South America Calling

Late Start Likely to Brazil Rainy Season

Bryce Anderson
By  Bryce Anderson , DTN Senior Ag Meteorologist
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Bright red over most of Brazil means short to very short soil moisture, including the top production state of Mato Grosso. (PECAD FAS graphic)

The onset of the rainy season in most of Brazil is still delayed. A few showers are indicated in the forecast through Tuesday, Sept. 22, but occurrences are likely to be scattered in coverage with uneven amounts. This is not a general soaking pattern for most soybean areas. The Sept. 15 USDA Weekly Crop Weather Bulletin notes that "... for many farming areas, it was the third consecutive week of drier-than-normal weather."

A possible factor in the delayed start to the Brazil wet season is the presence of La Nina in the Pacific Ocean. La Nina -- the development of sustained equatorial Pacific temperatures at least 0.5 degree Celsius below normal -- has a strong relation to a late start to the Brazil rainy season.

Tracking the beginning of the rainy season in Brazil's largest soybean producing state of Mato Grosso, USDA Chief Meteorologist Mark Brusberg found that La Nina episodes from 2000 to 2017 generally led to a later-than-average beginning of the wet season. Brusberg found that the average starting date for Mato Grosso to receive at least 30 millimeters rain (1.2 inches) was Sept. 26.

In this timespan, Brusberg identified eight years when La Nina was in effect: 2000, 2005, 2007, 2008, 2010, 2011, 2016 and 2017. In these years, the Mato Grosso rainy season began earlier than the Sept. 26 average on three occasions -- 2000 (Sept. 14), 2005 (Sept. 24) and 2016 (Sept. 28). He also identified five years of the eight La Nina years when the rainy season began later than the Sept. 26 average date: 2007 (Oct. 15), 2008 (Oct. 3), 2010 (Oct. 3), 2011 (Oct. 5) and 2017 (Oct. 22).

The lack of significant rain in the Brazil forecast suggests that 2020 will join the five "late start" years in having the Mato Grosso rainy season begin late -- after the Sept. 26 average starting date.

Details on the average Mato Grosso rainy season starting date are from a report titled "La Nina and Its Impact on South American Agriculture" presented by Mark Brusberg, chief meteorologist, USDA and World Agricultural Outlook Board, during the 2018 Agricultural Outlook Forum Grain and Oilseeds Session Feb. 23, 2018.

Bryce Anderson

Twitter: @BAndersonDTN

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