The South American Monsoon System: Recent Evolution and

Current Status

Update prepared byClimate Prediction Center / NCEP

28 April 2014

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

• Large rainfall deficits persist over the SAMS core region (Brazilian Plateau).

• During the last 7 days (21-27 April 2014), below-average precipitation was observed over coastal areas of northeastern South America, southern Brazil, Uruguay and eastern Argentina, and above-average precipitation was observed over northern Paraguay, eastern Bolivia and portions of the western Amazon Basin.

• For 28 April-4 May 2014, below-average precipitation is predicted for the southern Amazon Basin and southeastern Brazil, and above-average precipitation is southern Chile, Paraguay, extreme northeastern Argentina and portions of southern Brazil.

Highlights

Rainfall Total & Anomaly Patterns:Last 7 Days

During the last 7 days, below-average precipitation was observed over coastal areas of northeastern South America, southern Brazil, Uruguay and eastern Argentina, and above-average precipitation was observed over northern Paraguay, eastern Bolivia and portions of the western Amazon Basin.

Total Anomaly

Rainfall Totals & Anomaly Patterns:Last 30 Days

During the last 30 days, below-average precipitation was observed over the eastern and southern Amazon Basin, Venezuela, western Colombia and Ecuador. Above-average precipitation was observed over southern Paraguay and most of Argentina.

Total Anomaly

BP

Recent Evolution: RainfallLast 90 Days BP: Brazilian Plateau

• 90-day rainfall deficits (100-300 mm) continue over the Brazilian Plateau and the southern Amazon Basin.

• 90-day rainfall totals are near average over southern Brazil.

Tropical Pacific and Atlantic SST Anomalies

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

SSTs are above average in most of the equatorial Pacific. SSTs are near average in most of the equatorial Atlantic. (For details concerning El Niño – La Niña, go to the link below.)

Atmospheric Circulation Recent 7 days

• Upper panels: During the period of 19-25 April 2014, anomalous cyclonic circulation was observed over the western Atlantic near 35S (red C).

• Lower panels: Areas of anomalous rising motion were found over Bolivia, northern Paraguay and southern Brazil, while anomalous sinking motion, a proxy for suppressed precipitation, was observed over Chile, most of Argentina, and Uruguay.

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.

C

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

Low-level (~600 m above sea level) 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 19-25 April 2014, below-average temperatures were observed over eastern Argentina, Uruguay, and southern Brazil.

NCEP/GFS Model Forecasts Bias-Corrected Precipitation

Total

Forecasts from 28 Apr 2014– 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 28 Apr 2014– Days 8-14

Anomaly

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

• For Days 1-7 (28 Apr-4 May 2014), below-average precipitation is predicted for the southern Amazon Basin and southeastern Brazil, and above-average precipitation is southern Chile, Paraguay, extreme northeastern Argentina and portions of southern Brazil.

• For Days 8-14 (5-11 May 2014), below-average precipitation is predicted for the southern Amazon Basin and southeastern Brazil, and above-average precipitation northern Northeast Brazil, southern Paraguay, and eastern Argentina.

NCEP/GFS MODEL FORECASTS

Forecast Verification

Forecast from 14 Apr 2014Valid for 21-27 Apr 2014

Forecast from 21 Apr 2014 Valid for 21-27 Apr 2014 Observed 21-27 Apr 2014

ClimatologyRainy Season Dates

ONSETONSET DEMISE

Precipitation Climatology

Precipitation Climatology Animation