Lanes on Auckland’s Harbour Bridge have been temporarily reduced to two in each direction due to severe wind gusts.

The NZ Transport Agency says high-sided vehicles and motorcyclists should consider delaying their journey.

A polar vortex from Antarctica is clipping the edge of New Zealand, bringing chilly weather to the whole country today including snow to near sea level in the lower South Island.

Hail, rain, freezing winds and thunderstorms are expected, with strong winds buffeting much of the country including the Auckland Harbour Bridge, and slips closing North Island roads.

Flooding has closed state highways in the North Island, while Horizons Regional Council has opened the Moutua floodgates to relieve pressure on the Manawatū River.

MetService said around 6am the Auckland Harbour Bridge was being hit by 75km/h westerly gusts. Traffic management is poised to close lanes on the bridge if needed.

The NZ Transport Agency warned drivers - especially high-sided vehicles and motorbikes - to take extra care heading over the bridge, including observing speed signs and leaving a safe following distance.

Sustained winds are forecast through the workday in Auckland before easing this evening, MetService meteorologist Ngaire Wotherspoon said.

Heavy rain, slips hit North Island travel

Heavy rain has disrupted travellers in the lower North Island, with river levels rising and slips blocking transport routes.

A slip has closed State Highway 2 near Ōpōtiki in the Bay of Plenty overnight. The road is closed between Waiotahi Valley Back Rd and Paerata Ridge Rd, NZTA said, warning drivers to allow extra time to detour.

Some passenger train services on the Kāpiti Coast are being replaced by bus after a slip came down on the tracks.

Metlink said no trains are running between Plimmerton and Paekakariki this morning. Trains are still running between Wellington and Plimmerton and between Paekākāriki and Waikanae.

Commuters are being advised to find alternative transport between Waikanae and Plimmerton if they can, or to expect delays with the replacement buses due to weather and traffic conditions.

Heavy rain has also caused rising river levels, with State Highway 53 in Martinborough closed at the Waihenga River bridge as the river peaks.

And Horizons Regional Council has opened the Moutua floodgates this morning to ease pressure on the bottom stem of the Manawatū River. The gates give water a shortcut to the sea, protecting downstream land and properties from flooding.

Traffic management is in place in the area due to floodgate operations.

The Moutua floodgates between Foxton and Shannon have been opened this morning by the Horizons Regional Council thanks to rising river levels caused by heavy rain. Photo / Supplied

Council incident controller Sarah Carswell said people should avoid low-lying areas and not enter floodwaters as there could be hidden dangers and contamination.

State Highway 56 at Ōpiki is also shut due to flooding caused by the rising Manawatū River.

Road conditions varied across the region, Carswell said.

”People should also aim to avoid the Pahiatua Track, which suffered slips and fallen trees on Sunday. While it may be open now, other routes – such as the Saddle Road – may be a more reliable option.

”There is also snow forecast to fall to about 1000 metres in the Desert Road area throughout Monday. It only takes a couple of centimetres of snow on a road to make driving dangerous, so people should avoid travel where possible until conditions improve.”

Polar blast batters country

Rough weather caused by the Antarctic polar vortex has been battering New Zealand with rain, wind and snow since Sunday, damaging properties, sparking rescues and disrupting air travel.

A rescue mission was launched yesterday afternoon after 30 vehicles became trapped at the top of Canterbury’s Porters Pass due to heavy snowfall.

Fire and Emergency NZ (Fenz) helped police and roading crews to clear the road after vehicles became stuck in the snow.

At 12.35pm, NZTA said State Highway 73 had closed from Springfield to Castle Hill due to heavy snowfall. A further area warning was in place on SH73 from Ōtira to Castle Hill.

Heavy snow on State Highway 73 at Porters Pass closed the road, trapping a number of trucks and cars on Sunday. Photo / Catherine Malone

Vehicles also became stuck outside of Arthur’s Pass heading towards Christchurch.

Police urged motorists to delay unnecessary travel on Sunday afternoon due to the poor conditions.

Road snowfall warnings in effect on Monday include;

• - Remutaka Hill Rd (SH2) – five hours from 1am-6am
• - Milford Rd (SH94) – 19 hours from 2am-9pm
• - Crown Range Rd – 17 hours from 5am-10pm
• - Lindis Pass (SH8) – 12 hours from 6am-6pm
• - Desert Rd (SH1) – 15 hours from 7am-10pm
• - Dunedin to Waitati Highway (SH1) – 14 hours from 10am-midnight

Heavy snowfall watches also came into effect for Central Otago south of Lake Wakatipu and Roxburgh, Clutha, Southland, Stewart Island, and Fiordland south of George Sound this morning, which will lapse at 5pm.

“Expect heavy snow at times above 400m, where snowfall may approach warning criteria in places,” MetService said.

Properties in lower North Island struck by flooding

Rising river levels have closed a section of State Highway 53 in Martinborough overnight. NZTA warned motorists to use an alternative route and take extra care driving around the Wairarapa.

It follows heavy rain which flooded streets on Sunday in the lower North Island, indundating properties with water.

Residents in the Manawatū-Whanganui town of Pahīatua were mopping up yesterday afternoon after a heavy downpour.

A local said blocked drains and rising creeks were to blame for the high water levels. Photos showed water creeping into homes.

Flooding in Pahīatua after heavy rain hit the Tararua Range and Wairarapa. Photo / Luke Chandler

Residential streets in Pahīatua were flooded due to the heavy rain.

Horizons Regional Council opened the Moutoa floodgates this morning due to rainfall, having warned the public it was on standby to do so last night.

The floodgates - located between Foxton and Shannon - relieve pressure on the bottom stem of the Manawatū River by diverting water down a spillway to the sea.

”The bottom stem of the Manawatū River is windy and has a relatively shallow gradient, slowing water down,” Horizons Regional Council incident controller Sarah Carswell said.

“As this happens, the channel fills, risks significantly overtopping a 30-kilometre stretch and flooding adjacent properties.”

Diverting the flood would reduce the downstream risk, but would not affect upstream water level which was a “common misconception”.

People who leased land along the Moutoa spillway were advised on Sunday afternoon that the gates could be opened, Carswell said.

”We appreciate the response these leaseholders take during flood events to move stock and drop fences, sometimes at short notice, before we operate the gates.”

The worst of the rain appeared to have passed but river and stream levels would stay high for some time.

MetService’s Wotherspoon said rain would ease off today in the lower North Island, though there would still be showers.

While most regions were battered by rain, wind or snow on Sunday, the National Institute of Water and Atmospheric Research (Niwa) reported Whakatū, Hawke’s Bay set a new August temperature record, reaching 24.6C. Records for the area date back to the 1930s.

Niwa said less than 600km to the south, Cass in Canterbury had only managed to reach 2.5C on Sunday.

Polar blast moves up country to start the week

Meanwhile forecasters are warning a polar air mass will continue to spread up the South Island and lower North Island on Monday, bringing showers, snow and hail.

“In places like Central Otago, Southland, Clutha and Fiordland, there will be frequent showers and some of the showers could have the potential to generate heavy snow around 400m,” said MetService meteorologist Josh Griffin.

“Temperatures were forecast to reach single digits in places such as Invercargill and Southland.

“The warm moist air that brought heavy rain to the top of the North Island came from the tropics while the cold fronts came directly from Antarctica.”

Weatherwatch.co.nz said a large low located to the southeast of New Zealand and an incoming high means windy weather would continue over the country on Monday and even Tuesday for some.

MetService said there was a moderate risk of thunderstorms for coastal parts of Northland, Auckland, Waikato and Waitomo before noon on Monday as the front crosses the upper North Island.

“Any thunderstorms may be accompanied by heavy rain 10 to 20mm/h and squally wind gusts 90 to 110km/h.”

There was also a moderate risk of thunderstorms for the far east of Bay of Plenty and far northern Tairāwhiti/Gisborne before dawn, and a broader area of low risk over remaining North Island areas down to Whanganui and Hawke’s Bay.