Oilseeds newsletter Oil World said it had cut its forecast of Brazil's soyabean harvest this season to 50.2 million tonnes, down from last season's crop of 52.0 million tonnes.
In late April, Oil World had estimated the crop at 51.0 million tonnes. In March, before weather damage cut yields, it had forecast a huge 54-55 million tonne crop.
Brazil is one of the world's leading soyabean exporters and is key to meeting global demand.
"We have now reduced our production estimate to 50.2 million tonnes in response to the lower-than-expected yields achieved in Rio Grande do Sul," it said.