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Recent Evolution and Current Status of the South American Monsoon System

This report provides an update on the recent evolution and current conditions of the South American Monsoon System. It includes information on rainfall patterns, tropical Pacific and Atlantic SST anomalies, atmospheric circulation, and NCEP/GFS model forecasts.

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Recent Evolution and Current Status of the South American Monsoon System

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  1. The South American Monsoon System: Recent Evolution and Current Status Update prepared by Climate Prediction Center / NCEP 3 January 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, drier-than-average conditions were observed over southern Brazil and eastern Argentina. • The GFS predicts below-average rainfall from the western Amazon Basin east-southeastward to Southeast Brazil, and above-average rainfall for the central Amazon Basin and portions of southern Brazil during the next 7 days.

  4. Rainfall Total & Anomaly Patterns:Last 7 Days Total Anomaly During the last 7 days below-average rainfall was observed over portions of southern Brazil, Uruguay and eastern Argentina. Above-average rainfall was observed over portions of southeastern and central Brazil.

  5. Rainfall Totals & Anomaly Patterns:Last 30 Days Total Anomaly During the last 30 days below-average rainfall was observed over western Brazil, Bolivia, northern Paraguay and eastern Argentina. Above-average rainfall was observed over portions of southern and eastern Brazil, southern Paraguay and the western two-thirds of Colombia.

  6. BP Recent Evolution: RainfallLast 90 Days BP: Brazilian Plateau • 90-day rainfall totals remain below average over the southern Amazon Basin. Also, slightly below-average rainfall continues over the core monsoon region (BP). • 90-day totals are near average in southern Brazil, where rainfall during December eliminated previous deficits.

  7. Tropical Pacific and Atlantic SST Anomalies During the last week, equatorial SSTs were between 0.5° - 2.0°C below average over most of the central and eastern Pacific Ocean. SSTs were 0.5°-1.0°C above average in most of the equatorial Atlantic. A La-Nina event is 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 • During 25-31 Dec 2010, weaker-than-average westerlies (easterly anomalies) were observed over central Argentina. • Anomalous rising motion (negative omega) and above-average rainfall (see slide 4 – right panel)were observed over portions of central and southeastern Brazil. 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 (25-31 Dec 2010) above-average temperatures were observed over most of Argentina, while near average temperatures were observed over tropical 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 3 January 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 3 January 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 (3-9 Jan), below-average rainfall is predicted from the western Amazon Basin east-southeastward to Southeast Brazil, while above-average rainfall is predicted for the central Amazon Basin and portions of southern Brazil. • For Days 8-14 (10-16 Jan), above-average rainfall is predicted over the eastern Amazon Basin and portions of southern and southeastern Brazil, while below-average rainfall is predicted over the northern Amazon Basin and east-central Brazil (state of Bahia). . NOTE: See forecast verification in the next slide.

  13. Forecast Verification Forecast from 20 Dec 2010 Valid 27 Dec 2010-2 Jan 2011 Forecast from 27 Dec 2010 Valid 27 Dec 2010-2 Jan 2011 Observed 27 Dec 2010-2 Jan 2011

  14. ClimatologyRainy Season Dates ONSET DEMISE

  15. Precipitation Climatology

  16. Precipitation Climatology Animation

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