The African Monsoon Recent Evolution and Current Status Include Week-1 and Week-2 Outlooks Update prepared by Climate Prediction Center / NCEP 24 August 2015 For more information, visit:

Outline Highlights Recent Evolution and Current Conditions NCEP GEFS Forecasts Summary

Highlights: Last 7 Days Weekly total rainfall exceeded 150mm over western Guinea, Senegal and southern Mali. Locally heavy rainfall was also observed over western Ethiopia, southern Chad and southern Sudan. Week-1 outlooks call for an increased chance for above-average rainfall over southern Mali, Burkina Faso, western Niger, northwestern Nigeria, as well as, throughout portions of Chad, Sudan and western Ethiopia. In contrast, there is an increased chance for below-average rainfall throughout several Gulf of Guinea countries including Guinea, Sierra Leone, Cote d'Ivoire, Ghana, Togo and Benin.

Rainfall Patterns: Last 7 Days During the past seven days, above-average rainfall was received across western Senegal, northern Guinea, Mali, Burkina Faso and southeastern Niger. As much as 100mm of accumulated rainfall was observed over western Senegal and northern Guinea and southern Mali. In contrast, portions of southern Guinea, Liberia, Sierra Leon, northern Nigeria, southern Chad South Sudan, and western Ethiopia mainly saw a suppression of seasonal rainfall during the last seven days.

Rainfall Patterns: Last 30 Days During the past 30 days, rainfall was above-average over portions of Mauritania, Senegal, Gambia, much of Mali, Guinea-Bissau, Guinea-Conakry, Sierra Leone, local areas in Liberia, northern Ghana, Burkina Faso, northern Togo, northern Benin, portions of Nigeria, Niger, Cameroon, western CAR, southern Chad, portions of Sudan and South Sudan Republic, local areas in DRC and portions of Ethiopia. In contrast, below-average rainfall was observed over much of Cote d’Ivoire, southern Ghana, southern Togo, southern Benin, portions of Nigeria, local areas in Cameroon and Congo-Brazzaville, portions of central Chad, eastern CAR western South Sudan Republic, and northeastern Ethiopia.

Rainfall Patterns: Last 90 Days During the past 90 days, rainfall was above-average over southern Mauritania, much of Mali, Senegal, Guinea-Conakry, Sierra Leone, Liberia, portions of Cote d’Ivoire, Burkina Faso, Niger, southern Chad, portions of Cameroon, CAR, South Sudan Republic, southern Sudan, portions of DRC, Uganda, many parts of Ethiopia, and parts of northern Somalia. In contrast, local areas in Cote d’Ivoire, Ghana, Togo, Benin, Nigeria, southern Cameroon, eastern Gabon, Congo Brazzaville, eastern Chad, southern Sudan, portions of DRC, Eritrea, and local areas in Ethiopia and Eritrea.

Rainfall Patterns: Last 180 Days During the past 180 days, rainfall was above-average over much of Senegal, southern Mauritania, much of Guinea, Guinea-Bissau, Sierra Leone, Liberia, Mali, Burkina Faso, Cote d’Ivoire, Niger, portions of Chad, many parts of CAR, local areas in Gabon, northern Congo-Brazzaville, much of DRC, South Sudan Republic, southern Sudan, Somalia, portions of Ethiopia, Zambia, northern Mozambique, portions of Botswana and Zimbabwe, and Madagascar. In contrast, portions of Ghana, southern Togo, southern Benin, much of Nigeria, portions of Cameroon, Angola, Namibia, northern South Africa, southern and central Mozambique, Malawi, portions of Tanzania, local areas in DRC, northern Kenya and portions of Ethiopia had below-average rainfall.

Recent Rainfall Evolution Daily evolution of rainfall over the last 90 days at selected locations show that moderate to heavy rainfall sustained moisture surpluses over portions of eastern Senegal (bottom left), and helped to mitigate accumulated rainfall deficits over parts of southwestern Niger (bottom right). In contrast, low seasonal total rainfall increased moisture deficits over portions of northeastern Ethiopia (top right).

Atmospheric Circulation: Last 7 Days The 850hpa wind anomalies (left panel) featured westerlies across the Sahel region, and anomalous lower-level easterlies along the Gulf of Guinea coast, resulting in lower-level cyclonic shear across Guinea and the neighboring areas. This anomalous lower-level cyclonic shear, combined with anomalous upper-level divergent flow (right panel) may have contributed to the observed heavy rainfall in the region.

NCEP GEFS Model Forecasts Non-Bias Corrected Probability of precipitation exceedance Week-1: Valid 25– 31 Aug 2015 Week-2: Valid 1 – 7 Sep 2015 For week-1 (left panel) and week-2(right panel), there is an increased chance for rainfall to exceed 50 mm over portions southern Mali, western Niger, Burkina Faso, northern Nigeria, Cameroon, CAR, northern DRC and western Ethiopia.

Week-1 Precipitation Outlooks 26 Aug – 01 Sep, There is an increased chance for above-average rainfall across southern Mali, Burkina Faso, northern Benin, southwestern Niger, Nigeria, Cameroon, Chad, northern Burkina Faso, and western Sudan: A broad area of anomalous lower-level convergence and upper-level divergence is expected to enhance rainfall in the region. Confidence: Moderate 2.There is an increased chance for below-average rainfall across Liberia, Cote d’Ivoire, Ghana, Togo and Benin: Anomalous lower-level convergence is expected to suppress rainfall in the region. Confidence: Moderate

Week-2 Precipitation Outlooks 02 Sep – 08 Sep, There is an increased chance for above-average rainfall over southern Mauritania, Senegal, Gambia, Guinea- Bissau, Guinea, Sierra Leone, northern Liberia, northern Cote d’Ivoire, Mali, Burkina Faso, northern Benin, and southern Niger: A broad area of anomalous lower-level convergence and upper-level divergence is expected to enhance rainfall in the region. Confidence: Moderate

Summary During the past seven days, above-average rainfall was received across western Senegal, northern Guinea, Mali, Burkina Faso and southeastern Niger. As much as 100mm of accumulated rainfall was observed over western Senegal and northern Guinea and southern Mali. In contrast, portions of southern Guinea, Liberia, Sierra Leon, northern Nigeria, southern Chad South Sudan, and western Ethiopia mainly saw a suppression of seasonal rainfall during the last seven days. During the past 30 days, rainfall was above-average over portions of Mauritania, Senegal, Gambia, much of Mali, Guinea-Bissau, Guinea-Conakry, Sierra Leone, local areas in Liberia, northern Ghana, Burkina Faso, northern Togo, northern Benin, portions of Nigeria, Niger, Cameroon, western CAR, southern Chad, portions of Sudan and South Sudan Republic, local areas in DRC and portions of Ethiopia. In contrast, below-average rainfall was observed over much of Cote d’Ivoire, southern Ghana, southern Togo, southern Benin, portions of Nigeria, local areas in Cameroon and Congo-Brazzaville, portions of central Chad, eastern CAR western South Sudan Republic, and northeastern Ethiopia. During the past 90 days, rainfall was above-average over southern Mauritania, much of Mali, Senegal, Guinea-Conakry, Sierra Leone, Liberia, portions of Cote d’Ivoire, Burkina Faso, Niger, southern Chad, portions of Cameroon, CAR, South Sudan Republic, southern Sudan, portions of DRC, Uganda, many parts of Ethiopia, and parts of northern Somalia. In contrast, local areas in Cote d’Ivoire, Ghana, Togo, Benin, Nigeria, southern Cameroon, eastern Gabon, Congo Brazzaville, eastern Chad, southern Sudan, portions of DRC, Eritrea, and local areas in Ethiopia and Eritrea. Week-1 outlooks call for an increased chance for above-average rainfall over southern Mali, Burkina Faso, western Niger, northwestern Nigeria, as well as, throughout portions of Chad, Sudan and western Ethiopia. In contrast, there is an increased chance for below-average rainfall throughout several Gulf of Guinea countries including Ghana, Sierra Leone, Cote d’Ivoire, Ghana, Togo and Benin.