The African Monsoon Recent Evolution and Current Status Include Week-1 and Week-2 Outlooks

1. The African Monsoon Recent Evolution and Current StatusInclude Week-1 and Week-2 Outlooks Update prepared by Climate Prediction Center / NCEP 16 May 2011 For more information, visit: http://www.cpc.ncep.noaa.gov/products/Global_Monsoons/African_Monsoons/precip_monitoring.shtml

2. Outline • Highlights • Recent Evolution and Current Conditions • NCEP GEFS Forecasts • Summary

3. Highlights:Last 7 Days • Heavy rains resulted in moisture surpluses in CAR and parts of the Gulf of Guinea region. Local areas in the Sahel, including southern Mali and northern Burkina Faso received moderate to heavy rains as the Intertropical Convergence Zone (ITCZ) continues its northward progression. • Week-1 outlooks call for an increased chance for above average rainfall over much of the Gulf of Guinea countries, coastal central Africa, and portions of eastern Africa. There is an increased chance for below average rainfall over southern Sudan, northeastern DRC, and northern Uganda.

4. Rainfall Patterns: Last 7 Days During the past seven days, rainfall was below average over much of the Greater Horn of Africa, except for local areas in southwestern Ethiopia and southern Sudan, where rainfall was 25-50 mm above average. Rainfall was also above average over much of CAR, northwestern DRC, and northern Congo. However, rainfall was slightly below average over portions of the Congo sub-region, northern Cameroon, and southeastern Nigeria. Moderate to heavy rains soaked areas along the Gulf of Guinea coast, resulting in above average rainfall in local areas in Benin and Togo, southern Ghana, portions of Cote d’Ivoire, Liberia, and eastern Guinea. The rains extended northward to southern Mali and the area along the border with Burkina Faso.

5. Rainfall Patterns: Last 30 Days During the past 30 days, rainfall was above average over the southern sector of southern Africa in the areas including eastern South Africa, Namibia, southwestern Angola, and portions of Botswana. Rainfall was also above average along coastal Tanzania, parts of eastern Ethiopia, and local areas in the Gulf of Guinea region and the southern Sahel. Rainfall was below average over most areas in the Greater Horn of Africa and central Africa, including Nigeria.

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

7. 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 south 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.

8. 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).

9. Atmospheric Circulation:Last 7 Days The 850 hPa wind anomaly (left panel) featured a stronger than normal Somali Jet along coast eastern Africa and evidence of an easterly wind anomaly north of Lake Victoria. This resulted in an anomalous divergence pattern conducive of the rainfall deficits in this region. Westerly wind anomalies in the eastern sector of the Atlantic and easterly wind anomalies west of Lake Victoria might have resulted in the rainfall increase in the Gulf of Guinea and CAR, respectively. The 200 hPA wind anomaly (right panel) featured a north-south anomalous anticyclonic/cyclonic couplet and an anomalous anticyclonic flow over the tropical Atlantic. This pattern might have contributed to extending the moisture in the Gulf of Guinea into the southern areas of the Sahel.

10. NCEP GEFS Model ForecastsNon-Bias Corrected Probability of precipitation exceedance Week-1: Valid 17 – 23 May 2011Week-2: Valid 24 – 30 May 2011 For week-1 (left panel), there is a increased chance for rainfall to exceed 50mm over Gabon and portions of western Ethiopia and central Somalia. For week-2 (right panel), there is an increased chance for rainfall to exceed 50 mm over portions of central Africa, including Congo, Cameroon, and Gabon.

11. Experimental Week-1 Precipitation Outlooks • There is an increased chance for above average rainfall over much of the Gulf of Guinea countries: The combination of a weak but active phase of the MJO and Interactions between mid-latitude and tropical systems are expected to enhance rainfall in the region.Confidence: Moderate • There is an increased chance for below average rainfall over parts of coastal central Africa: The combination of the active phase of the MJO and lower tropospheric easterly anomalies from the moist Congo Air Boundary (CAB) area are expected to enhance rainfall in the region. Confidence: Moderate • There is an increased chance for below average rainfall over southern Sudan, northeastern DRC and northern Uganda: The phase of the MJO and anomalous lower tropospheric wind divergence are expected to suppress rainfall in the region. Confidence: Moderate • There is an increased chance for above average rainfall over southern and southeast Ethiopia, and northern Somalia: Anomalous easterlies from the Indian Ocean and their associated convergence across the Horn of Africa are expected to enhance rainfall in the region. Confidence: Moderate Week-1 Outlook 17 - 23 May, 2011

12. Experimental Week-2 Precipitation Outlooks Week-2 Outlook 24 – 30 May, 2011 No forecast

13. Summary During the past seven days, rainfall was below average over much of the Greater Horn of Africa, except for local areas in southwestern Ethiopia and southern Sudan, where rainfall was 25-50 mm above average. Rainfall was also above average over much of CAR, northwestern DRC, and northern Congo. However, rainfall was slightly below average over portions of the Congo sub-region, northern Cameroon, and southeastern Nigeria. Moderate to heavy rains soaked areas along the Gulf of Guinea coast, resulting in above average rainfall in local areas in Benin and Togo, southern Ghana, portions of Cote d’Ivoire, Liberia, and eastern Guinea. The rains extended northward to southern Mali and the area along the border with Burkina Faso. During the past 30 days, rainfall was above average over the southern sector of southern Africa in the areas including eastern South Africa, Namibia, southwestern Angola, and portions of Botswana. Rainfall was also above average along coastal Tanzania, parts of eastern Ethiopia, and local areas in the Gulf of Guinea region and the southern Sahel. Rainfall was below average over most areas in the Greater Horn of Africa and central Africa, including Nigeria. During the past 90 days, rainfall was above average over southern Angola, northern Namibia, southern Tanzania, and much of Madagascar. However, rainfall was below average over eastern Zimbabwe and southern Mozambique. The Greater Horn of Africa in the areas including Ethiopia, southern Sudan, the northern areas of Kenya and Uganda, and southern Somalia received below average rainfall. Rainfall was above average along coastal Gabon, Equatorial Guinea, and parts of the Gulf of Guinea region. Week-1 outlooks call for an increased chance for above average rainfall over much of the Gulf of Guinea countries, coastal central Africa, and portions of eastern Africa. There is an increased chance for below average rainfall over southern Sudan, northeastern DRC, and northern Uganda.