Typically, the wet season in Brazil starts around Sept. 26 on average. That is according to USDA Chief Meteorologist Mark Brusberg, who found that is the date the state of Mato Grosso typically sees its first 30 millimeters (1.2 inches) of rainfall.
But we are getting way past the normal timeline for the start of the wet season with continued dryness in the forecast. The developing La Nina is likely to blame. La Nina is the term given when Pacific Ocean equatorial temperatures reach a sustained value of at least 0.5 degree Celsius below average. Brusberg has found that La Nina tends to push back the beginning of the wet season sometimes well into October.
That is unfortunate for area farmers waiting to plant corn and soybeans. After months of heat and dryness, both topsoil and subsoil moisture are at a minimum and rainfall will be needed to promote good seed-to-soil contact, not to mention germination.
The forecast continues to suggest a very late start to the season. The European model has little to no rainfall in its forecast for Mato Grosso and the surrounding areas through Oct. 9, at least a two-week delay to the start of the season. Longer-range models start to promote showers after that date, getting to the 30 mm threshold on Oct. 13-14. A start this late would not affect the current season's crop as much as it would the second, safrinha crop.
Brazil, and Mato Grosso in particular, counts on a tight planting window in the spring to ensure that the second crop of corn or cotton can get in the ground with enough time to enjoy the wet season rains into reproduction stages. If the wet season wanes like it typically does, though, La Nina may mean an earlier end to the wet season as well -- a two-week planting delay this spring could start the dry season in an unfavorable time in the corn or cotton's development cycle.
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 Brusberg during the 2018 Agricultural Outlook Forum Grain and Oilseeds Session on Feb. 23, 2018.
A link can be found here: https://www.usda.gov/…
John Baranick can be reached at firstname.lastname@example.org
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