The South American Monsoon System Summary

July 2007-June 2008

Update prepared byClimate Prediction Center / NCEP

June 2008

For more information, visit:

http://www.cpc.ncep.noaa.gov/products/Global_Monsoons/American_Monsoons

Outline

• Onset phase

• Mature phase

• Decay phase

• Long-Term Departures from Average

• Summary

Precipitation Climatology

ONSET DATESONSET DATES

Precipitation Departures: Onset Phase (Sep-Nov 2007)

During the 90-day period (1 September-30 November 2007) rainfall was below normal over most of Brazil, with rainfall deficits exceeding 175 mm in portions of the southern Amazon, and central and southeastern Brazil (red oval). Above-normal rainfall was observed over southern Colombia, northern Peru, Ecuador, eastern Bolivia, most of Paraguay and portions of southern Brazil and Uruguay.

Mean and Anomalous 200-hPa Winds and 500-hPa Vertical Motion

• An anomalous cyclonic circulation center was located near the central coast of Chile and an anomalous anticyclonic circulation center was located over the western Atlantic.

• Enhanced upward vertical motion (negative omega) extended from southern Colombia south-southeastward over western Brazil, eastern Bolivia, Paraguay, northeastern Argentina and southern Brazil. Anomalous downward vertical motion (positive omega) covered central Chile and most of central and eastern Brazil.

C A

Precipitation Departures: Mature Phase (Dec 07-Feb 08)

During the 90-day period (1 December 2007-29 February 2008) rainfall was below normal over most of Brazil south of the equator, with rainfall deficits greater than 250 mm in portions of central and southeastern Brazil (red oval in right panel). Above-normal rainfall was observed over southern Colombia, Peru, Ecuador, Bolivia, Paraguay, northern Chile and northwestern Argentina.

Mean and Anomalous 200-hPa Winds and 500-hPa Vertical Motion

• An anomalous anticyclonic circulation center was located near the northern coast of Chile. This represents a southwestward shift in the mean position of the Bolivian Anticyclone, which is typically found over western Brazil and eastern Bolivia in Summer.

• Enhanced upward vertical motion (negative omega) extended from southern Colombia south-southeastward over western Brazil, eastern Bolivia, Paraguay, northeastern Argentina and southern Brazil. Anomalous downward vertical motion (positive omega) covered central Chile and northeastern Brazil.

A

Precipitation Climatology

END DATESEND DATES

Precipitation Departures: Decay Phase (Mar-May 08)

During the 90-day period (1 March-31 May 2008) rainfall was below normal over the southern Amazon, southern Brazil, Uruguay and eastern Argentina. Above-normal rainfall was observed over southern Colombia, Ecuador, Peru, the eastern Amazon and northeastern Brazil.

Mean and Anomalous 200-hPa Winds and 500-hPa Vertical Motion

• Anomalous anticyclonic circulation covered the low-latitudes of the western Atlantic. An anomalous trough was located over southern Brazil and northeastern Argentina.

• Enhanced upward vertical motion (negative omega) covered northwestern South America, extending southeastward to portions of southern Brazil. Anomalous downward vertical motion (positive omega) covered central Chile, eastern Argentina and Uruguay.

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Precipitation Departures: July 2007-June 2008

During the period 1 July 2007-22 June 2008 rainfall was below normal the southern Amazon, portions of southeastern and southern Brazil, portions of Uruguay and eastern Argentina. Above-normal rainfall was observed over southern Colombia, Ecuador, most of Peru, the eastern Amazon and northeastern Brazil.

NOTE: There is a lack of data for Colombia and Venezuela, so the deficit in rainfall over those regions is not real.

Precipitation Anomaly Patterns during La Niña Episodes over Brazil

From Silva et al., 2007

2007-2008

The pattern of anomalous precipitation over Brazil for the water year (July 2007-June 2008, figure above) is consistent with the La-Nina composite.

Summary• The rainy season onset was delayed over the southern Amazon,

central and southeastern Brazil. This resulted in large rainfall deficits (greater than 250 mm) in some areas during September-November 2007. Rainfall was above average over southern Colombia, Ecuador and northern Peru.

• Rainfall was below average in central and southeastern Brazil during December 2007-February 2008, with deficits greater than 250 mm in some areas. Rainfall was above average over the northern Amazon, southern Colombia, Ecuador, Peru, Bolivia, northern Chile and northwestern Argentina.

• Rainfall was above average over central and northeastern Brazil during March-May 2008, with surpluses exceeding 250 mm in many areas. Rainfall was also above average over southern Colombia, Ecuador and Peru. Rainfall was below average over southern Brazil, eastern Argentina and Uruguay.

• The pattern of rainfall departures for the water year (July 2007-June 2008) is similar to the composite for La Niña episodes.