The African Monsoon Recent Evolution and Current Status Update prepared by Climate Prediction Center / NCEP 09 AUGUST 2010 For more information, visit:

Outline Highlights Recent Evolution and Current Conditions NCEP GEFS Forecasts Summary

Highlights: Last 7 Days Moderate to heavy rains soaked the northern areas of central Africa. Rainfall was also above average in climatologically drier regions of northern Sahel, including southwestern Mauritania and northern Mali. Most areas in the Gulf of Guinea region registered below average rainfall.

Rainfall Patterns: Last 7 Days During the past seven days, in the Sahel, rainfall was above average locally over southwestern Mauritania, northern Mali, parts of southern Niger. Rainfall was below average over most areas in the Gulf of Guinea region, except for western Guinea. Rainfall was above average over the northern areas of central Africa, central Sudan, and western Ethiopia. Rainfall was below average over southern Sudan.

Rainfall Patterns: Last 30 Days During the past 30 days, rainfall was above average over eastern Senegal, Southern tip of Mauritania, Guinea Conakry, Guinea Bissau, most parts of Mali, central and eastern parts of Cote d’Ivoire, northern Burkina Faso and central Nigeria. Rainfall was below average over Ghana, western Cote d’Ivoire and parts of Northern Nigeria. Meanwhile, in east Africa, rainfall was above average over southern half of Chad, most parts of CAR, western parts of DRC, southern Sudan, central and western Ethiopia. It was below average over western parts of Cameroon, eastern parts of DRC and most parts of Uganda. The seasonal dry weather condition has persisted in southern Africa including Madagascar.

Rainfall Patterns: Last 90 Days During the past 90 days, southeastern Senegal and Guinea, Liberia and Cote d’Ivoire, southern tip of Mali, Burkina Faso, and central Nigeria recieved above average rainfall. Rainfall was below average over parts of northern and western Nigeria. In central Africa, rainfall was above average over southern Chad, much of CAR, including, Cameroon and northern Congo. In eastern Africa, rainfall was above average over north and central Ethiopia and localized areas in Kenya.

Rainfall Patterns: Last 180 Days During the past 180 days, rainfall was above average along the Gulf of Guinea, much of central and eastern Africa, especially central Ethiopia and parts of southern Africa. However, parts of Nigeria, Tanzania and most parts of Madagascar had below average rainfall.

Recent Rainfall Evolution Daily evolution of precipitation during the last 90 days at selected regions indicated frequent rainfall events over part of Nigeria (lower panel – left). ). Despite steady rainfall, seasonal amounts have been below average over parts of southern Sudan (lower panel – right). The seasonal rainfall continued to be above average in parts of Ethiopia (upper panel – right).

Atmospheric Circulation: Last 7 Days The 850 hPa wind anomaly (left panel) reflected westerly wind anomalies across tropical eastern Atlantic into West Africa providing favorable conditions fro moisture to penetrate into West Africa. Southwesterly wind anomalies were also observed across the tropical Indian Ocean, indicating a strengthening of the Somali jet which feeds into the Indian monsoon. The 200 hPa wind anomaly (right panel) featured anomalous upper level cyclonic circulation across northern Atlantic, Europe and Asia, which act to suppress rainfall in the monsoon regions.

NCEP GEFS Model Forecasts Non-Bias Corrected Probability of precipitation exceedance Week-1: Valid 10 – 16 August, 2010 Week-2: Valid 17 – 23 August, 2010 For week-1, there is an increased chance for precipitation to exceed 50 mm over southern Mali, Guinea, Liberia, Sierra Leone, Burkina Faso, Togo, Benin, Nigeria, southern Chad, Central African Republic, northern DRC and western Ethiopia. For week-2, there is an increased chance for precipitation to exceed 50 mm over parts of the Gulf of Guinea region and western Ethiopia.

1. There is an increased chance for above average precipitation over many parts of the Sahel region: The interactions between mid-latitude frontal systems and low level tropical disturbances are expected to enhance rainfall in the region. Confidence: Moderate 2. There is an increased chance for above average rainfall over the western Ethiopia: The strong cross 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 Experimental Week-1 Precipitation Outlooks Week-1 Outlook August, 2010

Experimental Week-2 Precipitation Outlooks Week-2 Outlook 17 – 23 August, 2010 No forecast – Climatology suggested.

Summary During the past seven days, in the Sahel, rainfall was above average locally over southwestern Mauritania, northern Mali, parts of southern Niger. Rainfall was below average over most areas in the Gulf of Guinea region, except for western Guinea. Rainfall was above average over the northern areas of central Africa, central Sudan, and western Ethiopia. Rainfall was below average over southern Sudan During the past 30 days, rainfall was above average over eastern Senegal, Southern tip of Mauritania, Guinea Conakry, Guinea Bissau, most parts of Mali, central and eastern parts of Cote d’Ivoire, northern Burkina Faso and central Nigeria. Rainfall was below average over Ghana, western Cote d’Ivoire and parts of Northern Nigeria. Meanwhile, in east Africa, rainfall was above average over southern half of Chad, most parts of CAR, western parts of DRC, southern Sudan, central and western Ethiopia. It was below average over western parts of Cameroon, eastern parts of DRC and most parts of Uganda. The seasonal dry weather condition has persisted in southern Africa including Madagascar. During the past 90 days, southeastern Senegal and Guinea, Liberia and Cote d’Ivoire, southern tip of Mali, Burkina Faso, and central Nigeria had above average rainfall. Rainfall was below average over parts of northern and western Nigeria. In central Africa, rainfall was above average over southern Chad, much of CAR, including, Cameroon and northern Congo. In east Africa, rainfall was above average over north and central Ethiopia and localized areas of Kenya. For week-1, there is an increased chance for above average precipitation across most areas in the Sahel and western Ethiopia.