The South American Monsoon System Summary July 2009-June 2010

1. The South American Monsoon System SummaryJuly 2009-June 2010 Update prepared by Climate Prediction Center / NCEP June 2010 For more information, visit:http://www.cpc.ncep.noaa.gov/products/Global_Monsoons/American_Monsoons

2. Summary • The rainy season onset phase (SON) was delayed over the Amazon basin. This resulted in large rainfall deficits (greater than 100 mm) throughout the basin during September-November 2009. • During the mature phase of the monsoon (DJF) rainfall was below average over central and southeastern Brazil, and above average over Southeast South America, which are features consistent with El-Nino conditions in the tropical Pacific. • During the decay phase of the rainy season (MAM), below-average rainfall was observed over northeastern Brazil, southern Amazon basin and portions of central Brazil (monsoon core region), consistent with El Niño conditions in the tropical Pacific. • In general, the pattern of rainfall departures for the water year (July 2009-June 2010) is similar to the composite for El Niño episodes.

3. Outline • Onset phase • Mature phase • Decay phase • Long-Term Departures from Average • Summary

4. Precipitation Climatology ONSET DATES

5. Precipitation Departures: Onset Phase (Sep-Nov 2009) During September-November 2009 rainfall was below average over most of northwestern South America, with rainfall deficits exceeding 200 mm throughout the Amazon basin and exceeding 400 mm over portions of Colombia and Venezuela. Much above-average rainfall was observed over Southeast South America (southern Brazil, Uruguay, southern Paraguay and portions of northeastern Argentina).

6. Tropical Pacific and Atlantic SST Anomalies (Sep-Nov 2009) During September–November 2009, equatorial SSTs were above average over most of the Pacific Ocean and near average along the west coast of South America (Ecuador). In the Atlantic, equatorial SSTs were near average from northeastern South America to the West African coast. Positive SST anomalies dominated the subtropical North and South Atlantic Oceans.

7. Precipitation Departures: Mature Phase (Dec 2009-Feb 2010) During December 2009-February 2010 rainfall was below average over most of Brazil north of 20S (red oval), with rainfall deficits greater than 200 mm in many areas. Much-above-average rainfall was observed over portions of the southern Amazon basin and Southeast South America (Paraguay, northeastern Argentina, Uruguay and southern Brazil)

8. Tropical Pacific and Atlantic SST Anomalies (Dec09-Feb10) During December 2009–February 2010, equatorial SSTs were much above average over the Pacific from 180W to 90W, with largest positive anomalies evident in the central Pacific. This pattern is consistent with El Niño conditions. Over the Atlantic equatorial SSTs were slightly above average from northern South America to the African coast. Positive SST anomalies dominated the subtropical Atlantic north and south of the equator.

9. Precipitation Climatology END DATES

10. Precipitation Departures: Decay Phase (Mar-May 2010) During March-May 2010 rainfall was below average throughout most of South America. Deficits greater than 200 mm were observed in the southern Amazon basin. Above-average rainfall was observed over central Colombia, portions of eastern Brazil and portions of southern Brazil.

11. Tropical Pacific and Atlantic SST Anomalies (Mar-May 2010) During March-May 2010, equatorial SSTs were above average in the Pacific Ocean, but departures were less than the previous season, as El Niño conditions weakened. Over the Atlantic, SSTs were above average throughout the Tropics and Subtropics.

12. Madden-Julian Oscillation Review (Dec 2009 – May 2010) Positive anomalies (brown shading) indicate unfavorable conditions for precipitation Negative anomalies (green shading) indicate favorable conditions for precipitation 200-hPa Velocity Potential Anomalies (5°S-5°N) Eastward propagation associated with the MJO was evident during early-mid January (red box). During February and the first half of March, the MJO weakened and anomalies became more stationary and incoherent on the intraseasonal time scale (black boxes). In mid-March, weak upper-level divergence (convergence) developed over Africa and the Indian Ocean (Maritime continent) and these anomalies propagated eastward. In late April and early May, anomalies increased and eastward propagation was evident and was associated with the MJO. Most recently in late May and early June, upper-level divergence is evident from 80W to 30E. Time Longitude

13. Precipitation Departures: July 2009-June 2010 During 1 July 2009-6 June 2010 rainfall was below average throughout most of northern South America (north of 20S), while much above-average rainfall was observed over Southeast South America.

14. Precipitation Anomaly Patterns during El Niño Episodes over Brazil 2009-2010 The pattern of anomalous precipitation over Brazil for the water year (July 2009-June 2010, figure above) is consistent with the El-Nino composite.Wetter than average to the south and drier than average to the north. From Silva et al., 2007

15. Summary • The rainy season onset phase (SON) was delayed over the Amazon basin. This resulted in large rainfall deficits (greater than 100 mm) throughout the basin during September-November 2009. • During the mature phase of the monsoon (DJF) rainfall was below average over central and southeastern Brazil, and above average over Southeast South America, which are features consistent with El-Nino conditions in the tropical Pacific. • During the decay phase of the rainy season (MAM), below-average rainfall was observed over northeastern Brazil, southern Amazon basin and portions of central Brazil (monsoon core region), consistent with El Niño conditions in the tropical Pacific. • In general, the pattern of rainfall departures for the water year (July 2009-June 2010) is similar to the composite for El Niño episodes.