Weather: Thunderstorms racing towards New Zealand

NIWA is warning Kiwis to "shut the windows" before going to bed on Saturday night as thunderstorms race towards the upper North Island.

"We have our eyes on a squall line that is expected to cross the Tasman Sea on Saturday night and arrive in the upper North Island early Sunday morning," NIWA says on Facebook.

"It could bring brief strong winds and downpours before sunrise (good timing!) on Sunday, with the risk primarily in Northland, Auckland, and Waikato."

More than 328,000 lightning strikes have been recorded over the Tasman Sea in the past 24 hours as the thunderstorms move towards New Zealand.

On Sunday, WeatherWatch says the North Island will be colder in the lower half and milder in the northern half, with a mixture of rain, showers, drizzle and dry spells.

Meanwhile, the eastern South Island will have a cold Sunday with single-digit highs, some barely breaking past highs of 5C to 7C.

"Sunday is a great example of spring - it will be cold in the South Island and lower North Island while a low with mild nor'westers affects the upper North Island," WeatherWatch says.

"One interesting note is that as this cold southerly collides with the mild rain over the North Island it will turn that rain to snow over the Central Plateau. Heavy snow is expected around the Central North Island mountains and ranges and some snow might impact the Desert Road and plateau from Sunday to Tuesday."

Newshub.