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The South American Monsoon System: Recent Evolution and Current Status

This report provides an update on the recent evolution and current conditions of the South American Monsoon System, including information on rainfall patterns and anomalies, tropical Pacific and Atlantic SST anomalies, atmospheric circulation, and forecast predictions.

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The South American Monsoon System: Recent Evolution and Current Status

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  1. The South American Monsoon System: Recent Evolution and Current Status Update prepared by Climate Prediction Center / NCEP 6 September 2009 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 • The increased frequency of cold fronts over southeastern South America contributed to above-average rainfall over southern Brazil during the last week. • The GFS predicts that above-normal rainfall will continue over southern Brazil and southern Paraguay during the next week.

  4. Rainfall Total & Anomaly Patterns:Last 7 Days Total Anomaly During the last 7 days above-average rainfall was observed over southern Brazil, northern Uruguay and portions of northeastern Argentina. Below-average rainfall was observed over the northern Amazon basin, most of Venezuela and eastern Colombia.

  5. Rainfall Totals & Anomaly Patterns:Last 30 Days Total Anomaly During the last 30 days much above-average rainfall was observed over southern Brazil, while much below-average rainfall was observed over Venezuela, Suriname and the Guianas.

  6. BP Recent Evolution: RainfallLast 90 Days BP: Brazilian Plateau NCA CB SA SB • 90 days rainfall totals are above-average for the southern Amazon basin (SA), southern Brazil (SB) and central Brazil (CB), and near-normal over the north-central Amazon basin (NCA).

  7. Tropical Pacific and Atlantic SST Anomalies During the last week, equatorial SSTs were at least 0.5°C above-average across the Pacific Ocean and at least 1.0°C above average over the central and eastern Pacific near the northern South American coast. SSTs were below average in the Tropical Atlantic near the South American coast extending eastward to the African coast.

  8. Atmospheric Circulation Recent 7 days • During 29 Aug - 4 Sep, an enhanced 200-hPa anticyclonic circulation was centered near the southern Brazil coast, while enhanced cyclonic circulation was centered near the coast of Chile. • Anomalous rising motion (negative omega) and above-normal rainfall (see slide 4) were observed over southern Brazil, northern Uruguay and portions of northeastern Argentina. C 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 (29 Aug – 4 Sep 2009) above-normal temperatures and enhanced northerly flow were observed over southern Brazil, Paraguay, Uruguay and northeastern Argentina (left-panel black circle). 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 September 2009 – 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 September 2009 – 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 Sep 2009), above-average rainfall is predicted over southern Brazil and southern Paraguay, while below-average rainfall is expected over the northwestern Amazon Basin, and most of Venezuela and Colombia. • For Days 8-14 (13-19 Sep 2009), below-average rainfall is predicted over most of the Amazon Basin and Venezuela, and slightly above-average rainfall is expected over portions of southern Brazil, Uruguay and northeastern Argentina. NOTE: See forecast verification in the next slide.

  13. Forecast Verification Forecast from 23 Aug 2009 Valid 30 Aug – 5 Sep 2009 Forecast from 30 Aug 2009 Valid 30 Aug – 5 Sep 2009 Observed Valid 30 Aug – 5 Sep 2009 NOT AVAILABLE

  14. ClimatologyRainy Season Dates ONSET DEMISE

  15. Precipitation Climatology

  16. Precipitation Climatology Animation

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