon, northern DRC, Uganda and western Kenya. On the other hand, below average rainfall prevailed over eastern Senegal, Gambia, Guinea Bissau, western Guinea, Sierra Leone, southern Mali, southern Burkina Faso, much of Nigeria, southern Cameroon, parts of CAR, southern Sudan, western and northern Ethiopia and western Eritrea.

5. Rainfall Patterns: Last 30 Days During the past 30 days, northern Burkina Faso and the neighboring areas of Mali, local areas of Ghana, the Lake Chad region, eastern Cameroon, CAR, southeastern Chad, southern Darfur region of Sudan, southern parts of South Sudan Republic, portions of Uganda and western Kenya received above average rainfall. In contrast, much of the rest of the Sahel, the Gulf of Guinea, and portions of central African countries, eastern Sudan and the neighboring areas of Ethiopia experienced rainfall deficits. Gauge rainfall observation of the National Meteorological Agency of Ethiopia indicated enhanced rainfall over parts of central Ethiopia.

6. Rainfall Patterns: Last 90 Days During the past 90 days, coastal West Africa, many places of Nigeria, parts of Cameroon and Gabon, northern DRC, eastern Sudan, and northwestern Ethiopia received below average rainfall. Localized moisture surpluses were observed over Ghana, coastal Nigeria, Lake Chad region, CAR, eastern Ethiopia, Uganda, western Kenya and coastal South Africa.

7. Rainfall Patterns: Last 180 Days During the past 180 days, rainfall was above average over southern Angola, northern Namibia, parts of South Africa, southern Tanzania and much of Madagascar. In contrast, below average rainfall was observed over central and southern Mozambique, eastern Zimbabwe, western and northern DRC, South Sudan, parts of Kenya, southern Somalia, portions of Ethiopia and eastern CAR. Much of Nigeria, costal Guinea, Sierra Leone, parts of Liberia, and local areas of western Niger also received below average rainfall, while rainfall was above average over parts of Ghana, eastern Cote D’Ivoire and local areas of CAR and the Lake Victoria region.

8. Recent Rainfall Evolution Daily evolution of rainfall over the last 90 days at selected stations reflects the continued suppressed rainfall over parts of Senegal (bottom panel – left) and western Niger (bottom panel-right). The recent rainfall events over southern Darfur region of Sudan helped to overcome seasonal rainfall deficits that had prevailed in the region (upper panel – right).

9. Atmospheric Circulation:Last 7 Days The 850hPa wind anomaly (left panel) featured anomalous northeasterly flow across East Africa, reflecting weaker than average Somali Jet across the region. The westerly anomalies across the Gulf of Guinea and central African region, with their cyclonic turning may have contributed to the observed heavy rainfall near Lake Chad and northern Cameroon. The 200hpa wind anomaly (right panel) featured anomalous cyclonic circulation across southern African countries and anomalous anticyclonic circulation over southeast Atlantic Ocean.

10. NCEP GEFS Model ForecastsNon-Bias Corrected Probability of precipitation exceedance Week-1: Valid 16 - 22 August 2011Week-2: Valid 23 - 29 August 2011 For week-1 (left panel) and week-2 (right panel) , there is an increased chance for rainfall to exceed 50 mm in the region between Senegal and western Sudan, across the Sahel countries. High probabilities for the 50mm threshold also include Cameroon, much of CAR, northern DRC, portions of South Sudan Republic and western Ethiopia.

11. Experimental Week-1 Precipitation Outlooks Week-1 Outlook 16 – 22 August 2011 • There is an increased chance for above average precipitation over eastern Senegal, Gambia, Guinea Bissau, Guinea, northern Cote d’Ivoire northern Ghana, southern and central Mali, southern Mauritania, Burkina Faso and western Niger: Anomalous westerlies from the Atlantic Ocean with their cyclonic turning over western Africa are expected to enhance rainfall in the region. Confidence: Moderate • There is an increased chance for above average precipitation portions of the central African countries and the neighboring areas of Sudan and South Sudan Republic: Anomalous southwesterly winds across the Gulf of Guinea and their associated convergence over central African area are expected to enhance rainfall in the region. Confidence: Moderate

12. Experimental Week-2 Precipitation Outlooks Week-2 Outlook 23 - 29 August, 2011 No forecast

13. Summary During the past seven days, rainfall was above average over local areas of eastern Mauritania, central Mali, northern Burkina Faso, western Niger, central and southern Chad, northern Cameroon, northern DRC, Uganda and western Kenya. On the other hand, below average rainfall prevailed over eastern Senegal, Gambia, Guinea Bissau, western Guinea, Sierra Leone, southern Mali, southern Burkina Faso, much of Nigeria, southern Cameroon, parts of CAR, southern Sudan, western and northern Ethiopia and western Eritrea. During the past 30 days, northern Burkina Faso and the neighboring areas of Mali, local areas of Ghana, the Lake Chad region, eastern Cameroon, CAR, southeastern Chad, southern Darfur region of Sudan, southern parts of South Sudan Republic, portions of Uganda and western Kenya received above average rainfall. In contrast, much of the rest of the Sahel, the Gulf of Guinea, and portions of central African countries, eastern Sudan and the neighboring areas of Ethiopia experienced rainfall deficits. Gauge rainfall observation of the National Meteorological Agency of Ethiopia indicated enhanced rainfall over parts of central Ethiopia. During the past 90 days, coastal West Africa, many places of Nigeria, parts of Cameroon and Gabon, northern DRC, eastern Sudan, and northwestern Ethiopia received below average rainfall. Localized moisture surpluses were observed over Ghana, coastal Nigeria, Lake Chad region, CAR, eastern Ethiopia, Uganda, western Kenya and coastal South Africa. Week-1 outlooks call for an increased chance for above average rainfall over western parts of the Sahel Region, portions of central African countries and western Sudan.