Heavy rain and wild winds are lashing much of New Zealand, with Auckland commuters being urged to delay travel this morning to avoid the worst of the storm.
Niwa has warned that a month's worth of rain may fall in parts of the North Island and in the northern and eastern parts of the South Island.
A deep low and associated rain-bearing fronts is moving down the North Island, to encompass the whole country.
Severe weather warnings have been issued for most of the North Island and much of the South.
Road closures have already hit parts of the Canterbury high country with State Highway 73 from Springfield to Castle Hill closed as well as Aoraki Mt Cook Highway and SH8 between Fairlie and Lake Tekapo.
The wintry blast is being attributed to an "atmospheric river" snaking across the country. These long, thin filaments of atmospheric moisture are capable of carrying double the average flow of the Amazon River – or 200 times that of our largest river, the Clutha/Mata Au.
The west coast of the top of the South Island is also forecast to experience severe winds. They are expected to rise to a gale gusting at 140kmh.
Nelson and Marlborough districts will also be battered by rain and wind.Canterbury's high country is under a heavy snow and rain watch, with heavy rain expected to turn to snow above 400m.
Central Otago and the Lakes district can expect similar conditions.
Several roads have heavy snow watches in place between Tuesday and Wednesday. These are: Lindis Pass, the Crown Ranges, Arthur's Pass, Porter's Pass, and the Dunedin and Waitati Highway.
MetService Forecaster Aidan Pyselman said the system would likely move off to east of the South Island tomorrow. He said it would clear up around the North Island especially, but then another low would move in from the north on Friday morning.
Waka Kotahi is closely monitoring the weather, and is warning of potential closures to Auckland's Harbour Bridge.
MetService has issued a strong wind warning for Auckland from 2am until 9am today, with gusts of up to 110kmh forecast to strike during the morning rush hour.
Waka Kotahi is warning Auckland motorists to avoid using the Harbour Bridge over this time as wind speeds may surpass the threshold for safe use, and could result in multiple closures.
"Motorists are urged to plan ahead as the predicted closures could coincide with peak morning traffic."
Drivers of high-sided vehicles and motorcyclists are encouraged to avoid the bridge while wind warnings are in place and use the Western Ring on State Highways 16 and 18.
Auckland Transport was warning of disruptions to bus services on the North Express and on services from Glenfield, Beach Haven and Takapuna.
Ferry passengers are also being told to expect potential disruptions and are asked to delay to their travel if possible.
"On windy and choppy days like tomorrow ... our ferry operators often cancel trips or replace them by road depending on the conditions.
The harsh weather is the result of a deep low moving across New Zealand, bringing with it associated fronts which cause the conditions.
Between Coromandel and Bay of Plenty, people can expect winds approaching gale-force and up to 110mm of rain, with rates of 15mm per hour at times.
Flooding is likely for many parts across the Waikato region. This is due to the heavy rain falling on already saturated catchments.
River flooding along low-lying coastal areas may also be exacerbated over high tide periods for all Waikato region coasts. The regional council has asked residents to stay vigilant for localised flooding and slips caused by the high river and stream levels.
Gisborne to Hawke's Bay can also expect similar conditions, with heavy rain. And at the bottom of the North Island, Wellington is set to experience gale-force winds until at least Wednesday morning.
