Adverse weather from April through to mid-July and an early flowering hampered the main crop, which will be harvested from October 2020 to March 2021 and will likely bring in some 1.63 million tonnes of cocoa versus 1.69 million in 2019/20.
This is according to average forecasts from four leading traders and experts with cocoa pod counters on the ground.
"The crop didn't start well but it's improving now," said an Abidjan-based trader at one the world's largest cocoa suppliers.
Participants in an early August Reuters poll said output in Ivory Coast, which grows roughly 40% of the world's cocoa, would rise to 2.24 million tonnes in 2020/21 from 2.15 million in 2019/20.
They did not break down the number into main and mid-crop, though the main crop usually accounts for three-quarters of the total.
Cocoa prices hit 1-1/2 year lows in mid-July on signs the coronavirus pandemic had slashed global demand for the chocolate ingredient, and bets cocoa output would rise in 2020/21, leaving the market with a large surplus.
Prices have since recovered to trade near their highest since March on talk demand had rebounded somewhat and fears supplies might be disrupted if unrest escalates in Ivory Coast ahead of the November presidential elections.
A smaller Ivorian crop that leaves the global market with 60,000 tonnes less cocoa than expected could boost prices, reducing by about a quarter the 220,000-tonne surplus forecast in Reuters' August poll.
"The Ivory Coast (main) crop development underperformed. Versus (previous market surplus) estimates, it's bullish," said a London-based industry expert.
In world No. 2 cocoa producer Ghana, which produces some 20% of global output, the 2020/21 main crop will likely be little changed year-on-year at around 680,000 tonnes, three of the traders said.
By Maytaal Angel and Ange Aboa