Ferry crossings have been cancelled as strong winds and large swells batter the Cook Strait, with MetService issuing a gale warning.
Interislander had earlier cancelled two of Sunday's sailings between Picton and Wellington, as well as two trips on Monday.
But it said on Sunday night that all sailings were now on hold until conditions eased, because southerly swells were higher than forecast.
Kaiārahi had been due to leave the Marlborough Sounds in the evening, but had instead returned to port in Picton to wait for the swells in the Cook Strait to ease, a spokesperson said.
"We anticipate this will happen in the coming hours.
"Kaiārahi is currently berthed in Picton where conditions are calm and still. There are approximately 500 passengers on board, they are being looked after as they wait."
According to the ship tracking website MarineTraffic, Kaiārahi got underway from Picton just after 11:30pm.
Kaitaki, which was due to leave Wellington at 8:30pm with more than 800 passengers on board, was also in a holding pattern.
In an email sent to passengers just after 10pm, seen by RNZ, Interislander apologised for the inconvenience of the delay.
"We will be commencing loading asap but will not be leaving Wellington until the Master is comfortable to depart due to rougher sea conditions than forecast - this could be at least 4 HRS," the email said.
"If you wish to not travel tonight please advise staff but keep in mind that our ships are fully booked for the next week."
According to MarineTraffic, the Kaitaki finally set off about 1am Monday.
Aratere sailings on Monday morning (at 6:15am from Wellington and 11am from Picton) were cancelled, but scheduled Kaitaki and Kaiarāhi sailings were expected to go ahead, the spokesperson said.
Meanwhile Bluebridge had cancelled three sailings on Sunday, and four on Monday, with further cancellations likely.
It said conditions were likely to remain unsettled until Monday evening.
Snow in summer
A video provided to RNZ showed snow falling at 10:30am on Sunday.
"I am on the Desert Road of New Zealand, and it is summer, and it is snowing.
"This is the most ridiculous thing ... global warming, it is a thing."
MetService meteorologist Alwyn Bakker said it was an unusual if brief display.
"At around 10am, there was a bit of snowfall on the Desert Road.
"It looks like light flakes rather than anything settling. The temperature dropped to just about freezing. It hasn't picked up.
"Briefly there was a bit of a snow flurry, so that's unusual for this time of the year, it being nominally summer, but of all the places in the North Island for it to happen, the Desert Road's a pretty likely bet, it's quite high altitude compared to a lot of other places.
"Being inland, it does get those cooler temperatures than the coastal regions where the ocean has more of a warming effect."
Another email sent to RNZ reported snow on the ground in Napier, which the sender described as "crazy".
However, Bakker said reports that snow fell in Napier were unlikely because the region had not been cold enough.
Summer sun set to return
This Christmas period cold snap comes after an "exceptionally warm" December, according to National Institute of Water and Atmospheric Research (NIWA) meteorologist Chris Brandolino with everywhere - bar two locations on Rakiura Stewart Island - seeing above-average temperatures.
Warmer temperatures and drier weather were set to return in the second half January.
So far the summer was "mixed", Brandolino said, but it was far from over.
"There was very warm, hot weather in December and that seems so far away now.... There's no doubt about it we are seeing a change in the weather pattern. We're seeing more air flows from the south and southwest, and as a consequence, our temperatures have responded by going down."
The change in airflows since Christmas had "brought about some beneficial rains for places like eastern portions of the North Island, who are recovering from some really significant, profound dryness".
Unfortunately, it had "come at the cost of some enjoyable summer weather", Brandolino said.
Mōrena, Aotearoa
— MetService (@MetService) January 4, 2025
We've got a mixed bag of temperatures to expect later today. The east coast of both islands will be on the cooler side (for summer) with temperatures of 16-19°C, while the north and west will hit those 20s
Wanaka is the place to be if you like the heat,… pic.twitter.com/laeCo4QQfZ
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