The African Monsoon Recent Evolution and Current Status Update prepared by Climate Prediction Center / NCEP 6 July 2010 For more information, visit:

Outline Highlights Recent Evolution and Current Conditions NCEP GEFS Forecasts Summary

Highlights: Last 7 Days During the past seven days, heavy rains may have resulted in flooding in local areas in southwestern Mali, while the west coast of Senegal registered its first significant rainfall amount this season. Rainfall diminished significantly over Burkina Faso during the period.

Rainfall Patterns: Last 7 Days During the past seven days, in the Sahel, for the first time this season, the western areas of Senegal registered significant rainfall amounts, and the east increased its moisture surpluses. Heavy rains pounded local areas in southwestern Mali, while lighter rains fell over Burkina Faso and western Niger. Rainfall also diminished over most areas in the Gulf of Guinea region and in central Africa, except for southern Cameroon, where totals were above average. Rainfall was also locally moderate to heavy in southern Sudan, western Ethiopia, southwestern Kenya, and northeastern Uganda.

Rainfall Patterns: Last 30 Days During the past 30 days, rainfall was above average in the southern half of Senegal, southwestern Mali, and portions of Niger. Rainfall was also above average along portions of the Gulf of Guinea from Cote d’Ivoire to Nigeria. The western part of central Africa received above average rainfall. Further to the east, rainfall was suppressed over southern Sudan and enhanced in western Ethiopia.

Rainfall Patterns: Last 90 Days During the past 90 days, southeastern Guinea, Liberia, and coastal areas of Cote d’Ivoire experienced above average rainfall. However, rainfall was below average over parts of northern Nigeria. Rainfall was above average over the western end of central Africa, but moisture deficits prevailed over southern DRC. Rainfall was locally heavy in portions of the of the Greater Horn of Africa, but suppressed in central Kenya and much of Tanzania.

Rainfall Patterns: Last 180 Days During the past 180 days, rainfall was above average along the western Gulf of Guinea coastline, much of central and eastern Africa, and parts of southern Africa. However, Tanzania and western, central and the northern tip of Madagascar had below average rainfall.

Recent Rainfall Evolution Daily evolution of precipitation during the last 90 days at selected regions indicates a good start to the rainy season in western Senegal (lower panel – left). Despite the dry spell of the previous week, cumulative totals remain above average in central Burkina Faso (bottom panel – right). Moisture surpluses continue to increase in western Ethiopia (upper panel – right).

Atmospheric Circulation: Last 7 Days The 850 hPa wind anomaly (left panel) reflected westerly wind anomalies across the tropical eastern Atlantic converging with low level easterly wind anomalies over the western part of the Sahel, resulting in enhanced rainfall in this region. The 200 hPa wind anomaly (right panel) featured an upper level anticyclonic- cyclonic-anticyclonic triplet extending from the eastern Atlantic to Asia. This system is associated with a strengthening of a subtropical ridge in the southern hemisphere and consistent with enhanced rainfall in western Africa.

NCEP GEFS Model Forecasts Non-Bias Corrected Probability of precipitation exceedance Week-1: Valid June, 2010 Week-2: Valid 14 – 20 July, 2010 For week-1, there is a high chance for precipitation to exceed 50 mm over parts of Guinea, Sierra Leone, along the coast of Nigeria and parts of Cameroon. There is also a high chance for rainfall to exceed 50 mm over western Ethiopia. For week-2, there is a high chance for precipitation to exceed 50 mm over Guinea and parts of western Ethiopia.

1. There is an increased chance for above average rainfall over western Sahel: Low level westerly wind anomalies from the Atlantic associated with an anomalous cyclonic circulation are expected to enhance rainfall in the region. Confidence: Moderate 2. There is an increased chance for below average rainfall along the Gulf of Guinea coast. The anomalous low level divergence and the northward shift of moisture convergence away from the Gulf of Guinea are expected to suppress rainfall in this region. Confidence: Moderate 3. There is an increased chance for above average rainfall over western Ethiopia: The stronger than normal moist cross equatorial flow from the southern hemisphere is expected to enhance rainfall in the region. Confidence: Moderate Experimental Week-1 Precipitation Outlooks Week-1 Outlook 7 July – 12 July, 2010

Experimental Week-2 Precipitation Outlooks Week-2 Outlook 13 – 19 July, 2010 No forecast – Climatology suggested.

Summary During the past seven days, in the Sahel, for the first time this season, the western areas of Senegal registered significant rainfall amounts, and the east increased its moisture surpluses. Heavy rains pounded local areas in southwestern Mali, while lighter rains fell over Burkina Faso and western Niger. Rainfall also diminished over most areas in the Gulf of Guinea region and in central Africa, except for southern Cameroon, where totals were above average. Rainfall was also locally moderate to heavy in southern Sudan, western Ethiopia, southwestern Kenya, and northeastern Uganda. During the past 30 days, rainfall was above average in the southern half of Senegal, southwestern Mali, and portions of Niger. Rainfall was also above average along portions of the Gulf of Guinea from Cote d’Ivoire to Nigeria. The western part of central Africa received above average rainfall. Further to the east, rainfall was suppressed over southern Sudan and enhanced in western Ethiopia. During the past 90 days, southeastern Guinea, Liberia, and coastal areas of Cote d’Ivoire experienced above average rainfall. However, rainfall was below average over parts of northern Nigeria. Rainfall was above average over the western end of central Africa, but moisture deficits prevailed over southern DRC. Rainfall was locally heavy in portions of the of the Greater Horn of Africa, but suppressed in central Kenya and much of Tanzania. For week-1, there is an increased chance for above average rainfall over the western areas of the Sahel and Ethiopia. There is an increased chance for below average rainfall along the Gulf of Guinea coast.