1. The South American Monsoon System: Recent Evolution and Current Status
Update prepared by
Climate Prediction Center / NCEP
29 November 2010
For more information, visit:

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

3. Highlights
During the last 7 days, dry conditions persisted over portions of southern Brazil, Uruguay and northeastern Argentina.
The GFS predicts above-average rainfall over Venezuela, Colombia, Paraguay and portions of southern and Southeast Brazil (20-30S) during the next 7 days, while below-average rainfall is predicted for most of northern Argentina during the next two weeks.

4. Rainfall Total & Anomaly Patterns: Last 7 Days
During the last 7 days below-average rainfall was observed over portions of the southern Amazon basin, southwestern and extreme southern Brazil, Uruguay and northeastern Argentina. Above-average rainfall was observed over portions of Southeast and Central Brazil.

5. Rainfall Totals & Anomaly Patterns: Last 30 Days
During the last 30 days below-average rainfall was observed over southern Brazil, Uruguay, and northern Argentina. Above-average rainfall was observed over eastern and central Brazil and the western two-thirds of Colombia. The long-term dry pattern over southeastern South America (southern Paraguay, southern Brazil, Uruguay and northeastern Argentina) is consistent with the ongoing La Nina conditions.

6. Recent Evolution: Rainfall Last 90 Days
BP: Brazilian Plateau BP
90-day rainfall totals remain below average over the southern Amazon Basin. Also, slightly below-average rainfall continues over the core monsoon region (BP). Recently, deficits in these regions have diminished.
90-day totals remain below average in southern Brazil, with deficits of about 100 mm.

7. Tropical Pacific and Atlantic SST Anomalies
During the last week, equatorial SSTs were between 0.5° - 2.0°C below average over most of the central and eastern Pacific Ocean. SSTs were 0.5°-1.5°C above average in most of the equatorial Atlantic. A La-Nina event is in progress in the tropical Pacific (for more details 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
During Nov 2010, anomalous cyclonic circulation (red C) dominated central South America.
Anomalous sinking motion (positive omega) and below-average rainfall were observed over northeastern Argentina and Uruguay. Anomalous rising motion (negative omega) and above-average rainfall (see slide 4 – right panel)
were observed over portions of southeastern Brazil on the northeastern flank of the anomalous cyclonic circulation center. 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 ( Nov 2010) below-average temperatures were observed over most of eastern Bolivia, Paraguay and southern Brazil. Enhanced southerly/ southeasterly flow was observed over that region. The mean position of a cold front during the last 7 days is indicated by the dashed blue line.
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.

10. NCEP/GFS Model Forecasts Bias-Corrected Precipitation
Forecasts from 29 November 2010 – 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 29 November 2010 – Days 8-14
Total
Anomaly
Note: Bias correction based on last 30-day forecast error.

12. NCEP/GFS MODEL FORECASTS
For Days 1-7 (29 Nov-5 Dec), above-average rainfall is predicted over Paraguay, portions of southern and southeastern Brazil (20- 30S), Venezuela and Colombia, while below-average rainfall is predicted for the central and eastern Amazon Basin and Northeast Brazil
For Days 8-14 (6-12 Dec), above-average rainfall is predicted over Northeast Brazil, Venezuela and Colombia, while below-average rainfall is predicted over portions of the southern Amazon Basin, northern Argentina, and southern and southeastern Brazil. .
NOTE: See forecast verification in the next slide.

13. Forecast Verification
Forecast from 14 Nov 2010
Valid Nov 2010
Forecast from 21 Nov 2010
Valid Nov 2010
Observed
22-28 Nov 2010

14. Climatology Rainy Season Dates
ONSET
DEMISE

15. Precipitation Climatology

16. Precipitation Climatology Animation