The African Monsoon Recent Evolution and Current Status Update prepared by Climate Prediction Center / NCEP 07 July 2008 For more information, visit:

Outline Highlights Recent Evolution and Current Conditions NCEP GEFS Forecasts Experimental Week-1 Outlook Summary

Highlights: Last 7 Days Moderate to heavy rains sustained moisture surpluses over parts of the Sahel, including portions of Burkina Faso and southern Mali. Above average rains persisted over eastern Guinea and parts of the Gulf of Guinea region. However, parts of eastern Nigeria had below normal rainfall. Light rains sustained moisture deficits over southwestern Ethiopia. Development of first tropical storm of the season over Atlantic resulting from the synoptic wave activity over west Africa.

Rainfall Patterns: Last 180 Days Over the past 180 days, rainfall was below average over most areas in the Gulf of Guinea region, central Africa, and many areas in East Africa. Rainfall was above average in portions of northwestern southern Africa, and local areas in northern Mozambique and Tanzania.

Rainfall Patterns: Last 90 Days Over the past 90 days, rainfall was overall below average over most areas in Africa.

Rainfall Patterns: Last 30 Days Over the last 30 days, rainfall was below average over parts of the Gulf of Guinea region, and areas in East Africa, including portions of Sudan and western Ethiopia.

Rainfall Patterns: Last 7 Days During the past 7 days, rainfall was above average over parts of the Sahel and portions of the Gulf of Guinea region. However, parts of eastern Nigeria and pockets along the Gulf of Guinea coast received below average rainfall. Rainfall was also below average over part of Sudan and western Ethiopia. Other developments include the development of first tropical storm of the season Bertha in the Atlantic due to the wave activity over west Africa.

Recent Rainfall Evolution The moderate to heavy rains of the past week helped bring cumulative rainfall over the last 30 days closer to climatology in many areas in the Sahel (bottom panel – left). Rainfall remained below average over part of the Gulf of Guinea, parts of eastern Nigeria and parts of northwestern Ethiopia (Right panels).

SST: Last 7 Days 29 June - 05 July 2008 The mean SST map (left panel) features a strengthening of the Atlantic cold tongue, which developed in early June. SST off the coast of tropical west Africa north of the equator have weakened but remains warmer than average. Below normal SST prevailed along the east coast of Africa. MeanAnomalies

Atmospheric Circulation: Last 7 Days Over the past 7 days, the 850 hPa wind anomaly (left panel) featured a strengthening of the westerly wind anomalies in the eastern Atlantic just north of the equator. Easterly wind anomalies in the central IO were evident over the equatorial central IO. The 200 hPa wind anomaly (right panel) featured westerly wind anomalies extending from equatorial eastern Africa into the IO. Easterly wind anomalies were evident from Asia to northern Africa.

NCEP GEFS Model Forecasts Non-Bias Corrected Probability of precipitation exceedance Week-1: Valid 8 – 14 July, 2008 Week-2: Valid July, 2008 NCEP global ensemble forecast system (GEFS) suggests for week-1 and week-2 a high tilt in the odds (90% or above) for precipitation to exceed 50 mm over parts of the Gulf of Guinea region, CAR and western Ethiopia.

Experimental Week-1 Precipitation Outlook Valid July, An increased chance for above average rainfall over the Gulf of Guinea region and the Sahel An enhanced West African monsoon system associated with favorable winds, warmer SST anomalies over the Gulf of Guinea region and active phase of MJO will likely result in enhanced rainfall over the west African region. Confidence: High 2.An increased chance for above-average rainfall over western Ethiopia. A general low pressure and moisture advection from the western Indian Ocean are expected to enhance precipitation. Confidence: Moderate

Experimental Week-2 Precipitation Outlook Valid July, An increased chance for above average rainfall over the Gulf of Guinea region, Sahel and Central Africa. An enhanced West African monsoon system associated with the active phase of MJO and favorable winds is expected to Increase precipitation over the region. Confidence: Moderate

Summary Over the past 7 days, beneficial rains continued to fall across the Sahel from Niger to Senegal, resulting in above average rainfall in many areas in Burkina Faso and western Mali. Rainfall was near-normal over parts of the Gulf of Guinea region, including portions of Cote d’Ivoire, northern Ghana, and the southern areas of Togo and Benin. There were dry pockets in Sierra Leone and Liberia, and in southern Ghana. Light rains resulted in moisture deficits in the previously wet area of southwestern Ethiopia. Seasonably dry weather prevailed in most areas in central and southern Africa. The recent increase in rainfall over West Africa resulted in cumulative above average rainfall over the last 30 to 90 days in parts of the Sahel portions of Burkina Faso and Mali. many areas in West Africa over the past 30 and 90 days remain below average. Overall, Burkina Faso and southern Mali rainfall over the last 30 days has caught up with the climatological cumulative 30-day rainfall totals. However, cumulative rainfall deficits over the last 90-days are in the range between 30 and 150 mm over the central and southern areas of Burkina Faso. Rainfall was slightly above average over western Mali over the last 90 days. For the period 8-14 July 2008 through week-2 (15-21 July, 2008), there is an increased chance for above average rainfall over the Gulf of Guinea region parts of the Sahel and western Ethiopia.