The soil was already unusually dry from just north of Tauranga through to Whakatane and the Waikato.
El Nino conditions usually included high winds which further dried out the land, he said.
"For November, December and January we think in terms of temperature it will be average or below average for the east and north of the island. That doesn't mean there won't be warm days or warm weeks."
On average it was expected rainfall would be below normal for the next three months.
It may be good news for holidaymakers but could hit farmers hard. Federated Farmers Bay of Plenty president Rick Powdrell said October had been a noticeably dry month.
He recorded 30mm of rain on his Rangiuru Rd farm last month compared to 62.5mm in October 2014, 52mm the year before and 108.5mm in October 2012.
"We did have a very wet September, so that's probably helped to a degree," he said. "We're certainly in all right condition.
"Most people seem to have okay amounts of grass. Some of the dairy farmers have been making some silage."
November was typically a dry month but December had been fairly wet in recent years, Mr Powdrell said.
"It's the next couple of months that's critical."
Windy conditions had further dried out the land, he said.
"In the past when we've had really trying conditions it's usually been wind driven," he said.
Often El Nino conditions brought a variety of weather to the region with farms on the coast doing it toughest while those more inland benefited from rain in the hills, Mr Powdrell said.
He encouraged farmers to think about where there was flexibility in their business.
For some that might mean making provisions to buy extra feed while for others it might mean reducing their stock levels earlier than they had planned, he said.
The Dairy NZ economics group said it predicted milk production in the Bay of Plenty to be down about 6 per cent for the season and the El Nino weather system could have dire effects over summer.
Dairy NZ senior economist Matthew Newman said the magnitude of lower milk would depend on the severity of the dry summer.