The country could be hit by its first major tropical storm of the season in the second week of the new year.
WeatherWatch said the changeable spring-like weather would likely continue into the first half of the month.
It comes as parts of the North Island experience a drier than average start to summer with no prospect of significant rain in the next seven days.
However, the weather in the tropics around northeastern Australia and the tropical islands north of New Zealand was heating up and storms and downpours are increasing.
Some long-range models were showing a potential ex-Australian low rapidly deepening over New Zealand and bringing a storm to the country in the second week of January.