Spring-like weather has peppered the country with wind and showers every few days for the past few months.
"For the final two months of 2013 we've seen very little in the way of big, settled highs.
"This was great for farmers who desperately needed rain, but now holidaymakers desperately want the sun."
Signs of summer were now finally on their way, he said.
"We see a monster of a high pressure system south of Australia in the first half of January and we expect this giant anticyclone to slowly drift towards New Zealand by the end of week two," Mr Duncan said.
While the weather would settle down with the high, it wouldn't be summer in New Zealand without the threat of a tropical storm, Mr Duncan said.
Long-range forecasts showed a tropical storm that could drift towards New Zealand in the second week of January.
However, the incoming high from Australia could push it back out into the Pacific Ocean, WeatherWatch predicted.
MetService meteorologist Daniel Corbett said the weather in the first week of January would be "fast and furious" across the country.
"The raincoat is going to get a bit of use unfortunately ... until we get a decent high."
January temperatures would average in the low- to mid-20s in most places, he said.
January weather
* Hottest: Eastern areas like Hawkes Bay and Marlborough will enjoy the highest temperatures this month.
* Wettest: The West Coast of the South Island can expect persistent rain or showers for the first 10 days of the year, clearing later in the month.
* Driest: Northland, eastern Coromandel and Bay of Plenty will be the driest spots.
* Windiest: Wellington will be the windiest place to be, but breezes will settle down mid-January.
Source: WeatherWatch.