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 23 April 2012 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 precipitation was observed mainly over Colombia Ecuador, and northern Peru. Below-average rainfall occurred over northern, central, and extreme southern Brazil and Uruguay. • For 22-28 Apr 2012, above-average precipitation is predicted for central Colombia, northern Peru, northeastern Paraguay, and portions of northwestern and southern Brazil. Below-average precipitation is predicted for southern Venezuela, Guyana, northern and extreme southern Brazil, southern Peru, Bolivia, and northeastern Argentina. • For 29 Apr – 5 May 2012, above-average precipitation is predicted for regions north of the equator, northwestern Brazil, Ecuador, and northern Peru. Below-average precipitation is predicted for much of Brazil, southern Peru, Bolivia, eastern Argentina, and Uruguay.

4. Rainfall Total & Anomaly Patterns:Last 7 Days Total Anomaly During the last 7 days, above-average precipitation was observed mainly over Colombia Ecuador, and northern Peru. Below-average rainfall occurred over northern, central, and extreme southern Brazil and Uruguay.

5. Rainfall Totals & Anomaly Patterns:Last 30 Days Total Anomaly During the last 30 days, above-average rainfall was observed over Colombia, Ecuador, northern Peru, portions of Brazil, and Paraguay. Below-average rainfall occurred over most of the remainder of South America especially northeastern Brazil.

6. BP Recent Evolution: RainfallLast 90 Days BP: Brazilian Plateau • 90-day rainfall totals are clearly below average over the southern Amazon basin, the Brazilian Plateau (core monsoon region), and southern Brazil.

7. Tropical Pacific and Atlantic SST Anomalies Above-average SSTs are observed in the tropical eastern Pacific and below-average SSTs are present in the equatorial central Pacific and most of the equatorial Atlantic Ocean. (For more details concerning El Niño – La Niña, 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 the period of 14-20 April 2012, anomalous upper-tropospheric anticyclonic circulation (red A) affected much of South America, centered at 25S/65W. Confluent and diffluent flows occurred over eastern Brazil and northwestern Brazil, respectively. • Lower panels: Anomalous rising motion (negative omega) occurred over northwestern and western South America. Anomalous sinking motion was observed over central-eastern Brazil. A 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 7-day period of 14-20 April 2012, temperatures were above average over central-southern Brazil (10S-25S) and eastern Argentina. 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 23 April 2012 – 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 23 April 2012 – Days 8-14 Total Anomaly Note: Bias correction based on last 30-day forecast error.

12. NCEP/GFS MODEL FORECASTS • For Days 1-7 (22-28 Apr 2012), above-average precipitation is predicted for central Colombia, northern Peru, northeastern Paraguay, and portions of northwestern and southern Brazil. Below-average precipitation is predicted for southern Venezuela, Guyana, northern and extreme southern Brazil, southern Peru, Bolivia, and northeastern Argentina. • For Days 8-14 (29 Apr – 5 May 2012), above-average precipitation is predicted for regions north of the equator, northwestern Brazil, Ecuador, and northern Peru. Below-average precipitation is predicted for much of Brazil, southern Peru, Bolivia, eastern Argentina, and Uruguay.

13. Forecast Verification Forecast from 9 April 2012 Valid 15-21 Apr 2012 Forecast from 16 Apr 2012 Valid 15-21 Apr 2012 Observed 15-21 Apr 2012 Not available Not available

14. ClimatologyRainy Season Dates ONSET DEMISE

15. Precipitation Climatology

16. Precipitation Climatology Animation