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The South American Monsoon System: Recent Evolution and Current Status

The South American Monsoon System: Recent Evolution and Current Status. Update prepared by Climate Prediction Center / NCEP 18 April 2008. For more information, visit: http://www.cpc.ncep.noaa.gov/products/Global_Monsoons/American_Monsoons. Outline. Recent Evolution and Current Conditions

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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 18 April 2008 For more information, visit:http://www.cpc.ncep.noaa.gov/products/Global_Monsoons/American_Monsoons

  2. Outline • Recent Evolution and Current Conditions • NCEP/GFS Model Forecasts • Summary • Climatology

  3. Rainfall Patterns: Last 180 Days During the last 180 days above-normal rainfall was observed over central/southern Colombia, Ecuador, Peru, northern Chile, Bolivia, Paraguay, northern Brazil, Suriname and Guyana. Below normal rainfall was observed over the southern Amazon, Central, southeastern and portions of southern Brazil. Below-normal rainfall was also observed over northern Colombia, northeastern Argentina, and Uruguay.

  4. Rainfall Patterns: Last 90 Days During the last 90 days above-normal rainfall was observed over northern Chile, northwestern Argentina, Bolivia, northern/central Paraguay, Peru, Ecuador, southern/central Colombia and eastern third of Brazil. Below-normal rainfall was observed over northern Colombia, southern/central Amazon, southern Brazil, northeastern Argentina and most of Uruguay.

  5. Rainfall Patterns: Last 30 Days During the last 30 days much above-normal rainfall was observed over the eastern Amazon and northeastern Brazil. Above normal rainfall was also observed over southern Colombia, Ecuador and northern Peru. Below-normal rainfall was observed over northern Colombia, northwestern and southern Amazon, portions of southern Brazil, northeastern Argentina, and Uruguay.

  6. Rainfall Patterns: Last 7 Days During the last 7 days rainfall was above normal over portions of southern Brazil. Below-normal rainfall was observed over the northwestern and southern Amazon. Near-normal rainfall was observed over the rest of South America.

  7. Atmospheric Circulation Recent 7 days • During 9-15 April an enhanced 200-hPa anticyclone circulation was centered near the coastal areas of southeastern Brazil (A in top-right panel). • This circulation was associated with mean and anomalous upward motion (negative omega) on its western flank over Southern Brazil and Paraguay (regions indicated in bottom panels). A

  8. Recent Evolution: Rainfall • During the last 90 days rainfall has been above normal over Ecuador/ northern Peru, and Northeast Brazil. • 90-day rainfall totals are slightly above normal in central Brazil. • Rainfall has been below normal in portions of southern Brazil and northeastern Argentina.

  9. NCEP/GFS Model Forecasts Bias-Corrected Precipitation Week 1 (19-25 April 2008)

  10. NCEP/GFS Model Forecasts Bias-Corrected Precipitation Week 2 (26 Apr-2 May 2008)

  11. Summary • During the last 30 days rainfall has been above normal over the eastern Amazon and northeastern Brazil, Ecuador, northern Peru and southern Colombia. • Long-term rainfall deficits of up to 400 mm remain over portions of central and southeastern Brazil, and deficits between 100 mm and 200 mm remain over portions of southern Brazil and northeastern Argentina. NCEP/GFS MODEL FORECASTS • Above-normal precipitation is predicted for most of the Amazon Basin, and portion of southeastern Brazil in week 1 (19-25 Apr 2008). • For week 2 (26 Apr- 2 May 2008) above-normal rainfall is predicted over the eastern third of Brazil. Drier-than-normal conditions are indicated for Venezuela, Suriname, Guyana, southern Brazil, Uruguay and eastern Argentina. • Note: Due to a wet bias in CMORPH the area of wetter-than-normal conditions is likely to be greater and the area of drier-than-normal conditions is likely to be less than depicted in slides 9 and 10.

  12. Forecasts VerificationPeriod between: 12-18 April 2008 4 April 2008 9 April 2008 Observed NOTE: The week 1 forecast from 9Apr2008 is used because the forecast from 11Apr2008 is missing.

  13. Information About the NCEP/GFS Model Forecasts • 1.The forecast uses four operational NCEP/GFS forecast runs from 00Z, 06Z, 12Z, and 18Z initial conditions. • 2. PDF (Probability Density Function) correction is made for each forecast: • - For each individual forecast and each grid point, cumulative PDFs for both forecasts and observations (CMORPH) are defined using values of the past 35 days within 15°X15° boxes. • - GFS forecasts are replaced by observations at the same percentile level of the cumulative PDFs. • 3. Forecast anomalies are taken as the differences of the bias-corrected ensemble mean from the 2003-2006 CMORPH average. • 4. Week-1 forecast is at 1-day lead and week-2 forecast is at 8-day lead.

  14. ClimatologyRainy Season Dates ONSET DEMISE

  15. Precipitation Climatology

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