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 6 September 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, below-average rainfall was observed over northern South America (around and to the north of the equator). During the last 30 days, below-average rainfall was observed over much of northern South America (north of 10ºS), northern Bolivia, southwestern Brazil, and northeastern Argentina, and above-average rainfall was found over extreme southern Brazil. • For 6-12 September, above-average rainfall is predicted for Colombia, Peru, eastern Paraguay, and portions of southern Brazil. Below-average rainfall is predicted over eastern Venezuela, portions of central Brazil, northeastern Argentina, Uruguay, and extreme southern Brazil. For 13-19 September, below-average rainfall is predicted for much of central and northern South America. Above-average rainfall is predicted over northeastern Venezuela, portions of northern Colombia, portions of southern Peru, and Uruguay.

4. Rainfall Total & Anomaly Patterns:Last 7 Days Total Anomaly During the last 7 days, below-average rainfall was observed over northern South America (around and to the north of the equator).

5. Rainfall Totals & Anomaly Patterns:Last 30 Days Total Anomaly During the last 30 days, below-average rainfall was observed over much of northern South America (north of 10ºS), northern Bolivia, southwestern Brazil, and northeastern Argentina. Above-average rainfall was found over extreme southern Brazil.

6. BP Recent Evolution: RainfallLast 90 Days BP: Brazilian Plateau • 90-day rainfall totals are clearly below average over the southern Amazon Basin, and the Brazilian Plateau. • 90-day totals are above average in southern Brazil.

7. Tropical Pacific and Atlantic SST Anomalies Overall, slightly below-average SSTs were observed in the equatorial Pacific Ocean. SSTs were slightly above average in the equatorial Atlantic. (For more details of El Niño – La Niña evolutions, 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 28 Aug – 3 Sept 2011, an anomalous anticyclonic circulation (A) was observed in the upper troposphere over northern Chile/Argentina. • Lower panels: Weak anomalous sinking motion (positive omega) was observed over northern and central South America, and anomalous rising motion was observed over southern South America and the nearby eastern Pacific Ocean. 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 28 August – 3 September 2011, above-average temperatures occurred over northern South America especially over central Brazil. Below-average temperatures were found over extreme southern Brazil and Uruguay. 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 6 Sept 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 6 Sept 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 (6-12 September), above-average rainfall is predicted for Colombia, Peru, eastern Paraguay, and portions of southern Brazil. Below-average rainfall is predicted over eastern Venezuela, portions of central Brazil, northeastern Argentina, Uruguay, and extreme southern Brazil. • For Days 8-14 (13-19 September), below-average rainfall is predicted for much of central and northern South America. Above-average rainfall is predicted over northeastern Venezuela, portions of northern Colombia, portions of southern Peru, and Uruguay.

13. Forecast Verification Forecast from 22 Aug 2011 Forecast from 29 Aug 2011 Observed 29 Aug – 4 Sep 2011 Unavailable Unavailable

14. ClimatologyRainy Season Dates ONSET DEMISE

15. Precipitation Climatology

16. Precipitation Climatology Animation