The South American Monsoon System: Recent Evolution and Current Status

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The South American Monsoon System Recent
Evolution and Current Status
Update prepared by Climate Prediction Center / NC
EP
4 April 2008
For more information, visit http//www.cpc.ncep.
noaa.gov/products/Global_Monsoons/American_Monsoon
s

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Outline

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

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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 continue over the southern
Amazon, Central, southeastern and portions of
southern Brazil. Below-normal rainfall was also
observed over northern Colombia, northeastern
Argentina, and western Uruguay.
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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
northern Brazil. Below-normal rainfall was
observed over the southern Amazon, southern and
portions of central/southeastern Brazil, northern
Colombia, northeastern Argentina and most of
Uruguay.
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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 the southern Amazon, northern Colombia,
southeastern and southern Brazil, northeastern
Argentina, and Uruguay.
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Rainfall Patterns Last 7 Days
During the last 7 days rainfall was above normal
over the eastern Amazon, northeastern Brazil,
Peru, Paraguay and northwestern Argentina.
Below-normal rainfall was observed over the
northwestern Amazon, southeastern Brazil, and
northeastern Argentina.
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Atmospheric Circulation Recent 7 days

• During 26 March 01 April March the 200-hPa
  Bolivian Anticyclone was located in its normal
  position (A in top-left panel).
  
• An enhanced trough was centered over eastern
  Brazil (thick dashed line in top-right panel).
  
• This trough contributed to mean and anomalous
  upward motion (negative omega) over Northeast
  Brazil (bottom panels).

A
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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 near normal In
  central Brazil.
  
• Rainfall has been below normal in portions of
  southern Brazil and northeastern Argentina.

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NCEP/GFS Model Forecasts Bias-Corrected
Precipitation
Week 1 (5-11 April 2008)
10
NCEP/GFS Model Forecasts Bias-Corrected
Precipitation
Week 2 (12-18 April 2008)
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Summary

• During the last 30 days rainfall has been above
  normal over the Northeast Brazil, Ecuador,
  northern Peru and southern Colombia.
  
• Long-term rainfall deficits of up to 400 mm
  remain over portions of central, southeastern,
  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 the
  northeastern, central and southeastern Brazil in
  week 1 (5-11 Apr 2008). Below-normal rainfall is
  predicted for the southwestern Amazon Basin,
  Bolivia, Paraguay, northeastern Argentina,
  Uruguay and southern Brazil.
• For week 2 (12-18 April 2008) above-normal
  rainfall is predicted over central and eastern
  Amazon, northeastern and southern Brazil.
  Drier-than-normal conditions are indicated for
  northern South America.
• 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.

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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 Functio
n) correction is made for each forecast
- For each individual forecast and each grid p
oint, cumulative PDFs for both forecasts and
observations (CMORPH) are defined using values of
the past 35 days within 15X15 boxes.
- GFS forecasts are replaced by observations at
the same percentile level of the cumulative
PDFs. 3. Forecast anomalies are taken as the di
fferences of the bias-corrected ensemble mean
from the 2003-2006 CMORPH average.
4. Week-1 forecast is at 1-day lead and week-2 f
orecast is at 8-day lead.
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ClimatologyRainy Season Dates
ONSET
DEMISE
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Precipitation Climatology