An emergency warning has gone out to coastal residents near Thames to be wary of flooding as the combination of a king tide along with a low pressure front hitting the country is raising tides to abnormal heights.
Police received some reports of flooding in Auckland, prompting a warning to motorists to follow the directions of Auckland City Council and Transit contractors who were working to highlight the danger spots.
Lanes on the Northern Motorway (State Highway 1) and the Northwestern Motorway (SH16) were closed by high tides and later reopened.
Waikato Civil Defence Group emergency management officer Greg Ryan said the combination of a king tide, a weather system bringing strong north easterly winds and a storm surge will result in abnormally high tides over the next day.
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A king tide occurs when the Sun and the Moon are aligned at the closest points to the Earth, resulting in the largest tidal range seen throughout the year. They can be magnified by extreme weather events.
'It is possible we will see tides similar to January last year, when low-lying coastal properties and roads on the western Firth of Thames were affected,'' Ryan said.
'If you live in low-lying areas on the coast and experienced flooding on your property in January last year, do what you can to minimise the risk of similar damage occurring again.''
Ryan said If the flooding occurred, it would be about the time of high tide at 8pm. As well as causing flooding, the conditions could result in coastline erosion.
Thames Valley emergency operating area manager Gary Talbot warned floodwaters often carry debris, making it dangerous to enter in a car or on foot.
''If you are travelling along low-lying coastal roads be aware of the possibility for floodwaters, which may be deep or make road surfaces slick,'' he said.
Debris may also be present after waters have receded, he said.
''If you don't need to be on these coastal roads tonight, then we'd urge people to stay home.''
He said residents in the area should call 111 if they needed immediate assistance.
Meanwhile, large areas of the South Island are bracing for heavy snow as a band of stormy weather bears down on New Zealand.
MetService is warning that up to 100cm of snow could accumulate above 300 metres in Canterbury and Marlborough, although it has cancelled severe gale warnings for parts of the lower North Island and Marlborough Sounds.
"This is likely to be a highly significant snow event for Canterbury and Marlborough making travel very difficult and causing stress for livestock. Heavy snow could also damage structures such as powerlines," MetService said.
The snow would be brought to the area by a sharp front that was expected to lie over the central South Island this evening.
In Canterbury and Marlborough south of Seddon rain was expected to turn to snow late this evening or overnight. In the 27 hours from 9pm, 50cm to 100cm of snow may accumulate above 300 metres, while south of about Lake Tekapo between 10cm and 40cm was expected.
Between 10cm and 40cm may also accumulate in the area from 100 metres to 300 metres, while lesser amounts may fall to near sea level.
The front was also expected to also bring heavy rain to Westland from Hokitika northwards, Buller and northwest Nelson. In the 36 hours from midday today between 120mm and 180mm of rain was expected.
In Westland south of Hokitika heavy rain was developing this morning, with between 80mm and 120mm expected in the 21 hours to 6am tomorrow.
Another front was expected to bring a burst of heavy rain to the eastern Bay of Plenty and northern Gisborne, with 70mm to 100mm expected in the 15 hours from 3pm today, MetService said.
Northerly winds were expected to reach gale force this afternoon in southern Taranaki, Wanganui and Taihape, with gusts of 130kmh possible from 1pm to midnight.
In Nelson, Buller and Westland north of Hokitika southeasterlies were expected to rise to gale tomorrow morning and ease by the evening, with gusts of 130kmh possible in exposed places.
Severe gale warnings had been cancelled for Wellington, Wairarapa, the Marlborough Sounds, Gisborne and northern Hawke's Bay, although northerly gales were still expected to affect those areas from this afternoon.
The fronts bringing the nasty weather are associated with a deep low expected to approach the upper South Island from the west early tomorrow and move onto the country late in the day.
TRANSIT OF VENUS
The stormy weather outlook was lowering chances of seeing the last Transit of Venus for more than a century.
The planet will be passing in front of the Sun from 10.15am to 4.43pm tomorrow. After that it will not do so again until 2117.
It is unsafe to view the event with the naked eye, but if by some lucky chance skies clear it can be seen through special shaded viewers to protect the eyes or through specially adapted telescopes.
The superintendent at the University of Canterbury's Mt John University Observatory at Lake Tekapo, Alan Gilmore, said New Zealand was likely to miss the rare astronomical event.
"The weather forecast for Wednesday is pretty dire for the whole country. The best place to view it could be online," he said.
New Plymouth Astronomical Society member Rodney Austin was hoping a break in the clouds could give him a glimpse of the transit.
"Next time it happens I'll be 172," he lamented.
"The weather that has been predicted is wind and rain. You hope there will be a break in the cloud so you can possibly see it."
Southland Astronomical Society president Steve Butler was also living in hope the weather would clear up for some of the day.
If there was a chance of seeing the transit, he would be setting up his telescope, equipped with a sun filter.
"You will be able to see things like sunspots on the face of the Sun as well as Venus itself," he said.
Other astronomers would be using binoculars so the transit could be projected on to paper for safe viewing.