1. The South American Monsoon System Summary September 2012-May 2013 Prepared June 2013 by Climate Prediction Center / NCEP In collaboration with Instituto Nacional de Meteorologia (INMET) and Centro de Previsão de Tempo e Estudos Climáticos (CPTEC) For more information, visit: http://www.cpc.ncep.noaa.gov/products/Global_Monsoons/American_Monsoons http://www.cpc.ncep.noaa.gov/products/Global_Monsoons/American_Monsoons

2. Summary The rainy season onset phase (SON) featured rainfall deficits of 200-400 mm or more over parts of the Amazon basin, central and southern Brazil. Above- average rainfall was observed over central Colombia, portions of Peru, Paraguay and eastern Argentina. ENSO-neutral conditions were present in the tropical Pacific. During the mature phase of the monsoon (DJF) rainfall was below average over central, Northeast and most of Southeast Brazil, eastern Bolivia and northern Argentina, with rainfall deficits greater than 300 mm in many areas. Above- average rainfall was observed over portions of Colombia, northwestern Brazil, Peru, Uruguay and extreme southern Brazil. ENSO-neutral conditions continued in the tropical Pacific. During the decay phase of the rainy season (MAM), rainfall was below average over western, northeastern and southern Brazil, Venezuela, and northern Argentina, with deficits greater than 300 mm observed over portions of those regions. Above-average rainfall was observed over central Colombia, Paraguay and portions of the central Amazon basin in Brazil. SST’s were near average throughout most of the equatorial Pacific. In general, rainfall deficits were observed over most of South America during September 2012-May 2013, with the core monsoon region (Brazilian Plateau) experiencing the largest deficit in the historical record (1979-2013).

3. Outline Onset phase Mature phase Decay phase Long-Term Departures from Average Summary

4. Selected Regions in South America SAMS core region – Brazilian Plateau (BP) Northern Northeast Brazil (NNE) Southern Northeast Brazil (SNE)

5. Precipitation Climatology ONSET DATES

6. Precipitation Departures: Onset Phase (Sep-Nov 2012) During September-November 2012 rainfall was below average over most of western, central-western and southern Brazil, with rainfall deficits exceeding 300 mm in parts of the Amazon basin. Above-average rainfall was observed over central Colombia, portions of Peru, Paraguay and eastern Argentina.

7. SON Historical Time Series for BP Region 1981-2010 mean

8. Tropical Pacific and Atlantic SST Anomalies (Sep-Nov 2012) During September–November 2012, equatorial SSTs were 0.5-1°C above average over the central Pacific Ocean (150°E-150°W). In the tropical Atlantic, SSTs were above average from northern South America to the West coast of North Africa. Negative SST anomalies were observed in the subtropical South Atlantic Ocean.

9. Precipitation Departures: Mature Phase (Dec 2012-Feb 2013) During December 2012-February 2013 rainfall was below average over central, Northeast and most of Southeast Brazil, eastern Bolivia and northern Argentina, with rainfall deficits greater than 300 mm in many areas. Above-average rainfall was observed over portions of Colombia, northwestern Brazil, Peru, Uruguay and extreme southern Brazil.

10. DJF Historical Time Series for BP Region 1981-2010 mean

11. Tropical Pacific and Atlantic SST Anomalies (Dec12-Feb13) During December 2012–February 2013, negative SST anomalies developed in the central and eastern equatorial Pacific and positive SST anomalies remained in the western equatorial Pacific. Over the Atlantic equatorial, SSTs were slightly above average from northern South America to the African coast, and along the African coast south of the equator. Small negative anomalies remained in the subtropical South Atlantic.

12. Precipitation Climatology END DATES

13. Precipitation Departures: Decay Phase (Mar-May 2013) During March-May 2013 rainfall was below average over portions of western, northeastern and southern Brazil, Venezuela, and northern Argentina, with deficits greater than 300 mm observed over portions of those regions. Above-average rainfall was observed over central Colombia, Paraguay and portions of the central Amazon basin in Brazil.

14. MAM Historical Time Series for BP Region 1981-2010 mean

15. Tropical Pacific and Atlantic SST Anomalies (Mar-May 2013) During March-May 2013, equatorial SSTs were near average in the Pacific Ocean, except in the far western portions on the basin and along the immediate West Coast of South America. In the tropical Atlantic, SSTs were above average north of the equator and near or slightly above average south of the equator.

16. Precipitation Departures: September 2012- May 2013 During September 2012 - May 2013 rainfall was below average throughout most of Brazil, Venezuela, eastern Bolivia and northern Argentina, and above average over central Colombia, eastern Ecuador and northern Peru.

17. SONDJFMAM Historical Time Series for BP Region 1981-2010 mean

18. Northeast Brazil Drought Interior Northeast Brazil suffered its second consecutive year of severe drought. During February-April 2012 rainfall was less than 50% of the average in many areas. Similar conditions occurred in northern NE Brazil (NNE) during February-April 2013, while in southern NE Brazil (SNE) drought conditions continued although not as severe as during the previous year (see next slide).

19. February-April Historical Time Series 1981-2010 mean In NNE and SNE FMA 2012 and FMA 2013 rank amongst the driest FMA periods during 1979-2013.

20. Northern Northeast Brazil (NNE) Stations Rainfall deficits are indicated in red. Data Source: INMET Courtesy of Mozar Salvador & Fabricio Silva

21. Rainfall deficits are indicated in red. Data Source: INMET Courtesy of Mozar Salvador & Fabricio Silva Southern Northeast Brazil (SNE) Stations

22. FMA Regional Atmospheric and Oceanic Features The patterns of anomalous outgoing longwave radiation (OLR) over Northeast Brazil and northern South America are similar for both years (see next slide, top panels). SST anomalies in the eastern equatorial Pacific (next slide, middle panels) are quite different in the two years (positive in 2012 and near zero in 2013), SST anomalies in the subtropical and equatorial Atlantic were negative in 2012 and positive in 2013. The divergent circulation (next slide, bottom panels) shows anomalous mid-level (~500 hPa) rising motion (upper-level divergence and low-level convergence) over the western Amazon basin and sinking motion (upper-level convergence and low-level divergence) over NE Brazil in both years.

23. . Anomalous OLR, SST and Divergent Circulation

24. Summary The rainy season onset phase (SON) featured rainfall deficits of 200-400 mm or more over parts of the Amazon basin, central and southern Brazil. Above- average rainfall was observed over central Colombia, portions of Peru, Paraguay and eastern Argentina. ENSO-neutral conditions were present in the tropical Pacific. During the mature phase of the monsoon (DJF) rainfall was below average over central, Northeast and most of Southeast Brazil, eastern Bolivia and northern Argentina, with rainfall deficits greater than 300 mm in many areas. Above- average rainfall was observed over portions of Colombia, northwestern Brazil, Peru, Uruguay and extreme southern Brazil. ENSO-neutral conditions continued in the tropical Pacific. During the decay phase of the rainy season (MAM), rainfall was below average over western, northeastern and southern Brazil, Venezuela, and northern Argentina, with deficits greater than 300 mm observed over portions of those regions. Above-average rainfall was observed over central Colombia, Paraguay and portions of the central Amazon basin in Brazil. SST’s were near average throughout most of the equatorial Pacific. In general, rainfall deficits were observed over most of South America during September 2012-May 2013, with the core monsoon region (Brazilian Plateau) experiencing the largest deficit in the historical record (1979-2013).