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 2 May 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 most of the areas between 12ºS-8ºN, west of 50ºW (except portions of Colombia and northern Brazil) and over extreme southern Brazil. Above-average rainfall was found over central Argentina, Paraguay, and spotty areas of eastern Brazil. • For 2-8 May, above-average rainfall is predicted for Venezuela, Colombia, and northwestern and northeastern Brazil, and below-average rainfall is predicted for Peru, Bolivia, Paraguay, Uruguay, northeastern Argentina, and a large portion of western, central, and southern Brazil. For 9-15 May, above-average rainfall is predicted for most areas north of 7ºS except over the border area between Colombia and Brazil and for southern portion of Brazil (south of 7ºS), northeastern Brazil, Guyana, Suriname, French Guiana, southern Peru, and southern Bolivia.

4. Rainfall Total & Anomaly Patterns:Last 7 Days Total Anomaly During the last 7 days, below-average rainfall was observed over most of the areas between 12ºS-8ºN, west of 50ºW (except portions of Colombia and northern Brazil) and over extreme southern Brazil. Above-average rainfall was found over central Argentina, Paraguay, and spotty areas of eastern Brazil.

5. Rainfall Totals & Anomaly Patterns:Last 30 Days Total Anomaly During the last 30 days, above-average rainfall was mainly observed over the northwestern and western parts of South America and northeastern and eastern Brazil. Below-average rainfall was observed over Guyana, Suriname, French Guiana, central and southern Brazil, the border areas of Brazil with Colombia and Peru, southern Bolivia, and eastern Argentina.

6. BP Recent Evolution: RainfallLast 90 Days BP: Brazilian Plateau • 90-day rainfall totals are below average over the southern Amazon Basin and near normal over the core monsoon region (BP). • 90-day totals are above 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 • Upper panels: During 23-29 Apr 2011, an anomalous cyclonic (C) pattern and an anomalous anti-cyclonic (A) pattern were observed in the upper troposphere over southern Brazil and subtropical Atlantic Ocean, respectively. • Lower panels: Weak anomalous rising motion (negative omega) was observed over the western South America and parts of northern and southern Brazil, and weak anomalous sinking motion was seen over Suriname and portions of northwestern, eastern, and extreme southern Brazil. A C 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 (23-29 Apr 2011), above-average temperatures occurred over northeastern Argentina and southwestern Brazil. 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 2 May 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 2 May 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 (2-8 May), above-average rainfall is predicted for Venezuela, Colombia, and northwestern and northeastern Brazil, and below-average rainfall is predicted for Peru, Bolivia, Paraguay, Uruguay, northeastern Argentina, and a large portion of western, central, and southern Brazil. • For Days 8-14 (9-15 May), above-average rainfall is predicted for most areas north of 7ºS except over the border area between Colombia and Brazil and for southern portion of Brazil (south of 7ºS), northeastern Brazil, Guyana, Suriname, French Guiana, southern Peru, and southern Bolivia.

13. Forecast Verification Forecast from 18 Apr2011 Valid 25 Apr – 1 May 2011 Forecast from 25 Apr 2011 Valid 25 Apr – 1 May 2011 Observed 25 Apr – 1 May 2011

14. ClimatologyRainy Season Dates ONSET DEMISE

15. Precipitation Climatology

16. Precipitation Climatology Animation