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The South American Monsoon System Summary September 2014-May 2015

The South American Monsoon System Summary September 2014-May 2015. Prepared by Vernon E. Kousky Climate Prediction Center / NCEP June 2015. For more information, visit: http://www.cpc.ncep.noaa.gov/products/Global_Monsoons/American_Monsoons. Summary : Onset Phase.

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The South American Monsoon System Summary September 2014-May 2015

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  1. The South American Monsoon System SummarySeptember 2014-May 2015 Prepared by Vernon E. Kousky Climate Prediction Center / NCEP June 2015 For more information, visit:http://www.cpc.ncep.noaa.gov/products/Global_Monsoons/American_Monsoons

  2. Summary : Onset Phase • The rainy season onset phase (SON) featured: • Below-average rainfall over most of Venezuela, the Amazon Basin, central and southeastern Brazil, with rainfall deficits exceeding 300 mm in parts of Venezuela and west-central Brazil. • Above-average rainfall was observed over central Colombia, portions of Peru, Uruguay and eastern Argentina. • Borderline weak El Niño conditions were present in the tropical Pacific.

  3. Summary : Mature Phase • The rainy season mature phase (DJF) featured: • Below average rainfall over the central and eastern Amazon Basin, and central and Southeast Brazil, with rainfall deficits greater than 400 mm in several areas. • Above-average rainfall was observed over southern Colombia, northern Peru, northwestern Bolivia, Uruguay and portions of north-central Argentina. • Weak El Niño conditions were present in the tropical Pacific.

  4. Summary : Decay Phase • The rainy season decay phase (MAM) featured: • Below-average rainfall over Venezuela, the central and eastern Amazon Basin, northern Northeast Brazil, southern Brazil, Uruguay and northeastern Argentina, with deficits greater than 400 mm observed over portions of Venezuela and the Amazon Basin. • Above-average rainfall was observed over southern Colombia, northern Peru and Paraguay. • Strengthening El Niño conditions were present in the tropical Pacific.

  5. General Summary • In general, below-average rainfall was observed over most of Brazil and Venezuela during September 2014-May 2015, with less than 50% of average precipitation in several areas. Above average rainfall occurred over northern Peru, southern Paraguay, and portions of Argentina. • Northern Northeast Brazil experienced its fourth consecutive year of drought conditions. • Southeast Brazil experienced its driest September-May rainy season since the mid-1950s.

  6. Outline • Onset phase • Mature phase • Decay phase • Seasonal Departures from Average • Northeast Brazil drought • Southeast Brazil drought • Summary

  7. SAMS Core Region SAMS core region (Central Brazil – CBR)

  8. Precipitation Climatology ONSET DATES

  9. Precipitation Departures: Onset Phase (Sep-Nov 2014) During September-November 2014 rainfall was below average over most of Venezuela, the Amazon Basin, central and southeastern Brazil, with rainfall deficits exceeding 300 mm in parts of Venezuela and west-central Brazil. Above-average rainfall was observed over central Colombia, portions of Peru, Uruguay and eastern Argentina.

  10. SON Historical Time Series for CBR Region 1981-2010 mean 2014

  11. SON Historical Time Series for CBR Region • 11 of the last 13 years have featured below-average precipitation over the CBR region during the onset phase of the SAMS wet season. • During SON 2014 total rainfall was the second lowest during the period of record (1979-2014). Rainfall during SON 2014 was about 65% of average (deficit ~140 mm).

  12. Tropical Pacific and Atlantic SST Anomalies (Sep-Nov 2014) During September–November 2014, SSTs were above average throughout the equatorial Pacific Ocean (180°W-80°W) (borderline weak El Niño conditions). In the tropical Atlantic, SSTs were slightly above average from northern South America to the West coast of North Africa and near average along and south of the Equator.

  13. Precipitation Departures: Mature Phase (Dec 2014-Feb 2015) During December 2014-February 2015 rainfall was below average over the central and eastern Amazon Basin, and central and Southeast Brazil, with rainfall deficits greater than 400 mm in several areas. Above-average rainfall was observed over southern Colombia, northern Peru, northwestern Bolivia, Uruguay and portions of north-central Argentina.

  14. DJF Historical Time Series for CBR Region 1981-2010 mean

  15. DJF Historical Time Series for CBR Region • The last 11 years have featured near- or below-average precipitation over the CBR region during the mature phase of the SAMS wet season. • The lowest total in the period of record occurred in DJF 2014/15. Rainfall was about 65% of average (deficit ~290 mm).

  16. Tropical Pacific and Atlantic SST Anomalies (Dec 2014-Feb 2015) During December 2014–February 2015, positive SST anomalies were observed throughout most of the equatorial Pacific (weak El Niño conditions). Over the Atlantic, equatorial SSTs were near or slightly below average.

  17. Precipitation Climatology END DATES

  18. Precipitation Departures: Decay Phase (Mar-May 2015) During March-May 2015 rainfall was below average over Venezuela, the central and eastern Amazon Basin, northern Northeast Brazil, southern Brazil, Uruguay and northeastern Argentina, with deficits greater than 400 mm observed over portions of Venezuela and the Amazon Basin. Above-average rainfall was observed over southern Colombia, northern Peru and Paraguay.

  19. MAM Historical Time Series for CBR Region 1981-2010 mean

  20. MAM Historical Time Series for CBR Region • During the last 18 years (1998-present) rainfall has been near or below average over the CBR region during the decay phase of the SAMS wet season. • During MAM 2015, rainfall was about 90% of average (deficit ~40 mm).

  21. Tropical Pacific and Atlantic SST Anomalies (Mar-May 2015) During March-May 2015, equatorial SSTs were above average in the Pacific Ocean (strengthening El Niño conditions). In the tropical Atlantic, SSTs were above average south of the equator and below average north of the equator.

  22. Precipitation Departures: September 2014- May 2015 During September 2014 - May 2015 rainfall was below average throughout most of Brazil and Venezuela (percent of average less than 50% in several areas), and above average over northern Peru, southern Paraguay, and portions of Argentina.

  23. SONDJFMAM Historical Time Series for CBR Region 1981-2010 mean

  24. SONDJFMAM Historical Time Series for CBR Region • There has been a noticeable downward trend in precipitation over the CBR region during the SAMS wet season, especially since 2005. • Since 2005 the gridded precipitation analyses have used only real-time station observations. • The number of real-time stations is considerably less than the number of historical stations available in making the gridded analyses for the period 1979-2005, especially in the CBR region. • Thus, the magnitude of the decrease is in doubt.

  25. Northeast Brazil Drought • During February-April 2015 rainfall was between 70% and 80% of the average in northern NE Brazil and near average in southern Northeast Brazil. • Northern NE Brazil experienced its fourth consecutive drier than average February-May (see next slide).

  26. February-April Historical Time Series 1981-2010 mean 1981-2010 mean In NNE and SNE FMA 2012-2015 (red box) rank as the driest four consecutive FMA periods during 1979-2014.

  27. Southeast Brazil Drought • For the second consecutive rainy season, exceptionally dry conditions dominated Southeast Brazil, especially during the peak of the wet season (December-February). • Rainfall during DJF 2014-15 was only 50% of the average in many areas within the region. • The following slides give a historical perspective to the drought conditions in Southeast Brazil during the peak of the rainy season (December-February) and the entire rainy season (September-May).

  28. Southeast Brazil Drought The region over Southeast Brazil (SEBR) selected for analysis is shown in this figure.

  29. Southeast Brazil Drought (DJF) DJF 2014/15 was the driest DJF season during the period of record for the OI-based analyses (1979/80 – present).

  30. Southeast Brazil Drought: September-May OI analysis 1979-present (green line) Cressman analysis (Brazil data only) 1948-2005 (black line) September 2014-May 2015 was the driest rainy season since 1954-1955. (Note: the Cressman analysis and the OI agree quite well during the period of overlap, 1979-2005.)

  31. Summary : Onset Phase • The rainy season onset phase (SON) featured: • Below-average rainfall over most of Venezuela, the Amazon Basin, central and southeastern Brazil, with rainfall deficits exceeding 300 mm in parts of Venezuela and west-central Brazil. • Above-average rainfall was observed over central Colombia, portions of Peru, Uruguay and eastern Argentina. • Borderline weak El Niño conditions were present in the tropical Pacific.

  32. Summary : Mature Phase • The rainy season mature phase (DJF) featured: • Below average rainfall over the central and eastern Amazon Basin, and central and Southeast Brazil, with rainfall deficits greater than 400 mm in several areas. • Above-average rainfall was observed over southern Colombia, northern Peru, northwestern Bolivia, Uruguay and portions of north-central Argentina. • Weak El Niño conditions were present in the tropical Pacific.

  33. Summary : Decay Phase • The rainy season decay phase (MAM) featured: • Below-average rainfall over Venezuela, the central and eastern Amazon Basin, northern Northeast Brazil, southern Brazil, Uruguay and northeastern Argentina, with deficits greater than 400 mm observed over portions of Venezuela and the Amazon Basin. • Above-average rainfall was observed over southern Colombia, northern Peru and Paraguay. • Strengthening El Niño conditions were present in the tropical Pacific.

  34. General Summary • In general, below-average rainfall was observed over most of Brazil and Venezuela during September 2014-May 2015, with less than 50% of average precipitation in several areas. Above average rainfall occurred over northern Peru, southern Paraguay, and portions of Argentina. • Northern Northeast Brazil experienced its fourth consecutive year of drought conditions. • Southeast Brazil experienced its driest September-May rainy season since the mid-1950s.

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