One week out from Christmas Day, forecasters are predicting a warm day with a possibility of rain.

The accuracy of the Christmas Day forecast will increase as the day draws nearer, but currently a high pressure system centred to the east of the country, near the Chatham Islands, is a dominant feature on MetService computer models, while a front sits to the southwest of New Zealand.

MetService meteorologist John Law said the set-up would leave the country with a northerly feed of air, resulting in average or slightly above average temperatures.

Showers were forecast as possible over the North Island, especially in the north and west, and also for the West Coast of the South Island, he said.

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"There has been some very good agreement in the computer model guidance over the last few model runs.

"However, as we know in New Zealand, subtle changes in the pattern can cause very different weather."

MetService forecasters would be monitoring data from multiple computer models and satellites between now and Christmas Day, as well as from thousands of radar images and observations across the country, Mr Law said.

"As per usual, the forecast room will be operational 24 hours a day right through the Christmas period."