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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 26 November 2007. Outline. Recent Evolution and Current Conditions Summary Climatology. Rainfall Patterns: Last 30 Days.

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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 26 November 2007

  2. Outline • Recent Evolution and Current Conditions • Summary • Climatology

  3. Rainfall Patterns: Last 30 Days Below-normal rainfall has been observed over most of Brazil, except for the western Amazon Basin and the southern portion of the country. Below-normal rainfall was also observed over Uruguay and northern Argentina.

  4. Rainfall Patterns: Last 90 Days Below-normal rainfall has been observed over most of Brazil, with rainfall deficits of more than 175 mm in central Brazil. Slightly above-normal rainfall was observed ove eastern Bolivia, Paraguay and extreme southern Brazil.

  5. BP Recent Evolution: Rainfall • The SAMS wet season was delayed in many areas. • Recently, seasonal-to-date rainfall has increased to near normal in western Brazil, but rainfall deficits continue over the Brazilian Plateau (BP), with deficits around 150 mm during the last 3 months.

  6. Recent Evolution: OLR • During 23 October-1 November (top panel) enhanced precipitation (negative OLR anomalies) was observed over portions of southeastern and southern Brazil. Positive OLR anomalies (drier-than-average conditions) covered most of the Amazon Basin, Northeast Brazil, and central Argentina. • During 2-11 November, wetter-than normal conditions strengthened over southeastern Brazil, while drier-than-normal conditions continued over Northeast Brazil. • During 12-21 November drier-than-normal conditions dominated central and Northeast Brazil, while slightly wetter-than-normal conditions were observed over Southeast Brazil.

  7. Atmospheric Circulation & OLR Last 5 days • During the last 5 days low OLR (left panel) was observed from the western Amazon southeastward across southeastern Brazil and over the western South Atlantic Ocean. • However, precipitation was generally below normal (positive OLR anomalies, right panel) over all of Brazil and most of Argentina. • During this period an amplified 200-hPa ridge was located over northern Argentina and southern Brazil.

  8. Summary • Season-to-date rainfall has been near normal in western Brazil. • The rainy season has been slow to start over central and southeastern Brazil. • During the last 90 days, rainfall deficits of ~150 mm have been observed over portions of central and southeastern Brazil.

  9. ONSET DEMISE ClimatologyRainy Season Dates

  10. Precipitation Climatology

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