Further south in Wellington, the weather was more tricky to predict, Mr Miller said.
"We are looking at cloudy periods and a few showers, they should clear off during the day."
The forecast would become more reliable as Christmas drew nearer, Mr Miller said.
"With the nature of weather forecasting, the closer you get the more confident you can be in your forecast."
WeatherWatch forecaster Philip Duncan was predicting warm weather for most on Christmas Day, thanks to a large high pressure system to the east of the country.
"It's going to mean light winds across most of the North Island and a developing north westerly across the South Island."
He said northwesterlies were likely to bring showers to the South Island's West Coast, and a few showers could pop up elsewhere into the afternoon.
"We still think the majority of the main centres look dry, if not for most of the day, for Christmas."
Mr Duncan has picked Canterbury as this year's Christmas hot spot.
"Canterbury looks like it could be one of the hotter places... we think that Christchurch on Thursday could be going up to 26C, so that's nice and hot."
Typical Christmas holiday spots such as the Bay of Islands, Coromandel and Gisborne would experience less settled weather thanks to an easterly flow, Mr Duncan said.
The coolest spot to celebrate Christmas is likely to be New Zealand's Scott Base in Antarctica, which would enjoy a high of -6C on and a low of -9C.
"The forecast is looking pretty good ... it's not exactly the warmest day of the week ... but the weather is looking mostly clear," Mr Duncan said.
"It will be perfect for Santa."
Closer to the mainland, the weather was looking great for the Chatham Islands, which would have the high pressure system directly above them on Christmas Day.
Islanders were likely to get mostly fine spells, a few clouds and a high of 20C.
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Christmas Day:
Whangarei - Cloudy periods with a few showers. Easterlies. High 22C Low 15C
Auckland - Cloudy periods. Easterly breezes. High 21C Low 15C
Hamilton - Fine spells. Northeast breezes. High 22C Low 10C
Tauranga - Cloudy periods. Northeasterlies. High 21C Low 15C
Wellington - Cloudy periods, few showers until evening. Northwesterly develops. High 20C Low 15C
(Source: MetService)
*
Boxing Day:
Whangarei - Cloudy with northeasterlies. High 22C Low 15C
Auckland - Cloudy. Northeasterlies. High 20C Low 14C
Hamilton - Partly cloudy with little wind. High 22C Low 11C
Tauranga - Cloudy. Not much wind. High 22C Low 15C
Wellington - Fine. Northerlies. High 17C Low 16C
(Source: MetService)
