Meteorologist David Tolleris of WxRisk.com says a similar weather pattern has developed across South America as seen a year-ago. The reason: La Nina.
"If you recall last December 2010, January 2011 and February 2011 there was a high-end moderate strength La Nina underway," he notes. "And this year -- here in December 2011 -- we once again have a moderate La Nina event underway. The La Nina pattern in South America is pretty basic but it is also quite dominant when it shows up. Assuming the La Nina event is either of moderate or strong intensity... the weather pattern features one with excessive rainfall over much of central and east central Brazil (Minas Gerais, Sao Paulo and Goias and to a lesser degree Mato Grosso), while Paraguay, southwest and southeastern Brazil and most of Argentina is dry. Sometimes these areas are VERY dry."
Look forward to January, Tolleris says to expect more of the same. "In a general sense the pattern is probably going to resemble what we sought in January 2011 -- wet and at times excessively wet conditions over central and east central Brazil and fairly dry if not very dry over southeast Brazil, Paraguay and most of central and eastern Argentina."