1. The South American Monsoon System: Recent Evolution and Current Status Update prepared by Climate Prediction Center / NCEP 20 December 2010 For more information, visit: http://www.cpc.ncep.noaa.gov/products/Global_Monsoons/American_Monsoons http://www.cpc.ncep.noaa.gov/products/Global_Monsoons/American_Monsoons

2. Outline Highlights Recent Evolution and Current Conditions NCEP/GFS Model Forecasts Climatology

3. Highlights During the last 7 days, below-average rainfall was observed over northern Peru, part of western Brazil, and south of 10S (except southern Brazil). Above-average rainfall was observed over Colombia, Ecuador, and much of northern Brazil. For the week of 20-26 December, the NCEP GFS predicts above- average rainfall over Colombia, southern Peru, southern Bolivia, Paraguay, and southern Brazil, and below-average rainfall over a large part of Brazil (especially its eastern portion), northeastern Argentina, southeastern Venezuela, and Nicaragua.

4. Rainfall Total & Anomaly Patterns: Last 7 Days During the last 7 days, below-average rainfall was observed over northern Peru, part of western Brazil, and south of 10S (except southern Brazil). Above-average rainfall was observed over Colombia, Ecuador, and much of northern Brazil. TotalAnomaly

5. Rainfall Totals & Anomaly Patterns: Last 30 Days During the last 30 days, below-average rainfall was observed over much of South America especially western Brazil, Bolivia, northern Argentina, and Uruguay. Above-average rainfall was observed over Costa Rica, Panama, Colombia, and eastern and southern Brazil. The long-term dry pattern over southeastern South America (Paraguay, Uruguay, and northeastern Argentina) is consistent with the ongoing La Nina conditions. TotalAnomaly

6. BP Recent Evolution: Rainfall Last 90 Days BP: Brazilian Plateau 90-day accumulated rainfall remains below average over the southern Amazon Basin. Also, slightly below-average rainfall continues over the core monsoon region (BP), where deficits have been steadily decreasing in recent weeks. 90-day accumulated rainfall in southern Brazil has turned from below average to above average, after a rainfall deficit for about two months.

7. Tropical Pacific and Atlantic SST Anomalies During the last week, equatorial SSTs were between 0.5° - 2.0°C below average over most of the central and eastern Pacific Ocean. SSTs were 0.5°-1.5°C above average in most of the tropical Atlantic. A La-Nina event is in progress in the tropical Pacific (for more details go to the link below). A weekly PowerPoint summarizing the ENSO Cycle: Recent Evolution, Current Status and Predictions is available at: http://www.cpc.noaa.gov/products/precip/CWlink/MJO/enso.shtml

8. Atmospheric Circulation Recent 7 days Rising motion (negative omega, yellow/red shading), usually associated with wetter- than- normal conditions. Sinking motion (positive omega, blue shading), usually associated with drier-than-normal conditions. Upper panels: During 12-18 Dec 2010, anomalous anticyclonic circulation dominated southern South America and the Atlantic, while divergent anomalous zonal flow dominated Brazil. Lower panels: Anomalous rising motion was observed over Colombia, northern Brazil, and southeastern Brazil where above-average rainfall occurred (see slide 4). Anomalous sinking motion appeared over northern Argentina where below-average rainfall was observed.

9. 925-hPa Wind &Temperature Recent 30 DaysRecent 7 Days Low-level (~600 m) wind and temperature anomalies based on the NCEP Climate Data Assimilation Systems (CDAS) analysis. The patterns of anomalous temperature and wind at 925-hPa are usually similar to surface observations. Note: Areas with surface pressure below 925-hPa are masked out. During the 7-day period of 12-18 Dec 2010, below-average temperature was observed over southern South America.

10. NCEP/GFS Model Forecasts Bias-Corrected Precipitation Total Forecasts from 20 December 2010 – Days 1-7 Anomaly Note: Note: Bias correction based on last 30-day forecast error.

11. NCEP/GFS Model Forecasts Bias-Corrected Precipitation Total Forecasts from 20 December 2010 – Days 8-14 Anomaly Note: Note: Bias correction based on last 30-day forecast error.

12. For Days 1-7 (20-26 Dec), above-average rainfall is predicted over Colombia, southern Peru, southern Bolivia, Paraguay, and southern Brazil, while below-average rainfall is predicted over a large part of Brazil (especially its eastern portion), northeastern Argentina, southeastern Venezuela, and Nicaragua. For Days 8-14 (27 Dec – 2 Jan), above-average rainfall is predicted over eastern Brazil and Colombia, while below-average rainfall is predicted over equatorial and northern tropical South America (except Colombia), southwestern Brazil, and northern Argentina. NCEP/GFS MODEL FORECASTS NOTE: See forecast verification in the next slide.

13. Forecast Verification Forecast from 6 Dec 2010 Valid 13-19 Dec 2010 Forecast from 13 Dec 2010 Valid 13-19 Dec 2010 Observed 13-19 Dec 2010

14. Climatology Rainy Season Dates ONSETDEMISE

15. Precipitation Climatology

16. Precipitation Climatology Animation