The African Monsoon Recent Evolution and Current Status Update prepared by Climate Prediction Center / NCEP 29 June 2009 For more information, visit:

Outline Highlights Recent Evolution and Current Conditions NCEP GEFS Forecasts Summary

Highlights: Last 7 Days Moderate to heavy rains were received across the Gulf of Guinea and in parts of the western Sahel region. A belt of below average precipitation extends from parts of Niger and Nigeria eastward to Sudan.

Rainfall Patterns: Last 7 Days In the last seven days, favorable amounts of precipitation were observed throughout the Gulf of Guinea countries, with locally heavy accumulations seen in parts of Burkina Faso, and western Mali and Senegal. A pocket of below-average precipitation was received in northern Burkina Faso, and in western Niger, with the greatest decrease in 7-day rains seen throughout central and northern Nigeria, and across central Chad and Sudan. In eastern Africa, dry conditions persisted in southwestern Sudan and northern Uganda, while the eastern rim of the Ethiopia’s Rift Valley was anomalously wet.

Rainfall Patterns: Last 30 Days During the last 30 days, rainfall continued to remain above average in the lower Gulf of Guinea region. Precipitation totals have been considerably below average throughout central and northern Nigeria, as this dryness has extended eastward across the Sahel to Sudan. The greatest rainfall deficits remain concentrated in southeastern Sudan and northern Uganda. Western Ethiopia has sustained above-average rainfall totals, with moderate dryness in local parts of southern Ethiopia over the last month.

Rainfall Patterns: Last 90 Days Since the end of March, pockets of below-average have affected parts of Burkina Faso, Cote d’Ivoire, Ghana and central Nigeria. The greatest rainfall deficits have been observed across the Greater Horn, impacting much of Kenya, Uganda, and in areas along the Rift Valley of Ethiopia. In southern Africa, rains have been anomalously dry across much of Angola, Zambia, Zimbabwe, Mozambique, and Madagascar. Further South, anomalously wet conditions remain over many local areas in of South Africa over the last 90 days.

Rainfall Patterns: Last 180 Days Over the past 180 days, significantly wet conditions were seen along the Angola and Namibia border, with prevalent dryness seen in northern Angola and extending into parts of DRC. Below-average conditions were also observed along the northwest coast of Madagascar, as well as across a number of regions in Kenya, Uganda, and Ethiopia.

Recent Rainfall Evolution Daily evolution of precipitation during the last 30 days shows that the recent increase in rainfall activity has eliminated seasonal deficits across parts of the Gulf of Guinea region (bottom left). Along the Kenya/Tanzania border, a slightly premature end of seasonal rains has sustained precipitation deficits near Lake Victoria (bottom right). In northeastern Nigeria, inadequate moisture has resulted in a gradual strengthening rainfall anomalies since early June.

Atmospheric Circulation: Last 7 Days 850 hPa wind anomaly analysis (left panel) reflects anomalous easterly winds over the Gulf of Aden, and cyclonic flow over western Sahel and Gulf of Guinea, suggesting ample moisture availability for heavy rainfall in the last 7 days. The 200 hPa wind anomaly (right panel) shows subtropical trough axis extended over the Sahara with anomalously strong westerlies over the central Sahel.

NCEP GEFS Model Forecasts Non-Bias Corrected Probability of precipitation exceedance Week-1: Valid 30 June - 6 July, 2009 Week-2: Valid 7 – 13 July, 2009 For week-1 the global ensemble forecast system (GEFS) suggests over a 90% chance for precipitation to exceed 50 mm along coastal Guinea, and into portions of Nigeria/Cameroon. For week-2 chances for precipitation to exceed 50 mm is placed more towards the north, suggesting relief for anomalously dry regions of the Sahel. Western Ethiopia is likely to receive favorable rains for the next 2 weeks.

Experimental Week-1 Precipitation Outlooks Week-1 Outlook 30 June - 6 July, An increased chance for above average rainfall over parts of the Gulf of Guinea countries: The projected MJO signal and the convergence of anomalous southerlies from warm equatorial Atlantic Ocean are expected to enhance precipitation in the region. Confidence: Moderate

Experimental Week-2 Precipitation Outlooks Week-2 Outlook July, 2009 An increased chance for above average Rainfall over the Gulf of Guinea countries: The projected MJO signal is expected to enhance precipitation in the region. Confidence: Moderate

Summary During the past week, moderate to heavy precipitation was observed throughout and Gulf of Guinea and across the western Sahel. Pockets of below-average rainfall were received in parts of Burkina Faso and Niger, with strengthening deficits seen in central and northeastern portions of Nigeria. Although moderate rains were observed in southern Sudan, precipitation has remains well below average. During the last 30 days, rainfall was above average over the lower Gulf of Guinea region. Rainfall continues to remain below average over most areas from Nigeria eastward to Sudan and southwestern Ethiopia. For week-1 outlook (valid 30 June – 6 July 2009), there is an increased chance for above average rainfall over parts of the Gulf of Guinea countries.