The South American Monsoon System:

Recent Evolution and Current Status

Update prepared byClimate Prediction Center / NCEP

26 November 2007

Outline

• Recent Evolution and Current Conditions

• Summary

• Climatology

Rainfall Patterns: Last 30 Days

Below-normal rainfall has been observed over most of Brazil, except for the western Amazon Basin and the southern portion of the country. Below-normal rainfall was also observed over Uruguay and northern Argentina.

Rainfall Patterns: Last 90 Days

Below-normal rainfall has been observed over most of Brazil, with rainfall deficits of more than 175 mm in central Brazil. Slightly above-normal rainfall was observed ove eastern Bolivia, Paraguay and extreme southern Brazil.

Recent Evolution: Rainfall

• The SAMS wet season was delayed in many areas.

• Recently, seasonal-to-date rainfall has increased to near normal in western Brazil, but rainfall deficits continue over the Brazilian Plateau (BP), with deficits around 150 mm during the last 3 months.

BP

Recent Evolution: OLR

• During 23 October-1 November (top panel) enhanced precipitation (negative OLR anomalies) was observed over portions of southeastern and southern Brazil. Positive OLR anomalies (drier-than-average conditions) covered most of the Amazon Basin, Northeast Brazil, and central Argentina.

• During 2-11 November, wetter-than normal conditions strengthened over southeastern Brazil, while drier-than-normal conditions continued over Northeast Brazil.

• During 12-21 November drier-than-normal conditions dominated central and Northeast Brazil, while slightly wetter-than-normal conditions were observed over Southeast Brazil.

Atmospheric Circulation & OLR

Last 5 days

• During the last 5 days low OLR (left panel) was observed from the western Amazon southeastward across southeastern Brazil and over the western South Atlantic Ocean.

• However, precipitation was generally below normal (positive OLR anomalies, right panel) over all of Brazil and most of Argentina.

• During this period an amplified 200-hPa ridge was located over northern Argentina and southern Brazil.

Summary

• Season-to-date rainfall has been near normal in western Brazil.

• The rainy season has been slow to start over central and southeastern Brazil.

• During the last 90 days, rainfall deficits of ~150 mm have been observed over portions of central and southeastern Brazil.

ClimatologyClimatology

Rainy Season DatesRainy Season DatesONSETONSET DEMISEDEMISE

Precipitation Climatology Precipitation Climatology