Snow, wind and rain warnings; some Cook Strait ferries cancelled

More wild weather is on the way with both islands in for a lashing of rain over the next few days, snow forecast for the South Island and ferries cancelled across the Cook Strait.

Orange heavy rain warnings are in place for Gisborne/Tairawhiti, Kaikoura, Banks Peninsula and Canterbury. Road snowfall warnings have been issued for Arthur's Pass and Porters Pass, while heavy swell warnings are in effect for the Wellington and Wairarapa coasts.

Gisborne in for a dousing, following a relatively settled period

Tairāwhiti residents north of Tolaga Bay are being told to prepare for heavy rain, amid a quieter year for weather warnings.

MetService has issued an orange heavy rain warning for the 12-hour period until midday Wednesday.

The forecast is for 70mm to 100mm of rain, with peak rates of 15mm to 25mm an hour expected on Wednesday morning, causing rivers to rise, and potentially surface flooding and slips.

Deputy civil defence coordinator Nori Parata said it had been a pretty quiet year for storms, aside from a period of intense rain a couple of weeks back - and she was glad for it, as there was a risk of constant warnings becoming less effective.

"There's a danger of becoming the boy who cried wolf with so many possible events," she said, "So it's nice to have had a break and for the community to hear the messages refreshed, rather than, 'Oh no, not another one'."

She said during weather warnings, they checked in on homes in known flood-prone areas, where there were a number of families who had remained in stickered properties damaged in past weather events.

"Because despite all the coloured stickers that people were getting, some people just couldn't afford to leave their places," she said. "But those families are very good at their safety plans."

She said the ground remained sodden from rain over the past month, and temperatures had cooled off, so things weren't drying as quickly.

As the principal of Tologa Bay Area School, Parata said the main concern was children getting to school, and then home again.

"Sometimes they can get to school, but then things turn for the worse, and it's how do you get them home safely before the roads are really impacted?"

A brief heavy rain watch for Northland ended at midnight on Tuesday.

A windy Thursday on the cards for Wellington

Further south, the capital is forecast to receive strong winds along the south coast, including Wairarapa north of Castlepoint, causing ferry cancellations.

MetService has issued heavy swell warnings for the 33-hour period between midday Thursday until 9pm Friday.

Waves of 6 metres were forecast off Wellington - Cape Terawhiti to Turakirae Head from 3pm Thursday to noon on Friday. Swells rising to 7 metres were expected off Wairarapa - Turakirae Head from midday Thursday to 9pm Friday.

"This weather system that's bringing all of this weather that we're expecting is also going to be generating some large swells, but also the wind's generating some large waves on top of that and causing all sorts of problems and disruptions," MetService meteorologist Mmathapelo Makgabutlane told RNZ's Morning Report.

Interislander said it had cancelled crossings from 8.30pm Wednesday through to 2.30am on Friday, and there would be extra sailings put on over the weekend to accommodate those passengers.

It said more cancellations were likely on Friday if conditions did not improve.

Bluebridge was cancelling sailings from 1.30pm on Wednesday and all of Thursday.

Cold blast hits South Island

Orange heavy rain warnings for Banks Peninsula and the region north of Amberley kicked in at 4am Wednesday for 38 hours, with the heaviest falls expected in the evening and on Thursday morning. MetService said there was a moderate chance of upgrading to a red warning.

An orange warning also covered the Kaikoura Coast and ranges, which were in for 150mm to 200mm of rain from midday Wednesday to 6am Friday, with snow lowering to about 1000 metres on Thursday.

The snow would be welcome news to ski fields, Makgabutlane said.

"At this early stage, I'm sure we'll definitely take any snow that we can get. However, it is quite unseasonal, so in terms of the ski fields, we'll definitely be crossing our fingers for more snowfall as the season goes on."

Christchurch and Canterbury south of Amberley are under a heavy rain watch, while there is a heavy snow watch for the high country south of the Rangitata River and road snowfall warnings for the Porters and Arthur's Passes.

"For places like Canterbury, it is looking like quite a long-lived wet weather story," Makgabutlane said.

Strong wind watches have been issued for the Buller, Grey, Westland and Nelson Lakes districts, the Marlborough Sounds and Wellington.

MetService said the prolonged rain came after a wet start to the year, and warned it could lead to rapidly rising rivers, surface flooding and difficult driving conditions.

Christchurch City Council contractors had been preparing ahead of the downpour, clearing gutters, sumps, stormwater grates and beach outfalls.

The heaviest rainfall was expected in the western Port Hills and the southern part of Banks Peninsula, the council said.

"It's a good idea to clear your rain guttering and drains and if you know there are leaves blocking sumps or drains by your property, it would help us if you could remove them, and put them in your green wheelie bin," the council said.

"Our stormwater network is designed to cope with heavy rain and our road network is also part of our stormwater network playing an important role during wet weather events. In most parts of the city our roads have been designed as secondary flow paths for stormwater so in heavy rain its normal to see some flooding on our roads."

The council was also managing water levels in the Ōpāwaho Heathcote River.

"Residents along the upper and mid-reaches of the river can expect fluctuations of water levels at any time before, during and after the rainfall event, even during periods of dry weather. This is to reduce peak flood levels during the rainfall event by maximising the use of the storage volume in the basins," the council said.

Makgabutlane said by the weekend, conditions should start clearing up.

"It is expected to be at least a couple of days. And so today, Wednesday, we're expecting everything to really start kicking off. Tomorrow, Thursday, will be another day to keep a close eye on, as well as Friday…

"But it does look like as we head into the weekend, most of the country should be rid of that weather and by Sunday, things are looking pretty good across the country."

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