The International Coffee Organization flagged the headwind to Brazilian coffee exports from a firmer real, as well as weakened inventories, even as industry data showed a slow post-harvest pick-up in volumes.
The ICO - while flagging that global coffee exports had "remained at a very high level" into July, rising 11% year on year to 9.4m bags - contrasted the strong global performance with a decline in shipments from Brazil.
Volumes from Brazil, the top coffee growing and exporting country, dropped 11% to 1.75m bags, including soluble coffee, "the lowest since February 2004, " the organisation said.
The downturn reflected in part weak exportable supplies, depleted by "the previously poor harvest", when robusta coffee output in particular was hurt by drought.
The ICO also flagged an "unfavourable dollar exchange rate eroding the competitiveness of Brazilian coffee on the world market".
Indeed, the real has recovered by 7.1% against the dollar so far in 2017, so making Brazilian exports less affordable to buyers in dollars, the currency of international trade in many commodities, including coffee.
By contrast, the ICO underlined "significant increases in" coffee exports from Colombia, the second-biggest grower and shipper of arabica coffee beans, and whose currency, the peso, has held steady against the dollar so far this year.
Colombian "volumes shipped during the month of July have doubled compared to last year", the organization said, if acknowledging that the year-before figure was unusually depressed thanks to a truckers' strike.
"Nonetheless, the recent figures represent a continuation of this coffee year's strong export performance," with Colombia's shipments for 2016-17, which started in October, up 11.6% year on year as 11.2m bags.
The comments came even as Cecafe, the Brazilian coffee exporters' industry group, unveiled data for last month showing total exports of 2.37m bags.
The data represented a marked pick-up from July, and a reflection of the boost to exportable supplies from the arabica coffee harvest.
"August brings a better outlook for exports," said Nelson Carvalhaes, the Cecafe president, flagging "signs of recovery".
However, with the performance representing the weakest for any August since at least 2009, Mr Carvalhaes urged caution over revival prospects nonetheless.
While this month "should again see higher volumes, around 20% higher" than in August, even an increase at that level, implying September shipments of some 2.85m tonnes, would represent a decline in volumes of 7% year on year, on Cecafe data.
The boost to Brazil's coffee exports from the 2017 crop has been delayed in part by wet weather which, besides slowing the harvest, has hampered the drying of beans too, to render them fit for storage.
Furthermore, there has been talk of Brazilian growers holding off sales in the hope of higher prices.
In fact, Brazilian arabica prices are, at R$444.12 a bag according to research institute Cepea, down some 8.6% so far in 2017, with those of robusta beans down 19.8% at R$395.58 a bag, weighed by improved production after rain relief to drought-hit growing areas.
By Mike Verdin