The South American Monsoon System Recent Evolution and

The South American Monsoon System: Recent Evolution and Current Status Update prepared by Climate Prediction Center / NCEP 2 May 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

Highlights • During the last 7 days, below-average rainfall was observed over central Brazil, while above-average rainfall was observed over southern Brazil. The dipole pattern with dry over central and wet over southern Brazil was well predicted by the GFS last week. • For the next two weeks, the GFS predicts belowaverage rainfall to continue over central Brazil.

Rainfall Total & Anomaly Patterns: Last 7 Days Total Anomaly During the last 7 days, below-average rainfall was observed over the eastern Amazon basin and central Brazil, northern Peru, northeastern Argentina and Uruguay, while above-average rainfall was observed over the western Amazon basin and southern Brazil. The dipole pattern with dry over central Brazil and wet over southern Brazil was well predicted by the GFS last week.

Rainfall Totals & Anomaly Patterns: Last 30 Days Total Anomaly During the last 30 days below-average rainfall was observed over the southwestern Amazon basin southward across most of Bolivia, Paraguay, northeastern Argentina, southern Brazil (Rio Grande do Sul) and Uruguay (red oval), while much above-average rainfall was observed to the north of the dry region and over portions of southern Brazil (blue ovals).

Recent Evolution: Rainfall Last 90 Days BP: Brazilian Plateau CB NB BP BAHIA RJ • 90 -day rainfall totals are belowaverage over central Brazil (CB) and Northeast Brazil (NB). Deficits of about 80 -140 mm. The rainy season in CB apparently ended in early April. • Near-average rainfall totals were observed over southeastern Brazil (RJ), while above-average rainfall totals were observed over Bahia.

Tropical Pacific and Atlantic SST Anomalies During the last week, equatorial SSTs were between 0. 5°C - 1°C above-average across the central and eastern equatorial Pacific Ocean. SSTs were 0. 5°-1. 5°C above-average in the equatorial Atlantic, west of 10°W. A weekly Power. Point 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 • During 24 -30 April 2010, enhanced 200 - h. Pa westerly flow was observed over subtropical latitudes across northern Chile, northern Argentina, Paraguay, Uruguay and Southern Brazil. • Anomalous sinking motion (positive omega) and below-average rainfall (see slide 4) were observed over the northeastern and central Brazil, while rising motion (negative omega) and above-average rainfall were observed over southern Brazil. 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.

925 -h. Pa Wind &Temperature Recent 30 Days Recent 7 Days • During the 7 -day period (24 -30 April 2010) above-average temperatures predominated over Brazil, while below-average temperatures were observed over most of Argentina, Uruguay and extreme southern Brazil. The average location of a cold front during this period 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 -h. Pa are usually similar to surface observations. Note: Areas with surface pressure below 925 -h. Pa are masked out.

NCEP/GFS Model Forecasts Bias-Corrected Precipitation Forecasts from 2 May 2010 – Days 1 -7 Total Note: Bias correction based on last 30 -day forecast error. Anomaly

NCEP/GFS Model Forecasts Bias-Corrected Precipitation Forecasts from 2 May 2010 – Days 8 -14 Total Note: Bias correction based on last 30 -day forecast error. Anomaly

NCEP/GFS MODEL FORECASTS • For Days 1 -7 (2 -8 May), near-average rainfall is predicted over most of Brazil, with the exception of below-average over the central region. Below-average rainfall is also predicted over portions of: Venezuela, Colombia, Ecuador and Peru. • For Days 8 -14 (9 -15 May), dry conditions are predicted to dominated a larger area of South America (most of 5°S 35°S; 80°W-40°W), while above-average conditions are predicted to the northwest of that region (northwestern Amazon basin, Colombia and Venezuela). NOTE: See forecast verification in the next slide.

Forecast Verification Forecast from 18 Apr 2010 Valid 25 Apr – 1 May 2010 Forecast from 25 Apr 2010 Valid 25 Apr – 1 May 2010 Observed 25 Apr – 1 May 2010

Climatology Rainy Season Dates ONSET DEMISE

Precipitation Climatology

Precipitation Climatology Animation