1. The South American Monsoon System: Recent Evolution and Current Status
Update prepared by
Climate Prediction Center / NCEP
4 May 2015
For more information, visit:

2. Outline Highlights Recent Evolution and Current Conditions
NCEP/GFS Model Forecasts
Climatology

3. Highlights
Large long-term rainfall deficits continue over the southern Amazon Basin and portions of central Brazil.
During the last 7 days (27 April-3 May 2015), below-average precipitation was observed over northern South America, northern Northeast Brazil, and portions of southern Brazil. Above-average precipitation was observed over east-central Brazil and eastern Argentina.
For May 2015, below-average precipitation is predicted for most of northern South America, northern Northeast Brazil, southern Brazil and northeastern Argentina. Above-average precipitation is indicated for Ecuador, northern Peru, and portions of western and southeastern Brazil.

4. Rainfall Total & Anomaly Patterns: Last 7 Days
During the last 7 days, below-average precipitation was observed over northern South America, northern Northeast Brazil, and portions of southern Brazil. Above-average precipitation was observed over east-central Brazil and eastern Argentina.

5. Rainfall Totals & Anomaly Patterns: Last 30 Days
During the last 30 days, below-average precipitation was observed over portions of the central, eastern and southern Amazon Basin, northeastern Argentina, Uruguay, southern Brazil and northern Northeast Brazil. Above-average precipitation was observed over portions of Ecuador, northern Peru, Paraguay and eastern Argentina.

6. Recent Evolution: Rainfall Last 90 Days
BP: Brazilian Plateau BP
90-day rainfall deficits are present over the southern Amazon Basin (~250 mm) and the western Brazilian Plateau (~130 mm).
90-day rainfall is below average (~150 mm) over southern Brazil.

7. Tropical Pacific and Atlantic SST Anomalies
SSTs are above average in the equatorial Pacific, below average in the low latitudes of the North Atlantic, and above average or near average in the low latitudes of the South Atlantic. (For details concerning El Niño – La Niña, go to the link below.)
A weekly PowerPoint summarizing the ENSO Cycle: Recent Evolution, Current Status and Predictions is available at:

8. Atmospheric Circulation Recent 7 days
Upper panels: During the period of 26 April-2 May 2015, anomalous cyclonic flow (center indicated by red C) was located over the western South Atlantic, with anomalous southerly flow over northern Argentina, Paraguay, Uruguay and southern Brazil.
Lower panels: Anomalous rising motion occurred over the State of Bahia (eastern Brazil) and over eastern Argentina. Anomalous sinking motion occurred over portions of southeastern and southern Brazil. C
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.

9. 925-hPa Wind &Temperature
Recent 30 Days
Recent 7 Days
During the 7-day period 26 April-2 May 2015, above-average temperatures were observed over central Chile, Paraguay and northern Argentina.
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.

10. NCEP/GFS Model Forecasts Bias-Corrected Precipitation
Forecasts from 4 May 2015 – Days 1-7
Total
Anomaly
Note: Bias correction based on last 30-day forecast error.

11. NCEP/GFS Model Forecasts Bias-Corrected Precipitation
Forecasts from 4 May 2015 – Days 8-14
Total
Anomaly
Note: Bias correction based on last 30-day forecast error.

12. NCEP/GFS MODEL FORECASTS
For Days 1-7 (4-10 May 2015), below-average precipitation is predicted for most of northern South America, northern Northeast Brazil, southern Brazil and northeastern Argentina. Above-average precipitation is indicated for Ecuador, northern Peru, and portions of western and southeastern Brazil.
For Days 8-14 (11-17 May 2015), below-average precipitation is indicated for the central and eastern Amazon Basin, southern Peru, southern Brazil and Uruguay. Above –average precipitation is predicted for portions of southern Colombia, Ecuador and northern Peru.

13. Forecast Verification
Forecast from 20 April 2015
Valid for 27 Apr.-3 May 2015
Forecast from 27 April 2015
Valid for 27 Apr.-3 May 2015
Observed 27 Apr.-3 May 2015

14. Climatology Rainy Season Dates
ONSET
DEMISE

15. Precipitation Climatology

16. Precipitation Climatology Animation