The African Monsoon Recent Evolution and Current Status

1. The African Monsoon Recent Evolution and Current Status Update prepared by Climate Prediction Center / NCEP 31 August 2009 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 soaked parts of Senegal and resulted in flooding in many local areas. Southwestern Ethiopia also registered sizable rainfall amounts. • The area encompassing Chad and Sudan continued to register moisture deficits.

4. Rainfall Patterns: Last 7 Days During the past seven days heavy rains pounded the western sector of Senegal resulting in flooding at many localities. However, rainfall was near average in the remainder part of the Sahel. Rainfall was below average over local areas in the Gulf of Guinea region and parts of central Africa. Rainfall was above average over local areas in southwestern and northwestern Ethiopia as well as parts of Eritrea.

5. Rainfall Patterns: Last 30 Days During the past 30 days rainfall was above average over the western end of the Sahel and in most areas over the Guineas and Sierra Leone. Rainfall was near average in most areas in the Sahel, except for local areas in southern Niger. Light rains sustained moisture deficits in Chad along the boundary with Sudan as well as most areas in central and southern Sudan, and local areas in northern Ethiopia. Rainfall was above average over parts of central Africa, including northern DRC, and southwestern Cameroon.

6. Rainfall Patterns: Last 90 Days During the past 90 days rainfall was above average over the western part of the Sahel, and near average in areas from western Mali to western Niger. Rainfall was below average in portions of southern Niger, Chad, Sudan, parts of western Ethiopia, as well as the areas in the Gulf of Guinea region. In central Africa, rainfall was above average over Cameroon, western CAR, and northwestern DRC.

7. Rainfall Patterns: Last 180 Days During the past 180 days rainfall was above average over western Senegal and below average in parts of the Gulf of Guinea region. Rainfall was significantly below average over Sudan Ethiopia, Kenya, and Uganda.

8. Recent Rainfall Evolution Daily evolution of precipitation during the last 90 days shows that season-to-date totals are above average over western sector of the Sahel (lower panel – left). Light rains over the past several weeks sustained moisture deficits along the border of Chad and Sudan (lower panel – right). Rainfall continued to be below average over southwestern Ethiopia (upper panel – right).

9. Atmospheric Circulation:Last 7 Days The 850 hPa wind anomaly (left panel) reflected westerly wind anomalies from the tropical central Atlantic into West Africa. An anomalous cyclonic system is evident over northwestern Africa. The 200 hPa wind anomaly featured an anomalous anticyclonic circulation over northwestern Africa and a cyclonic/anticyclonic couplet in the southern hemisphere.

10. NCEP GEFS Model ForecastsNon-Bias Corrected Probability of precipitation exceedance Week-1: Valid 1 - 7 September, 2009Week-2: Valid 8 – 14 September, 2009 For week-1 and week-2, the global ensemble forecast system (GEFS) suggests over a 90% chance for precipitation to exceed 25 mm over the southern areas of western Sahel, the northern areas of the Gulf of Guinea region, and parts of central Africa.

11. Experimental Week-1 Precipitation Outlooks Week-1 Outlook 1-7 September, 2009 An increased chance for above average rainfall over the western parts of the Sahel and the Gulf of Guinea region: The strong meridional SST gradient between the Gulf of Guinea and the tropical eastern Atlantic and the GFS projected low level westerly wind anomalies are expected to enhance precipitation in the region. Confidence: Moderate

12. Experimental Week-2 Precipitation Outlooks Week-2 Outlook 8-14 September, 2009 No Forecasts.

13. Summary • During the past seven days heavy rains pounded the western sector of Senegal resulting in flooding at many localities. However, rainfall was near average in the remainder part of the Sahel. Rainfall was below average over local areas in the Gulf of Guinea region and parts of central Africa. Rainfall was above average over local areas in southwestern and northwestern Ethiopia as well as parts of Eritrea. • During the past 30 days rainfall was above average over the western end of the Sahel and in most areas over the Guineas and Sierra Leone. Rainfall was near average in most areas in the Sahel, except for local areas in southern Niger. Light rains sustained moisture deficits in Chad along the boundary with Sudan as well as most areas in central and southern Sudan, and local areas in northern Ethiopia. Rainfall was above average over parts of central Africa, including northern DRC, and southwestern Cameroon. • For week-1, there is an increased chance for above average rainfall over the western parts of the Sahel and the Gulf of Guinea region. It is a no forecast for week-2.