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 18 April 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 • Rainfall was locally extremely heavy over southwestern Ethiopia, parts of DRC, Congo, Gabon, CAR, Cote d’Ivoire, and Ghana, with surpluses ranging between 75 and 100 mm. • Week-1 outlooks call for an increased chance for Week-1 outlooks call for an increased chance for above average rainfall along the Gulf of Guinea coast and coastal central Africa. There is also an increased chance for above average rainfall over parts of Ethiopia, southern Sudan, northern Uganda and northern Kenya.

4. Rainfall Patterns: Last 7 Days During the past seven days, dry conditions prevailed in much of East Africa, except for local areas in southwestern Ethiopia, where heavy rains sustained moisture surpluses. Light or no rain fell in many parts of southern Africa as the withdrawal of the rainfall season continued. Dry conditions sustained moisture deficits over the northern half of southern Africa, including much of Madagascar, Mozambique, Malawi, Zambia, and Zimbabwe. Light or no rain brought relief to flooded areas along the western border between Namibia and Angola. Much of the rains occurred over central Africa. Above average rainfall was seen over the northern areas of DRC and Congo, Gabon, southern Cameroon, and much of CAR. Heavy rains sustained moisture surpluses along the Gulf of Guinea coast between Cote d’Ivoire and Benin.

5. Rainfall Patterns: Last 30 Days During the past 30 days, rainfall remained largely below-average over Zimbabwe and central Mozambique, with deficits exceeding 100 mm in local areas. Rainfall was also below average over parts of Madagascar, northeastern South Africa, southern Malawi, much of Zambia, northern Angola, and eastern Botswana. Rainfall was significantly above average over southwestern Angola and northwestern Namibia. Above average rainfall was also seen in in much of Tanzania. Below average moisture conditions were present over eastern Kenya, while the west, Uganda , parts of central Africa, and the Gulf of Guinea region received moisture surpluses.

6. Rainfall Patterns: Last 90 Days During the past 90 days, rainfall was above average over southern Angola, northern Namibia, the areas along the border between Tanzania and Mozambique, and much of Madagascar. However, rainfall was below average over the remainder areas of continental southeastern Africa. Eastern Kenya, southern Somalia received below average rainfall. Rainfall was also below average over southern DRC, central Congo, Gabon. Rainfall was above average over northern DRC, parts of CAR, southern Cameroon, and the area along the Gulf of Guinea coast.

7. Rainfall Patterns: Last 180 Days During the past 180 days, rainfall was above average over parts of southern Africa, including northern Namibia and southern Angola, and northern Madagascar. Rainfall was also above average over the Gulf of Guinea region. Moisture deficits were seen in DRC and in many areas in eastern Africa, including southern Ethiopia, eastern Kenya, and southern Somalia.

8. Recent Rainfall Evolution Daily evolution of rainfall over the last 90 days at selected stations indicates that steady rains brought relief to rainfall needed dryness prevailed in northwestern Namibia during the past week (lower panel – left). Rainfall returned to section of northeastern South Africa, but not enough to reduce moisture deficits (lower panel right). Consecutive wet and dry spells in southwestern Kenya resulted in cumulative near average rains (upper panel – right).

9. Atmospheric Circulation:Last 7 Days The 850 hPa wind anomaly (left panel) featured an anomalous cyclonic circulation centered over Madagascar, which produced very little rain in this area. Weak easterly wind anomalies also did not bring much needed rainfall over eastern Africa. Easterly wind anomalies from the Congo Air Boundary converged with westerlies from the eastern Atlantic sector to contribute to above average rainfall in parts of the Gulf of Guinea region. The 200 hPa wind anomaly map (right panel) revealed an upper level equatorial trough along the East Africa coast that might have contributed to the drynees in this region.

10. NCEP GEFS Model ForecastsNon-Bias Corrected Probability of precipitation exceedance Week-1: Valid 19 – 25 April 2011Week-2: Valid 26 – 02 May 2011 For week-1 and week-2, the high chance for rainfall to exceed 50 mm is confined to the areas alon coastal Tanzania, and Gabon.

11. Experimental Week-1 Precipitation Outlooks Week-1 Outlook 19 – 25 April, 2011 • There is an increased chance for above average rainfall along the Gulf of Guinea coast and coastal central Africa: Anomalous lower tropospheric winds from the Atlantic Ocean, and easterly anomalies from the moist Congo Air Boundary region are expected to enhance rainfall in this region. Confidence: Moderate • There is an increased chance for above average rainfall over parts of Ethiopia, southern Sudan, northern Uganda and northern Kenya: Interaction between mid-latitude and tropical weather systems across northeast Africa is expected to enhance rainfall in the region. Confidence: Moderate

12. Experimental Week-2 Precipitation Outlooks Week-2 Outlook 26 April – 02 May, 2011 No Forecast

13. Summary During the past seven days, dry conditions prevailed in much of East Africa, except for local areas in southwestern Ethiopia, where heavy rains sustained moisture surpluses. Light or no rain fell in many parts of southern Africa as the withdrawal of the rainfall season continued. Dry conditions sustained moisture deficits over the northern half of southern Africa, including much of Madagascar, Mozambique, Malawi, Zambia, and Zimbabwe. Light or no rain brought relief to flooded areas along the western border between Namibia and Angola. Much of the rains occurred over central Africa. Above average rainfall was seen over the northern areas of DRC and Congo, Gabon, southern Cameroon, and much of CAR. Heavy rains sustained moisture surpluses along the Gulf of Guinea coast between Cote d’Ivoire and Benin. During the past 30 days, rainfall remained largely below-average over Zimbabwe and central Mozambique, with deficits exceeding 100 mm in local areas. Rainfall was also below average over parts of Madagascar, northeastern South Africa, southern Malawi, much of Zambia, northern Angola, and eastern Botswana. Rainfall was significantly above average over southwestern Angola and northwestern Namibia. Above average rainfall was also seen in in much of Tanzania. Below average moisture conditions were present over eastern Kenya, while the west, Uganda , parts of central Africa, and the Gulf of Guinea region received moisture surpluses. During the past 90 days, rainfall was above average over southern Angola, northern Namibia, the areas along the border between Tanzania and Mozambique, and much of Madagascar. However, rainfall was below average over the remainder areas of continental southeastern Africa. Eastern Kenya, southern Somalia received below average rainfall. Rainfall was also below average over southern DRC, central Congo, Gabon. Rainfall was above average over northern DRC, parts of CAR, southern Cameroon, and the area along the Gulf of Guinea coast. Week-1 outlooks call for an increased chance for above average rainfall along the Gulf of Guinea coast and coastal central Africa. There is also an increased chance for above average rainfall over parts of Ethiopia, southern Sudan, northern Uganda and northern Kenya.