The African Monsoon Recent Evolution and Current Status Update prepared by Climate Prediction Center / NCEP 26 May 2009 For more information, visit:

Outline Highlights Recent Evolution and Current Conditions NCEP GEFS Forecasts Summary

Highlights: Last 7 Days Moderate to heavy rains continued to benefit many areas in Uganda, while in Kenya the rains were confined to local areas in the southwest. Light rains sustained moisture deficits over parts of southern Sudan, Ethiopia, and CAR. Rainfall continued to diminish in the Gulf of Guinea region of West Africa.

Rainfall Patterns: Last 7 Days During the past week, moderate rains fell over portions of southwestern Kenya and continue to bring relief in local areas. Much of the country was dry however as the rainy season has begun to wind down. Moderate to heavy rains also continued to help reduce seasonal moisture deficits over most areas in Uganda. Except for heavy downpours in local areas in southwestern Sudan, rainfall was below average over most areas in southern Sudan and the central African countries, including CAR, parts of Cameroon, northern Gabon, and local areas in DRC. Rainfall was also below average over most areas in the Gulf of Guinea region and the southern areas of the Sahel.

Rainfall Patterns: Last 30 Days During the last 30 days, light rains sustained moisture deficits in central Kenya, most areas in central and eastern Ethiopia, and southern Sudan. Rainfall also below average over parts of eastern CAR, northern Cameroon, and northern Gabon. Rainfall was above average over most areas in western DRC, Congo, and southern Gabon. In West Africa, rainfall was below average over northern Nigeria, and in local areas over Benin, Togo, and Ghana. Rainfall was also below average over parts of Liberia and Sierra Leone. The southern areas of the Sahel registered slightly above average rainfall.

Rainfall Patterns: Last 90 Days During the past 90 days, rainfall was below average over central Ethiopia, parts of western Kenya, and northern Uganda. Rainfall was also below average over northern Angola, parts of eastern Zambia, eastern Zimbabwe, and parts of central and southern Mozambique, and much of Madagascar. In contrast, rainfall was above average over parts of southwestern Angola, northwestern Namibia, and eastern South Africa. Rainfall was also above average locally over southeastern CAR, parts of the northern areas of Congo and DRC, and coastal Cameroon.

Rainfall Patterns: Last 180 Days Over the past 180 days, rainfall was above average across most areas in continental southern Africa. Rainfall was below average along the northwest coast of Madagascar, northern Angola, southern and central DRC. Rainfall was also below average over most areas in Kenya and parts of southern Ethiopia. In central Africa, rainfall was above average over local areas in northern Congo, coastal Cameroon, and parts of the Gulf of Guinea region in West Africa.

Recent Rainfall Evolution Daily rainfall evolution during the last 90 days shows that rainfall continued to diminish in parts of the Gulf of Guinea region over the past week (bottom left) erasing the moisture surpluses accummulated over the past 90 days. Overall light rains sustained moisture deficits over southern Kenya (bottom right). A wet spell parts of southern Ethiopia contributed to some moisture recovery in this area (top right).

Atmospheric Circulation: Last 7 Days Over the past 7 days, the 850 hPa wind anomaly (left panel) featured an anomalous ridge from the Mediterranean Sea into to northern Africa. Easterly wind anomalies extended from West Africa into the Atlantic Ocean. A strong southerly cross equatorial flow extended from the southern Indian Ocean into the Horn of Africa. The 200 hPa wind anomaly (right panel) featured an anomalous cyclonic/anticyclonic couplet over northern Africa.

NCEP GEFS Model Forecasts Non-Bias Corrected Probability of precipitation exceedance Week-1: Valid June, 2009 Week-2: Valid June, 2009 For week-1 and week-2, the global ensemble forecast system (GEFS) suggests over 90% chance for precipitation to exceed 50 mm over local areas in southern Cameroon, northern Gabon.

Experimental Week-1 Precipitation Outlooks Week-1 Outlook 26 May – 1 June, An increased chance for below average rainfall over southern Sudan and western Ethiopia. A cross equatorial flow from the south Indian Ocean into the northern Indian Ocean is expected to divert moisture away from this region. Confidence: Moderate

Experimental Week-2 Precipitation Outlooks Week-2 Outlook June 2009 No Forecast

Summary During the past week, moderate rains fell over portions of southwestern Kenya and continue to bring relief in local areas. Much of the country was dry however as the rainy season has begun to wind down. Moderate to heavy rains also continued to help reduce seasonal moisture deficits over most areas in Uganda. Except for heavy downpours in local areas in southwestern Sudan, rainfall was below average over most areas in southern Sudan and the central African countries, including CAR, parts of Cameroon, northern Gabon, and local areas in DRC. Rainfall was also below average over most areas in the Gulf of Guinea region and the southern areas of the Sahel. During the last 30 days, light rains sustained moisture deficits in central Kenya, most areas in central and eastern Ethiopia, and southern Sudan. Rainfall also below average over parts of eastern CAR, northern Cameroon, and northern Gabon. Rainfall was above average over most areas in western DRC, Congo, and southern Gabon. In West Africa, rainfall was below average over northern Nigeria, and in local areas over Benin, Togo, and Ghana. Rainfall was also below average over parts of Liberia and Sierra Leone. The southern areas of the Sahel registered slightly above average rainfall.. For week-1 valid 26 May – 1 June 2009, there is an increased chance for below average rainfall over the southern areas of Sudan and eastern CAR. There is no confidence in the forecast for week-2.