The South American Monsoon System: Recent Evolution and

Current Status

Update prepared byClimate Prediction Center / NCEP

3 October 2010

For more information, visit:

http://www.cpc.ncep.noaa.gov/products/Global_Monsoons/American_Monsoons

Outline

• Highlights

• Recent Evolution and Current Conditions

• NCEP/GFS Model Forecasts

• Climatology

• Drier-than-average conditions continued over most of the Amazon basin and central Brazil during the last 7 days. Above average rainfall was observed over the state of Mato Grosso do Sul in Brazil, as predicted by the GFS last week.

• During the next two weeks below-average rainfall is predicted to continue over central Brazil.

Highlights

Rainfall Total & Anomaly Patterns:Last 7 Days

During the last 7 days, above-average rainfall was observed over portions southern Brazil (from Mato Grosso do Sul extending to Sao Paulo), while below-average rainfall persisted over most of the Amazon basin.

Total Anomaly

Rainfall Totals & Anomaly Patterns:Last 30 Days

During the last 30 days below-average rainfall was observed over most of Brazil, with the exception of portions of Mato Grosso do Sul state where rainfall was much above average (most of the rainfall was during the last 7 days). Above-average rainfall was also observed over central Argentina and portions of Colombia.

Total Anomaly

BP

Recent Evolution: RainfallLast 90 Days BP: Brazilian Plateau

• 90-day rainfall totals are below-average over western and west-central Brazil. 90-day totals are near-average in southern Brazil.

Tropical Pacific and Atlantic SST Anomalies

During the last week, equatorial SSTs were more than 1°C below-average over most of the central and eastern Pacific Ocean. SSTs were 0.5°-1°C above-average in most of the equatorial Atlantic.

A weekly PowerPoint summarizing the ENSO Cycle: Recent Evolution, Current Status and Predictions is available at: http://www.cpc.noaa.gov/products/precip/CWlink/MJO/enso.shtml

Atmospheric Circulation Recent 7 days

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.

• During 25 Sep – 1 Oct 2010, enhanced anomalous westerly flow was observed over northern Argentina, eastern Paraguay and the states of Mato Grosso do Sul and Sao Paulo in Brazil. Anomalous easterly flow dominated most of South America from 20S northward.

• Anomalous rising motion (negative omega) and wetter-than-average conditions (see slide 4) were observed over southern Brazil (Mato Grosso do Sul and Sao Paulo).

925-hPa Wind &Temperature Recent 30 Days Recent 7 Days

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.

• During the 7-day period (25 Sep – 1 Oct 2010) above-average temperatures were observed over most of Brazil (north of 20S), while slightly below-average temperatures were observed over most of Argentina and Uruguay.

NCEP/GFS Model Forecasts Bias-Corrected Precipitation

Total

Forecasts from 3 October 2010 – Days 1-7

Anomaly

Note:Note: Bias correction based on last 30-day forecast error.

NCEP/GFS Model Forecasts Bias-Corrected Precipitation

Total

Forecasts from 3 October 2010 – Days 8-14

Anomaly

Note:Note: Bias correction based on last 30-day forecast error.

• For Days 1-7 (3-9 October), below-average rainfall is predicted to continue over central and western Brazil. Drier-than-average conditions are also predicted over extreme southern Brazil. Slightly above-average rainfall is predicted for the state of Mato Grosso do Sul in Brazil extending eastward over portions of Southeast Brazil.

• For Days 8-14 (10-16 October), dry than average conditions are expected to continue over central and western Brazil and the extreme South Brazil. Near-average rainfall is predicted for the rest of South America.

NCEP/GFS MODEL FORECASTS

NOTE: See forecast verification in the next slide.

Forecast Verification

Forecast from 19 Sep 2010 Valid 26 Sep – 2 Oct 2010

Forecast from 26 Sep 2010 Valid 26 Sep – 2 Oct 2010

Observed 26 Sep – 2 Oct 2010

ClimatologyRainy Season Dates

ONSETONSET DEMISE

Precipitation Climatology

Precipitation Climatology Animation