South America Calling

Wet Season Starts Thursday in Central Brazil, Some Questions Still Remain

John Baranick
By  John Baranick , DTN Meteorologist
Models bring rain into central Brazil, circled, but do so at different intensity and coverage. The European model on the left is much more aggressive than the American GFS model on the right. (DTN graphics)

It is finally here, the true start to the wet season rainfall in central Brazil. Producers have been waiting for a long time for rain to start coming. Typically, these showers start up in September, the first 30 millimeters (1.2 inches) accumulates by the end of the month, and daily showers increase throughout October. That has not been the case this year. Any showers that occurred in September and early October have been very spotty and for most areas, very light. DTN estimates that less than 10 mm have fallen in the states of Minas Gerais, Goias, and eastern Mato Grosso, while only small areas of central and western Mato Grosso, Mato Grosso do Sul, and Sao Paulo have recorded more than that. These areas account for roughly half of corn and soybean production for the country and rely on a good start to the wet season to plant their soybeans.

Producers harvest soybeans in late January and February and plant their second-season (safrinha) corn immediately after. If they can do so in a timely manner, then they can get the vast majority of the corn through pollination before the wet season rains shut down in late April or early May. The delays to the wet season have forced producers to delay planting their soybean crop. The delay usually has a minimal effect on their soybean production but exposes more of their safrinha corn to the dry season, which could have large effects. We saw a similar situation occur in the 2020-21 season.

The situation finally changed on Oct. 10 as a system moved up from southern Brazil and started to spread more rainfall throughout the region. It will be interesting to see if producers can make up for lost time on their soybean planting, or if a large portion will be delayed. The portion of the crop still to be planted at the beginning of November will give us an indication on how exposed the safrinha corn crop will be.

And it's not all certain how that will unfold. Producers generally have large operations and can only cover so much ground at a time. With only three weeks left in the month, it may be difficult to press on hard enough to get all the acres planted. And the weather still has to cooperate.

Although the wet season rains have truly begun, models differ on the amount and coverage of rainfall that will occur. The front that is bringing the showers will largely dissolve on Oct. 12. However, both the American GFS and European ECMWF model both show rain continuing afterward, through next week.

What they don't agree on is the coverage or intensity of the showers. Even with the current system, the ECMWF is much more aggressive about producing widespread heavier showers than the GFS, which is much more subdued on both ends. The showers that continue next week are generally similar. The ECMWF produces widespread amounts of 50-100 mm (about 2-4 inches) across the entirety of central Brazil through Oct. 19 with pockets of heavier rainfall over Goias. Meanwhile, the GFS at the same time is producing much spottier areas of more than 30 mm in Mato Grosso, and some areas being left out with less than 10 mm (0.4 inches). The GFS maintains the focus of rainfall in the 50- to 100-mm range farther east in Minas Gerais, leaving most of the region in the 25- to 50-mm (about 1- to 2-inch) range.

At first glance, this may seem to be a major discrepancy and issue. If the GFS is closer to being correct, that would mean a lot less rainfall for areas in drought in Mato Grosso, Goias, and Mato Grosso do Sul. That is true, but it may not matter. With rainfall starting, producers are likely to plant regardless of whether the rain is heavy or if it is spotty and scattered. Soybeans do not need much rainfall in their early life cycle, they require more if it's later and especially during pod-fill, which occurs in December and January and is usually very consistent regardless of how the season starts. There may be some instances of soybeans getting dry and burning up, but the likelihood of that affecting the final production in the country is low.

To find more international weather conditions and your local forecast from DTN, visit https://www.dtnpf.com/….

John Baranick can be reached at john.baranick@dtn.com

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