Thunder expected before sun will come out for Christmas Day

Rain and thunder are expected for parts of the country before settled weather arrives for Christmas. Photo / Warren Buckland

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.

SH 6 Inangahua to Westport: Surface water is affecting the road at the moment. Please drive to the conditions.^SM https://t.co/mLySiNnbQp pic.twitter.com/qDvuzeR1oV

— Waka Kotahi NZTA Canterbury & West Coast (@WakaKotahiCWC) December 21, 2016

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.

Gusty northwesterlies in Canterbury are expected to ease during the afternoon and northwesterlies through Cook Strait will ease in the evening.

Temperatures in the east of the North Island could be in the high 20s, perhaps even early 30s, Duncan said.

Tomorrow, showers were expected in the afternoon, especially in inland areas, from Canterbury northwards in the east and in the eastern parts of the North Island.

"These showers may become heavy with a chance of hail, thunderstorms possible too, mainly about Marlborough and the Wairarapa," Duncan said.

On Christmas Eve on Saturday, there was "no risky weather to speak of", Duncan said.

"Cloudiest conditions will likely be along the West Coast of the South Island and about Southland, there may be a shower about these regions from time to time also otherwise it's a mainly dry day."

Southwesterlies are likely to be fairly breezy about Taranaki through to Northland in the west. West to southwesterly winds could be gusty in coastal Southland.