The east coast of South America is under the influence of cold ocean currents, while the west coast is under the influence of warm ocean currents.
The ocean current that is dominant along side the east coast of South America is the South Pacific ocean current, which is a cold current, resulting in low precipitation and dry conditions along side the east coast.
The ocean current that is dominant along side the west coast is the Brazil ocean current, an extension of the South Equatorial ocean current, which is warm current, resulting in high precipitation and very warm and humid conditions along side the west coast.
