1. The South American Monsoon System: Recent Evolution and Current Status Update prepared by Climate Prediction Center / NCEP 18 April 2011 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. During the last 7 days, below-average rainfall was observed over central and portions of Southeast Brazil, French Guiana, Suriname, and most of Guyana. Above-average rainfall was observed over most of southern Brazil, Ecuador, Colombia and Venezuela. For Days 1-7 (18-24 Apr), above-average rainfall is predicted for the northern Amazon Basin, and below-average rainfall is predicted for central and southeastern Brazil. For Days 8-14 (25 Apr-1 May), above- average rainfall is predicted for northeastern South America from Venezuela southeastward to northern Northeast Brazil, and over western Brazil and northern Peru. Highlights

4. Rainfall Total & Anomaly Patterns: Last 7 Days During the last 7 days, below-average rainfall was observed over central and portions of Southeast Brazil, French Guiana, Suriname, and most of Guyana. Above-average rainfall was observed over most of southern Brazil, Ecuador, Colombia and Venezuela. TotalAnomaly

5. Rainfall Totals & Anomaly Patterns: Last 30 Days During the last 30 days, above-average rainfall was observed over most of the northern and western Amazon Basin, northern and southern Peru, and portions of southern Brazil. Below-average rainfall was observed over portions of northern Northeast Brazil, Suriname, French Guiana and the northern two-thirds of Argentina. TotalAnomaly

6. BP Recent Evolution: Rainfall Last 90 Days BP: Brazilian Plateau 90-day rainfall totals are above average over the southern Amazon Basin and the core monsoon region (BP). 90-day totals are above near average in southern Brazil.

7. Tropical Pacific and Atlantic SST Anomalies During the last week, equatorial SSTs were 0.5° - 1.0°C below average over the central Pacific Ocean. SSTs were 0.5° - 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 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 2-8 Apr 2011, anomalous cyclonic flow (red C) was observed in the upper troposphere over northern Argentina, Paraguay, Uruguay and southern Brazil. Lower panels: Anomalous rising motion (negative omega) was observed over Bolivia and southeastern Brazil where rainfall was above average (see Slide 4), and anomalous sinking motion was seen over central Brazil where rainfall was below average. C

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 last 7-day period (26 Mar-1 Apr 2011), near-average temperatures were observed over most of South America.

10. NCEP/GFS Model Forecasts Bias-Corrected Precipitation Total Forecasts from 18 April 2011 – 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 18 April 2011– Days 8-14 Anomaly Note: Note: Bias correction based on last 30-day forecast error.

12. For Days 1-7 (18-24 Apr), above-average rainfall is predicted for the northern Amazon Basin, and below-average rainfall is predicted for central and southeastern Brazil. For Days 8-14 (25 Apr-1 May), above-average rainfall is predicted for northeastern South America from Venezuela southeastward to northern Northeast Brazil, and over western Brazil and northern Peru. NCEP/GFS MODEL FORECASTS

13. Forecast Verification Forecast from 4 Apr2011 Valid 11-17 Apr 2011 Forecast from 11 Apr 2011 Valid 11-17 Apr 2011 Observed 11-17 Apr 2011

14. Climatology Rainy Season Dates ONSETDEMISE

15. Precipitation Climatology

16. Precipitation Climatology Animation