The South American Monsoon System: Recent Evolution and Current Status

1. The South American Monsoon System: Recent Evolution and Current Status Update prepared by Climate Prediction Center / NCEP 12 September 2010 For more information, visit:http://www.cpc.ncep.noaa.gov/products/Global_Monsoons/American_Monsoons

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

3. Highlights • Drier-than-average conditions have prevailed over most of Brazil during the last 30 days. • During the next two weeks near- to below-average rainfall is predicted throughout most Brazil.

4. Rainfall Total & Anomaly Patterns:Last 7 Days Total Anomaly During the last 7 days, below-average rainfall was observed over the western and southern Amazon Basin and southern Brazil. Above-average rainfall was observed over portions of northern South America.

5. Rainfall Totals & Anomaly Patterns:Last 30 Days Total Anomaly During the last 30 days below-average rainfall was observed over most of Brazil, with the exception of extreme southern Rio Grande do Sul and coastal areas of the Northeast.

6. BP Recent Evolution: RainfallLast 90 Days BP: Brazilian Plateau • 90-day rainfall totals are below-average over western and west-central Brazil and and portions of southern Brazil.

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

8. Atmospheric Circulation Recent 7 days • During 4-10 September 2010, enhanced 200-hPa anticyclonic circulation (A) was centered over northern Chile. Stronger-than-average westerly flow was observed over central Argentina and stronger-than-average easterly flow was observed throughout the Tropics in the South American sector. • Anomalous sinking motion (positive omega) and dry conditions (see slide 4, left panel) were observed over the western two-thirds of Brazil. A 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 (4-10 September 2010) below-average temperatures were observed over Paraguay, southern Brazil and northeastern Argentina, while above-average temperatures were observed over central Argentina and the central Amazon Basin. 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 12 September 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 12 September 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 (12-18 September), below-average rainfall is predicted over most of Brazil, except for the extreme southern portion of the country (Rio Grande do Sul). • For Days 8-14 (19-25 September), below-average rainfall is predicted to continue over most of Brazil.

13. ClimatologyRainy Season Dates ONSET DEMISE

14. Precipitation Climatology

15. Precipitation Climatology Animation