Wild weather: Severe thunderstorm watch and chance of small tornado

Aucklanders heading home from work and out and about this evening should take extra care with a severe thunderstorm watch in place and the chance of small tornado.

Metservice has issued a weather watch for severe thunderstorms over Northland, Auckland, Great Barrier Island, and the Coromandel Peninsula this evening, with localised downpours of 25 to 40mm/hr, strong wind gusts of 90km/h and a chance
of small tornado.

Surface flooding may occur in some low-lying areas from short periods of intense rain.

Metservice Meteorologist April Clark said, although they may be brief, some of these falls could be very heavy for some places.

"We are expecting that front to move over Auckland as we head into the evening, so people need to be careful if they are going out and about," she said.

NZ Transport Agency is warning motorists in Auckland of reduced visibility due to the weather.

"Extra caution is advised this afternoon with heavy rain and thunderstorms forecast for the region. Currently there is some reduced visibility on the network, please remember to switch on your headlights and drive to the road conditions," it said.

Heavy rain with embedded thunderstorms are also expected over the Bay of Plenty and Rotorua this evening and overnight.

The thunderstorms come with an active front that raced across the South Island this morning and continues up the North Island this afternoon and evening.

Metservice Meteorologist April Clark said the front has passed through Wellington, which had a strong wind warning in place until 1pm, and is now lying over the Taranaki, Waitomo region.

"There is a lot of widespread rain over the rest of the North Island. With that front we do also have a few places on heavy rain watch and warning," she said.

Heavy rain warnings are in place for Bay of Plenty east of Opotiki, and the ranges of Gisborne, Mount Taranaki and the Tararua Ranges.

Heavy rain watches are also in place for Coromandel Peninsula and Bay of Plenty from Opotiki westwards, Waikato, Waitomo, Taumarunui, Taupo and Tongariro National Park, and North Taranaki.

Strong wind watches were in place in Fiordland south of Dusky Sound, coastal Southland and Stewart Island until 3pm today.

Eastern Bay of Plenty and the Gisborne ranges will be the last to see heavy rain clear early tomorrow as the front weakens and moves away to the east.

Behind the front, rainfall significantly decreases - if not ceases - but so will temperatures nationally.

Eastern coasts will see the greatest drops with uninterrupted southerlies dragging cool air from the Southern Ocean.

Some inland areas may even see early morning frosts, with Blenheim's overnight temperature on Wednesday set to drop to 3C, the lowest since last spring.

This cool change is set to last over the country for the rest of the week.

While a ridge of high pressure starts to build over the South Island and eastern parts of the North Island tomorrow, bringing dry weather, the east and upper North Island is set to hold on to a few showers in the southeast flow.

"During Thursday and Friday another front is forecast to sweep across New Zealand, cementing a cooler and changeable weather pattern which is typical at this time of year," Clark said.