The African Monsoon Recent Evolution and Current Status Include Week-1 and Week-2 Outlooks Update prepared by Climate Prediction Center / NCEP 31 May 2011 For more information, visit:

Outline Highlights Recent Evolution and Current Conditions NCEP GEFS Forecasts Summary

Highlights: Last 7 Days Heavy rains continued to pound northern Ethiopia and local flooding may have persisted in this area. Central Sudan also received sizable rainfall amounts. Week-1 outlooks call for an increased chance for above average rainfall over the eastern sector of the Gulf of Guinea Region. There is an increased chance for below average rainfall over southern Sudan.

Rainfall Patterns: Last 7 Days During the past seven days, moderate to heavy rains sustained moisture surpluses over portions of northern and central Ethiopia. Rainfall was also above average over central Sudan. Rainfall was slightly below average along coastal central Africa. However, moderate to heavy rains resulted in moisture surpluses in local areas over the southern areas of Chad and CAR, and the northern sectors of DRC and Congo. Rainfall was also above average over local areas in the central part of the Gulf of Guinea region. However light rains resulted in below average moisture along the west coast.

Rainfall Patterns: Last 30 Days During the past 30 days, rainfall was above average over eastern Ethiopia, parts of Somalia, and northern Uganda. In contrast, rainfall was below average over southern Sudan and parts of Kenya, including the north and the east. Rainfall was below average over northern DRC, parts of southern Chad, northern Cameroon, and northern Nigeria. Rainfall was above average over local areas in the Gulf of Guinea region. Moderate rains resulted in moisture surpluses over much of Morocco.

Rainfall Patterns: Last 90 Days During the past 90 days, rainfall was above average over southern Angola, northern Namibia, western Botswana, western Zambia, southern Tanzania, and parts of Madagascar. However, rainfall was below average over eastern Zimbabwe and southern Mozambique. The Greater Horn of Africa in the areas including southern Ethiopia, southern Sudan, the northern areas of Kenya and Uganda, and southern Somalia received below average rainfall. Rainfall was also below average over much of central Africa, except for coastal Gabon and Equatorial Guinea. Rainfall was also above average over parts of the Gulf of Guinea region.

Rainfall Patterns: Last 180 Days During the past 180 days, rainfall was above average over much of southern Africa from central Angola and northern Zambia southward and eastward to South Africa and Madagascar. Rainfall was below average over the Greater Horn of Africa and the northern part of central Africa. Rainfall was above average along coastal central Africa and Gulf of Guinea.

Recent Rainfall Evolution Daily evolution of rainfall over the last 90 days at selected stations indicates that persistent rains over the past several weeks resulted in moisture surpluses over central Cote d’Ivoire (bottom panel – left). Despite significant moisture deficits in many parts of Kenya, the country’s breadbasket in the southwest registered moisture surpluses (bottom panel – right ). Daily rains over the past several weeks increased moisture surpluses in southwestern Ethiopia (upper panel – right).

Atmospheric Circulation: Last 7 Days The 850 hPa wind anomaly (left panel) featured a wave pattern over northern Africa associated with the rains over northern Africa. An anomalous cyclonic circulation over the Gulf of Guinea, which may have contributed to the rainfall increase in local areas in this region. Southeasterlies across the Indian Ocean turning into northwesterlies over the Horn of Africa contributed to the above average rainfall observed over Ethiopia. The 200 hPA wind anomaly (right panel) featured anomalous cyclonic couplets over northern Africa. An anomalous northerly flow into the Horn of Africa is present and may have acted to sustain the rains in Ethiopia.

NCEP GEFS Model Forecasts Non-Bias Corrected Probability of precipitation exceedance Week-1: Valid 31 May – 06 June 2011 Week-2: Valid 07 – 13 June 2011 For week-1 (left panel) and week-2 (right panel), there is an increased chance for rainfall to exceed 50mm over along the Gulf of Guinea coast and parts of western Ethiopia.

Experimental Week-1 Precipitation Outlooks Week-1 Outlook 31 May – 06 June There is an increased chance for above average rainfall over the eastern sector of the Gulf of Guinea Region: Anomalous moist easterlies from eastern Africa and their associated convergence across western equatorial Africa are expected to enhance rainfall in this region. Confidence: Moderate 2.There is an increased chance for below average rainfall over southern Sudan: Anomalous lower tropospheric divergence is expected to suppress rainfall in this region. Confidence: Moderate

Experimental Week-2 Precipitation Outlooks Week-2 Outlook 07 – 13 June, 2011 No forecast

Summary During the past seven days, moderate to heavy rains sustained moisture surpluses over portions of northern and central Ethiopia. Rainfall was also above average over central Sudan. Rainfall was slightly below average along coastal central Africa. However, moderate to heavy rains resulted in moisture surpluses in local areas over the southern areas of Chad and CAR, and the northern sectors of DRC and Congo. Rainfall was also above average over local areas in the central part of the Gulf of Guinea region. However light rains resulted in below average moisture along the west coast. During the past 30 days, rainfall was above average over eastern Ethiopia, parts of Somalia, and northern Uganda. In contrast, rainfall was below average over southern Sudan and parts of Kenya, including the north and the east. Rainfall was below average over northern DRC, parts of southern Chad, northern Cameroon, and northern Nigeria. Rainfall was above average over local areas in the Gulf of Guinea region. Moderate rains resulted in moisture surpluses over much of Morocco. During the past 90 days, rainfall was above average over southern Angola, northern Namibia, western Botswana, western Zambia, southern Tanzania, and parts of Madagascar. However, rainfall was below average over eastern Zimbabwe and southern Mozambique. The Greater Horn of Africa in the areas including southern Ethiopia, southern Sudan, the northern areas of Kenya and Uganda, and southern Somalia received below average rainfall. Rainfall was also below average over much of central Africa, except for coastal Gabon and Equatorial Guinea. Rainfall was also above average over parts of the Gulf of Guinea region. Week-1 outlooks call for an increased chance for above average rainfall over the eastern sector of the Gulf of Guinea Region. There is an increased chance for below average rainfall over southern Sudan.