Christmas Day is expected to be settled, but thunderstorms and heat are expected in the lead-up to the big day.
Surface flooding due to heavy rain has already hit the South island with NZTA warning motorists to drive carefully on State Highway 6 between Inangahua and Westport on the west coast.
WeatherWatch head analyst Philip Duncan said earlier a front pushing northwards over the South Island today meant rain in northwestern parts.
Heavy showers were possible in the late afternoon for eastern Otago through into South Canterbury and parts of the upper North Island. There was a chance of thunderstorms and hail in the lower South Island.