The African Monsoon Recent Evolution and Current Status

1. The African Monsoon Recent Evolution and Current Status Update prepared by Climate Prediction Center / NCEP 12 May 2008 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 • Experimental Week-1 Outlook • Summary

3. Highlights:Last 7 Days • Light rains continued to sustain moisture deficits over most seasonal crop areas in Africa, including the Greater Horn of Africa, and the Gulf of Guinea region.

4. Rainfall Patterns: Last 180 Days Over the past 180 days, rainfall was below average over central Ethiopia, western Kenya, Uganda, and northeastern DRC. Rainfall was also below average over parts of the Gulf of Guinea region. Rainfall was above average over portions of Tanzania and in many areas in southern Africa, except for northern and eastern Madagascar, and local areas in southern Zimbabwe and Mozambique.

5. Rainfall Patterns: Last 90 Days Over the past 90 days, rainfall was below average over central Ethiopia southward into northern Kenya and Uganda, extending west to the Gulf of Guinea region. Rainfall was also below average over most areas in central Africa and the northern sector of southern Africa. Rainfall was above average over northeastern Mozambique, along the coast of Tanzania, and over central Namibia.

6. Rainfall Patterns: Last 30 Days Over the last 30 days, rainfall was below average over western Kenya, Uganda, northwestern Tanzania, and north central Ethiopia. Rainfall was also below average over portions of central Africa and the Gulf of Guinea region. In the south, rainfall was below average along the east coast of Madagascar and central Mozambique. Rainfall was slightly above average in local areas in southern Africa.

7. Rainfall Patterns: Last 7 Days During the past 7 days, rainfall was below average over southern Ethiopia, northern and central Kenya, portions of Uganda. Rainfall was also below average over parts of DRC and in most areas in the Gulf of Guinea region, except for local areas in northern Cameroon and southwestern Cote d’Ivoire, which received slightly above average rainfall.

8. Recent Rainfall Evolution Moisture deficits persisted in portions of the northern Horn of Africa (top panel - right); Despite a few showers over the past few days, western Kenya and Uganda continued to register a cumulative rainfall shortage (bottom panel – right); Below average rains continued to sustain moisture deficits over parts of the Gulf of Guinea region (bottom panel – left).

9. Atmospheric Circulation:Last 7 Days Over the past 7 days, the 850 hPa wind anomaly (left panel) featured a weakening of both the southern hemisphere and northern hemisphere subtropical ridges. This low level circulation is associated with an anomalous upper level cyclonic circulation across northwestern Africa (right panel). These features will tend to inhibit rainfall over West Africa.

10. Rainfall Climatology: 13-19 May Rainfall totals for the week 13-19 May range between 15 and 45 mm over the Gulf of Guinea region, parts of the GHA and central Africa. Rainfall totals range between 45 and 75 mm over parts of central Africa.

11. NCEP GEFS Model ForecastsNon-Bias Corrected Probability of precipitation exceedance – Week-1Valid 13-19 May, 2008 NCEP global ensemble forecast system (GEFS) suggests a high tilt in the odds (90% or above) for precipitation to exceed 25 mm along coastal Kenya and Tanzania, the western Ethiopian highlands, central Africa, and over the Gulf of Guinea region (left panel). Areas with highest chance for precipitation to exceed 50 mm (right panel) include the coastal boundary between Kenya and Tanzania, local areas in Ethiopia, Gabon, and sections along coastal Gulf of Guinea.

12. Experimental Week-1 Precipitation OutlookValid 13-19 May, 2008 • An increased chance for below average • rainfall along the Guinean coastline: • The suppressed phase of the weak MJO and the lack • Of moisture advection from the Gulf of Guinea • Will result in below average rainfall in this region. • Confidence: High

13. Summary • Over the past 7 days, light rains sustained moisture deficits over many areas in the Greater Horn of Africa, including Ethiopia, parts of Kenya and Uganda. Rainfall eased along the coast of Tanzania, which received moderate to heavy rains over the past several weeks. Rainfall was also below average over parts of eastern and central DRC, extending west to Congo, eastern Gabon, and southern Cameroon. Rainfall was slightly below average over most areas in the Gulf of Guinea region, except for a few localities in southwestern Cote d’Ivoire, central Nigeria, and northern Cameroon, where rainfall was slightly heavier than average. • The rainfall suppression of the past week resulted in an increase in cumulative moisture deficits over the past 30 days in all the major seasonal crop areas of Africa, including the Greater Horn of Africa and the Gulf of Guinea region. However, despite this rainfall shortage, many areas in these regions have been receiving rainfall, especially the area encompassing southwestern Kenya and Uganda. Areas of concern include northern Ethiopia, where little or no rain has been registered for several weeks and where cumulative rainfall totals are only one third of average over the past 90 days. Areas in the Gulf of Guinea region also registered only less than one half of the cumulative average rainfall over the past 90 days. • For the period 13–19 May 2008, there is an increase chance for below average rainfall along the Guinean coastline.