"There are so many variables that go into the forecast - it is quite a difficult algorithm. It could be any one or a combination of things."
Harvest ends in about two weeks, with later varieties including Braeburn most affected.
Wet weather delayed harvest but he did not consider a factor. The current season enjoyed "a great growing season delivering fruit with some of the best eating qualities ever".
Overseas markets have been advised of the lower forecast.
"It is likely that in some of our key markets, such as Europe and the UK, volumes will be at or below those achieved last season."
He said exports were currently at their peak and flowing smooth through Napier Port.
The port has never been busier, with cargo diverted from Wellington's earthquake-damaged CentrePort. Extra shifts and staff have been employed to handle the windfall volume.
"We were a bit worried about the impact of Wellington freight but Napier Port have done a good job," Mr Pollard said.
Mr Pollard said despite the lower crop estimate he remained confident the New Zealand apple and pear industry would achieve $1 billion in export revenue before the 2022 target. In 2016 export revenue was $720 million.
The projected volume of apple exports in 2022 will require more than 10,000 20ft containers than were used last season.