Those most at risk of showers on Christmas Day are the North Island ranges, the west coast of the South Island and pockets of Northland.
Those areas would be "caught up in a humid easterly or northeasterly wind flow," Duncan said.
In the main centres, Auckland and Tauranga could get a drop of rain but Hamilton, Wellington, Dunedin and Christchurch should be dry. Christchurch was looking hot as a norwester was likely to push temperatures to the upper 20s.
"Some of the northern areas will be a bit gloomy but nowhere will be wintry."
Metservice forecaster Andy Downs also picked a dry Christmas for most of the country. Pesky showers would only make their presence felt north of Orewa, in parts of Northland and south of the glaciers in the South Island.
Duncan said a touch of El Nino had prolonged spring, but he wasn't surprised by the weather during what was traditionally considered the first month of summer.
"It's gradually getting better. We've had bursts of wet weather from Australia. The long-range trend shows more high pressure so we will shift to more highs and fewer rainmakers."
It was too early to say what the weather would be like for New Year's revellers, but a low arriving after Christmas could bring rain to the west of the South Island and make it hotter and drier in the east.
"We have to remember we're two mountainous islands, we're in the Roaring Forties, we're on the edge of the Southern Ocean and the edge of the subtropics and we've got the Australian desert just a couple of hours' flight away," Duncan said.
"Those factors make it hard to pinpoint weather long range."
