The African Monsoon Recent Evolution and Current Status Include Week-1 and Week-2 Outlooks Update prepared by Climate Prediction Center / NCEP 19 September 2011 For more information, visit:

Outline Highlights Recent Evolution and Current Conditions NCEP GEFS Forecasts Summary

Highlights: Last 7 Days Heavy rainfall in excess of 160mm was observed over local areas of central Mali and southwestern Cameroon. Week-1 outlooks call for an increased chance for above average rainfall over western Equatorial African countries, while suppressed rainfall is expected to prevail over South Sudan and the neighboring areas of East Africa.

Rainfall Patterns: Last 7 Days During the past seven days, southern and central Mali, eastern Burkina Faso, local areas of Guinea, Cote D’Ivoire and Ghana, portions of Togo and Benin, northern Nigeria, southern Niger, much of Cameroon, portions of Chad, western CAR, northern Congo Brazzaville, northern and eastern DRC, Rwanda, parts of Uganda, and local areas of eastern Sudan received above average rainfall. Below average rainfall prevailed over central and southern Nigeria, eastern CAR and portions of Ethiopia.

Rainfall Patterns: Last 30 Days During the past 30 days, southern Senegal, Guinea Bissau, northern Guinea, western and central Mali, eastern Burkina Faso, northern Ghana, northern Togo, northern Benin, local areas of Nigeria, portions of Niger, southern Chad, western CAR, southern Cameroon, northern Congo Brazzaville, much of South Sudan, Uganda, Rwanda and western Kenya received above average rainfall. In contrast, rainfall was below average over many places of the Gulf of Guinea countries, parts of CAR, southern DRC, eastern Sudan, Eritrea and portions of Ethiopia.

Rainfall Patterns: Last 90 Days During the past 90 days, coastal West Africa, many parts of Nigeria, local areas of Cameroon, eastern Sudan and portions of Ethiopia received below average rainfall. Moisture surpluses were observed across the Senegal-Mali-Guinea border, southwestern and central Mali, eastern Burkina Faso, eastern Ghana, parts of Chad and CAR, northern Congo Brazzaville, Uganda and western Kenya.

Rainfall Patterns: Last 180 Days During the past 180 days, rainfall was below average over coastal West Africa, much of Nigeria, portions of Cameroon, Equatorial Guinea, eastern Gabon, southern and central Congo Brazzaville, western and northern DRC, eastern CAR, portion of South Sudan Republic, eastern Sudan, Ethiopia, Eritrea, portions of Kenya and southern Somalia. Moisture surpluses were observed, over northern Guinea Conakry, parts of southern and central Mali, local areas of Chad and CAR, northern Congo Brazzaville, Uganda, parts of southern Tanzania, southern Angola, northern Namibia, portions of Madagascar and local areas of South Africa.

Recent Rainfall Evolution Daily evolution of rainfall over the last 90 days at selected stations reflects moisture deficits that prevailed over parts of southern Mauritania (bottom panel – left), western Niger (bottom panel- right) and eastern Sudan (top panel – right).

Atmospheric Circulation: Last 7 Days The 850hPa wind anomaly (left panel) featured strong westerly anomalies across the Gulf of Guinea and the adjoining areas of the Atlantic Ocean. These westerly anomalies with their associated convergences may have contributed to the heavy rainfall event over southwestern Cameroon. The 200hpa wind anomaly (right panel) featured anomalous easterlies across northern Africa and anticyclonic anomalies over southern Atlantic Ocean and southwest Indian Ocean.

NCEP GEFS Model Forecasts Non-Bias Corrected Probability of precipitation exceedance Week-1: Valid 20 – 26 September 2011 Week-2: Valid 27 September – 03 October 2011 For week-1 (left panel) and week-2 (right panel), there is an increased chance for rainfall to exceed 50 mm over coastal Gulf of Guinea, and western and central parts of Equatorial African countries.

Experimental Week-1 Precipitation Outlooks Week-1 Outlook 20 – 26 September There is an increased chance for above average precipitation over southern Cameroon, Equatorial Guinea, Gabon, southwestern CAR, Congo Brazzaville and western DRC: Anomalous wind convergence between westerlies from the Atlantic Ocean and easterlies from the Congo Air Boundary (CAB) area is expected to enhance rainfall in the region. Confidence: Moderate 2.There is an increased chance for below average precipitation over central southern Sudan, eastern CAR, northeastern DRC, northern Uganda, northwestern Kenya and southwestern Ethiopia: Anomalous lower tropospheric divergence is expected to suppress rainfall in the region. Confidence: Moderate

Experimental Week-2 Precipitation Outlooks Week-2 Outlook 27 September – 03 October 2011 No forecast

Summary During the past seven days, southern and central Mali, eastern Burkina Faso, local areas of Guinea, Cote D’Ivoire and Ghana, portions of Togo and Benin, northern Nigeria, southern Niger, much of Cameroon, portions of Chad, western CAR, northern Congo Brazzaville, northern and eastern DRC, Rwanda, parts of Uganda, and local areas of eastern Sudan received above average rainfall. Below average rainfall prevailed over central and southern Nigeria, eastern CAR and portions of Ethiopia. During the past 30 days, southern Senegal, Guinea Bissau, northern Guinea, western and central Mali, eastern Burkina Faso, northern Ghana, northern Togo, northern Benin, local areas of Nigeria, portions of Niger, southern Chad, western CAR, southern Cameroon, northern Congo Brazzaville, much of South Sudan, Uganda, Rwanda and western Kenya received above average rainfall. In contrast, rainfall was below average over many places of the Gulf of Guinea countries, parts of CAR, southern DRC, eastern Sudan, Eritrea and portions of Ethiopia. During the past 90 days, coastal West Africa, many parts of Nigeria, local areas of Cameroon, eastern Sudan and portions of Ethiopia received below average rainfall. Moisture surpluses were observed across the Senegal-Mali-Guinea border, southwestern and central Mali, eastern Burkina Faso, eastern Ghana, parts of Chad and CAR, northern Congo Brazzaville, Uganda and western Kenya. Week-1 outlooks call for an increased chance for above average rainfall over western Equatorial African countries, while suppressed rainfall is expected to prevail over South Sudan and the neighboring areas of East Africa.