As the unusually warm May weather the country has been enjoying comes to an end, MetService is warning of downpours, gale-force winds and even snow in many areas.
The wild weather that hit parts of the lower North Island and upper South Island on Saturday night is likely to worsen in other parts of the country in the coming week.
MetService says wind gusts of 120 kilometres an hour or more are possible in exposed places from Hawke's Bay to northern Wairarapa on Sunday evening.
In the South Island, westerly gales and heavy, squally showers are forecast for southern and western regions.
Snow is also forecast, with falls down to 300 metres on Sunday night in parts of Fiordland, Southland and Otago.
MetService says heavy falls are possible in the hill country of eastern Southland and Clutha and may affect higher roads, including the Milford Road.
Severe wind gusts of 120 kilometres per hour are also forecast for coastal Southland as far north as Otago Peninsula, and farmers have been advised to shelter any vulnerable livestock.
Trampolines swept into air
MetService says bursts of heavy rain and thunderstorms hit Nelson and Buller on Saturday night, and gusts of up to 80 kilometres battered parts of Wairarapa, Wellington and Marlborough.
The Fire Service in Wellington says it was inundated with weather-related phone calls. Police said there was light flooding around the city, but no reports of serious damage.
In Nelson, two trampolines were swept into the air.
Auckland's highest-ever May temperature
Climate scientist Jim Salinger says the La Nina conditions that have been causing the warm weather are tapering off.
After the cold spell, he says, temperatures will begin to rise again around Wednesday, but they will not reach the same highs as before.
Dr Salinger says the first half of this month has been unusually warm, with Auckland recording its highest-ever May temperature of 24.6 degrees on Saturday.