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Severe thunderstorms were lashing parts of the upper North Island tonight following chaos further south, as a powerful storm moved across the country.
According to WeatherWatch head analyst Philip Duncan, a large thunderstorm is about to reach Whakatane and has the potential to cause damage.
The Fire Service has been busy with weather-related callouts, generally minor damage such as trees falling across roads. State Highway 1 at Rangiriri in the north Waikato was down to one lane due to a fallen tree tonight.
Motorist Sue Willmore, who is travelling south, said "it looked like a tornado had gone through. There were massive trees down across the motorway. At least one car was smashed up."
A police spokeswoman said police had been called out to at least 18 incidents of trees coming down and blocking roads in the region this evening.
An ambulance spokeswoman said a car had hit a tree in Tuakau and one person was being taken to Middlemore Hospital with moderate injuries.
Meteorologists forecast severe stormy weather across the upper North Island tonight, heading out to sea by midnight.
"Some of these thunderstorms are likely to be severe...with the potential for damaging wind gusts of 130kmh. There is also a slight risk of small tornadoes," MetService forecaster Andy Downs said.
Trees and power lines were at risk of damage, and driving may become hazardous.
"Should severe weather approach, or if you feel threatened, take shelter immediately."
MetService put out another severe weather warning just after 8pm, saying "a band of thunder storms with gale force winds is moving over northern New Zealand this evening but conditions should ease from around midnight. Also heavy rain and snow in the central North Island Friday evening should clear around midnight Friday."
Auckland International Airport recorded gusts up to 100kmh, and more remote northern areas had been buffeted by much higher gusts as the rough weather hit the north tonight.
Westbound lanes of Auckland's northwestern motorway between Newton Road and St Lukes Road were closed tonight due to wind damage to motorway signs, said police.
Winds had reached hurricane force at Manukau Heads, a farming community west of Auckland Airport, WeatherWatch.co.nz head weather analyst Philip Duncan said. Gusts peaked at 154kmh.
"The Manukau Heads is a bit of wind tunnel, but hurricane force winds were recorded there for 15 minutes as the squall rolled through around 6.20 this evening," Mr Duncan said.
Thunderstorms and squalls would continue tonight.
People planning to visit west coast beaches in the Auckland region were advised to check weather warnings before venturing out this weekend.
"We're expecting large swells as a result of the MetService severe weather warning, so people need to take care as unpredictable wave surges may come through," said Muriwai Regional Park manager Scott De Silva.
The MetService forecast a 6m swell off the North Island's west coast.
Severe weather forecaster Paul Mallinson said tornadoes would most likely occur in coastal areas, but inland areas were not immune.
Snow was expected in the North Island's central high country overnight. Thunderstorms and snow were also expected to continue in the South Island, with particularly heavy snowfalls south of Mt Cook.
A heavy rain warning remained in place for Fiordland, the ranges of Westland south of Otira, and the headwaters of Canterbury and Otago rivers.
Another fast-moving front is expected to cross the South Island and move on to the North Island on Saturday evening, says MetService.
Severe northwest gales may return to parts of Hawkes Bay, Wairarapa, Wellington and Marlborough.
Taranaki chaos
The fire service has this evening been dealing with flooding in Opunake and high winds in New Plymouth have lifted a roof from a house.
MetService warned of severe thunderstorms, very strong wind gusts and possible tornadoes in Taranaki from late this afternoon.
Very strong wind gusts can break branches from trees, damage roofing, and make driving hazardous especially for high-sided vehicles and motorcycles, warned MetService.
Tornadoes can blow out windows, lift roofs, break large branches off trees, generate dangerous flying debris and blow vehicles off the road.
High winds cause problems on North Shore
On Auckland's North Shore, high winds felled a tree over a driveway and trapped residents in their home in the suburb of Bayswater this afternoon and high winds lifted roofing in Takapuna.
At Shelly Beach, north of Helensville, trees and powerlines were brought down and set a patch of grass alight.
In the Waikato, the fire service was called to a house in Te Kuiti which was being lent on by trees.
Lightning cuts power in Wellington
Lightning storms in the Wellington region cut power to more than 3500 homes today.
Ryan Auger, spokesman for Wellington Electricity, said four feeders had been struck by lightning late this morning, two at the Naenae substation and two at Wainuiomata.
Around 2000 Naenae homes were without power as a result and around 1600 in Wainuiomata.
Service crews secured the stations and began repairs, restoring power to most customers at around 12.45pm, said Mr Auger. "But still about 500 customers in Naenae have no supply. We expect the majority of the customers to be back on by late this afternoon."
Power was restored to the last houses at around 5.20pm.
Emergency services have also been kept busy in the Hutt Valley today, with lightning setting a shed on fire in Avalon and high winds bringing down trees and powerlines.
Mike Wanoa, shift manager at the Fire Service's Wellington communications centre, said flooding was also causing problems in the Wairarapa and Kapiti Coast regions.
Mr Auger said it was likely more powerlines would come down in the next 12 to 24 hours. He advises people who see downed powerlines to assume they are live and call Wellington Electricity on 0800 248 148.
The Met Office said there were 109 lightning strikes in the Wellington region today and meteorologists are forecasting more severe thunderstorms and possible tornadoes as two fronts move across the North Island later today.
'Line of thunderstorms'
"There is a band of thunderstorms, with the potential to create large wind gusts, edging its way towards New Zealand," MetService operational manager Steve Ready said earlier today.
"The line of thunderstorms is lying just to the west of the South Island and is expected to hit the North Island this afternoon."
Mr Ready said the thunderstorms and wind gusts of up to 130km/h would not be widespread.
"They will pop up here and there.
"The westerlies generated over most of the North Island will be very large and they are going to get stronger as the afternoon goes on."
Mr Ready said the storm would come in waves over the weekend.
"There are several pieces to it. The frontal system moving over the North Island will drop and then surge again tomorrow morning."
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AA roadwatch
People are advised to be careful while out and about and to cut down on travel. Those planning to travel on the Desert Rd should be careful of heavy snowfall in the area, and drive to the conditions.
Similar warnings have also been issued to those planning sea trips, while the New Zealand Mountain Safety Council has advised those planning trips in the outdoors to hold off until the weather has eased.
Rough seas
Mr Ready said the seas would be rough on the west coasts of both islands, peaking at their roughest tonight.
"They are expected to drop but will stay high over the course of the weekend."
Mr Ready said swells were expected to be between 4-5m today, and 6-7m in some places tomorrow morning.
He said the weather would not start to clear until the middle of next week.
WeatherWatch.co.nz head weather analyst Philip Duncan said that the weather would not be as severe as a hurricane or cyclone, partly because the low-pressure system would be spread evenly and over a large area rather than tightly wrapped around a small centre.
Auckland Civil Defence warned Aucklanders to stay up-to-date with weather forecasts over the next 24 hours.
Group Controller Harry O'Rourke said Civil Defence and local authorities were monitoring the situation.
He reminded people to check their emergency kits and plans.
Oil platform
Meanwhile the Maari oil platform, which is 80km off the coastline of southern Taranaki, is getting prepared from the impending storm.
OMV New Zealand, who operate the platform, said they have "no current cause for concern regarding the Maari oilfield facilities, and is not anticipating any major impact on production".
In preparation for the storm the company has postponed non-essential maintenance and outside engineering work.
"The Maari facilities include the Wellhead Platform (WHP) and the FPSO Raroa. They have all been designed to cope with a storm of this size, and more," OMZ said in a statement. "The WHP is firmly embedded in the seabed, and rises 30 metres above sea level, well above the projected maximum wave heights in this storm."
