The South American Monsoon System: Recent Evolution and Current Status

1. The South American Monsoon System: Recent Evolution and Current Status Update prepared by Climate Prediction Center / NCEP 28 March 2011 For more information, visit: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, above-average rainfall was observed over northwestern South America, central Brazil, Uruguay and its adjacent regions in Brazil and Argentina. Below-average rainfall was observed over eastern and southwestern Brazil, eastern Bolivia, Paraguay, northeastern Argentina, and portions of southern Brazil. • For 28 March – 3 April, above-average rainfall is predicted for western South America (west of 70ºW), central and southern Brazil, northern and southern Bolivia, and Paraguay, while below-average rainfall is predicted for northeastern South America, eastern Brazil, northeastern Argentina, Uruguay, and extreme southern Brazil. For 4-10 April, above-average rainfall is predicted for most of South America north of 22ºS except Venezuela, eastern Brazil, and Bolivia where below-averaged rainfall is forecasted. Below-average rainfall is also predicted over northeastern Argentina, Uruguay, and extreme southern Brazil for week 2.

4. Rainfall Total & Anomaly Patterns:Last 7 Days Total Anomaly During the last 7 days, above-average rainfall was observed over northwestern South America, central Brazil, Uruguay and its adjacent regions in Brazil and Argentina. Below-average rainfall was observed over eastern and southwestern Brazil, eastern Bolivia, Paraguay, northeastern Argentina, and portions of southern Brazil.

5. Rainfall Totals & Anomaly Patterns:Last 30 Days Total Anomaly During the last 30 days, above-average rainfall was observed over most of the areas east of 60ºW and north of 22ºS. Above-average rainfall was also observed over Colombia and portions of northern and southern Peru. Below-average rainfall was seen over western Brazil, central and northeastern Peru, Bolivia, northeastern Argentina, Uruguay, and extreme southern Brazil.

6. BP Recent Evolution: RainfallLast 90 Days BP: Brazilian Plateau • 90-day rainfalls are slightly above average over the southern Amazon Basin. Above-average rainfall was also observed over the core monsoon region (BP). • 90-day totals are below average in southern Brazil due to the deficient rainfall in March.

7. Tropical Pacific and Atlantic SST Anomalies During the last week, equatorial SSTs were 0.5° - 1.5°C below average over most of the central Pacific Ocean. SSTs were about 1.0°C above average in the equatorial Atlantic. A La-Nina event is still 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 • Upper panels: During 19-25 Mar 2011, anomalous easterly flow was observed in the upper troposphere over northern South America (north of 15ºS). • Lower panels: Anomalous rising motion (negative omega) was observed over northwestern South America where rainfall was mostly above average (see Slide 4), and anomalous sinking motion was seen over eastern Brazil where rainfall was below average. 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.

9. 925-hPa Wind &Temperature Recent 30 Days Recent 7 Days • During the last 7-day period (19-25 Mar 2011), near-average temperatures were observed over South America. 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.

10. NCEP/GFS Model Forecasts Bias-Corrected Precipitation Forecasts from 28 March 2011 – Days 1-7 Total Anomaly Note: Bias correction based on last 30-day forecast error.

11. NCEP/GFS Model Forecasts Bias-Corrected Precipitation Forecasts from 28 March 2011– Days 8-14 Total Anomaly Note: Bias correction based on last 30-day forecast error.

12. NCEP/GFS MODEL FORECASTS • For Days 1-7 (28 Mar – 3 Apr), above-average rainfall is predicted for western South America (west of 70ºW), central and southern Brazil, northern and southern Bolivia, and Paraguay, while below-average rainfall is predicted for northeastern South America, eastern Brazil, northeastern Argentina, Uruguay, and extreme southern Brazil. • For Days 8-14 (4-10 Apr), above-average rainfall is predicted for most of South America north of 22ºS except Venezuela, eastern Brazil, and Bolivia where below-averaged rainfall is forecasted. Below-average rainfall is also predicted over northeastern Argentina, Uruguay, and extreme southern Brazil.

13. Forecast Verification Forecast from 14 Mar 2011 Valid 21-27 Mar 2011 Forecast from 21 Mar 2011 Valid 21-27 Mar 2011 Observed 20-26 Mar 2011

14. ClimatologyRainy Season Dates ONSET DEMISE

15. Precipitation Climatology

16. Precipitation Climatology Animation