Forecasters are predicting warm weather for Christmas Day, but unwelcome surprises can't be ruled out.

High pressure is expected to move over the country and leave a pleasant subtropical front in the lead-up to Christmas.

But WeatherWatch Head Analyst warns some rain could affect New Zealand's West Coast and spill over into the South Island and lower North Island.

"It's not locked in, we're on the edge of a system, but I think at this stage- high pressure's more powerful in December- hopefully at least over half the population should have a pretty good Christmas."

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