MetService warned that torrential rain could cause surface or flash flooding near streams, gullies and urban areas and make driving conditions extremely hazardous - while large hail could significantly damage crops, orchards, vines, glasshouses and vehicles.
Tornadoes could blow out windows, lift roofs, break large branches off trees, generate dangerous flying debris and blow vehicles off the road
Meanwhile, MetService has issued weather warnings for much of the west coast of the South Island, as well as Horowhenua, about and south of Levin, Wellington north of the Ngauranga Gorge, and the Tararua Range.
Heading into tomorrow, there was also a risk of thunderstorms across much of the central and southern North Island, including coastal Waitomo and Taranaki to Southern Manawatu.
The highest risk of thunderstorms was about northern Fiordland, Westland and Buller.
Thunderstorms in these areas are expected to become more frequent as the afternoon went on - and could bring brief heavy rain, hail and wind gusts up to 110km/h.
There was also a risk the thunderstorms could spread into inland Buller, Tasman and Nelson and the Marlborough Sounds.
In other parts of the country, there was a low a risk of thunderstorms. This included parts of Southland and Clutha, the Canterbury foothills and other parts of Marlborough, Wairarapa and other western North Island areas from coastal Waikato southwards.
Metservice said it would take time for the current wet weather to pass, with many rainy days expected this week and throughout next week for many places.
After cloudy days in Kaitāia and Auckland today, the rain sets in tomorrow and persists to various degrees over the next week.
However, in Gisborne, the sun is forecast to make much more of an appearance, with mostly cloudy or fine days over the next week.
In New Plymouth, the rain comes tomorrow and stays all week, paired with some thunderstorms possible over the next week.
In the capital, MetService's forecast includes rain until early next week. On Sunday, severe gale northwesterlies are forecast.
The weather in Christchurch is a mixed bag over the next week, with some rainy days between cloudy or fine days.
In Invercargill, MetService has forecast mostly cloudy days with a few showers over the next week.
Meanwhile, the forecaster said there was also a moderate risk of thunderstorms over the Chatham Islands this evening.
