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 /
NCEP 13 December 2008
For more information, visit http//www.cpc.ncep.
noaa.gov/products/Global_Monsoons/American_Monsoon
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Outline

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

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Highlights

• During the last 30 days, rainfall deficits
  decreased over Central and Southeast Brazil, as
  an enhanced South Atlantic Convergence Zone
  (SACZ) brought above normal rainfall to the
  region.

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Rainfall Anomaly Patterns
Last 90 Days
Last 30 Days
Last 7 Days
Long-term rainfall deficits over the southern
Amazon, central and southeastern Brazil
decreased during the last 30 days. Much above
normal rainfall was observed over coastal
southeastern Brazil. During the last 7 days
below-normal rainfall was observed over
southeastern and central-western Brazil.
Long-term (90 30 days) rainfall deficits are
evident over Uruguay and eastern Argentina.
NOTE Due to a lack of station reports, the
rainfall deficits over northern Colombia and
southern Venezuela are not real (red circle).
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Recent Evolution Rainfall

• 90-day rainfall totals are below normal in the
  southern Amazon (deficits between 100-180 mm).
• 90-day rainfall totals are near normal over
  portions of the Brazilian Planalto (BP) and
  southeastern Brazil (near Rio de Janeiro)

BP
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Atmospheric Circulation Recent 7 days

• During 5-11 Dec an anomalously strong 200-hPa
  trough (heavy dashed line) was located over the
  western Atlantic, with anomalous downward motion
  (positive omega) observed to the west of the
  trough axis from the southern Amazon basin to
  southeastern Brazil. These features are
  consistent with dry conditions observed in that
  region (see slide 4).

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925-hPa Temperature
Recent 90 Days
Recent 30 Days
Recent 7 Days

• During the last 7 days (5-11 Dec 2008),
  near-normal temperatures were observed over most
  of South America, with the exception of slightly
  below-normal temperatures over the southeastern
  Brazil coast.

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NCEP/GFS Model Forecasts Bias-Corrected
Precipitation
Forecasts from 13 December 2008
Week 1
Week 2
Note Bias correction based on last 30-day
forecast error.
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NCEP/GFS MODEL FORECASTS

• For week 1 (13-19 Dec2008), above normal rainfall
  is forecasted for central and southeastern
  Brazil, associated with an enhanced South
  Atlantic Convergence Zone (SACZ). Below-normal
  rainfall is predicted for the western Amazon
  basin, southern Brazil, Paraguay, northern
  Argentina and Uruguay.
• For week 2 (20-26 Dec 2008) below-normal rainfall
  is predicted over most of the Amazon Basin and
  central-western Brazil and Paraguay.

NOTE See forecast verification in the next slide.
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Forecast Verification
Forecast from 5 Dec 2008 Valid 5-11 Dec 2008
Observed 6 Nov 12 Dec 2008
Forecast from 28 Nov 2008 Valid 5-11 Dec 2008
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ClimatologyRainy Season Dates
ONSET
DEMISE
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Precipitation Climatology