MetService is warning of torrential rain, gales and snow for parts of the country overnight and into tomorrow as a severe storm strengthens across the Tasman Sea.
The agency said a severe storm strengthening across the Tasman Sea would bring heavy rain, thunderstorms and strong wind gusts to most parts of the country.
It also expects snow in parts of the South Island, with Arthur's Pass likely to get a dumping of up to 1m deep by tomorrow afternoon.
Porters and Lindis Passes would also get snow.
Rain would be heaviest in the Buller, Nelson and Marlborough regions in the South, and Taranaki in the North.
Northland, Auckland, Taranaki, Whanganui, Taihape and Manawatu were expected to be hit with severe northerly gales.
The National Institute of Water and Atmospheric Research (NIWA) said steady rain would spread over the middle of the country by this evening.
That rain would turn to torrential downpours sweeping across the top of the northern Tasman, Nelson and parts of northern Marlborough tonight.
In the North Island, rain would be heaviest in Taranaki, Manawatu-Whanganui and Wellington, with more than 100mm overnight in places, possibly causing surface flooding and slips.
Early tomorrow morning squally rain and wind is forecast to pass through the north of the South Island with southern and western parts of the North Island lit up by frequent lightning.
Wind gusts may be higher than 130 km/h in places - a level typical of category two tropical cyclones. The worst of the wind will pass through Wellington between 3am and 6am.
Stormy weather in Auckland
The squall line of heavy rain and thunderstorms is forecast to move through Auckland tomorrow morning, with winds gusting to at least 100km/h. But by midday, skies will clear in Auckland, heralding a warm but windy afternoon.
Tomorrow night heavy rain and possibly damaging winds will hit the west of the North Island with rain likely to exceed 100mm overnight, leading to surface flooding and slips.
Mid-Canterbury, including Christchurch, will also have heavy rain early tomorrow with strong wind gusts moving inland during the afternoon.
Tomorrow night yet another round of heavy rain and strong, possibly damaging winds could hit the west of the North Island.
Sunday will continue to be unsettled, with gusty showers across the North Island and isolated showers and chilly temperatures in the South Island.
On Monday much of the country will continue to have windy, chilly weather with showers.