A cold blast from the Southern Ocean is moving across New Zealand on Wednesday and Thursday, delivering dangerous waves, cold temperatures, thunderstorms, low-level snow and gale force winds.
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"An unstable cold southwest flow sweeps up Aotearoa today and into Thursday, and has resulted in many severe weather watches being issued this morning," MetService says.
Thunderstorms
"This cold air mass is especially unstable and this thunderstorm outlook chart reflects this," MetService warns.
"The severe thunderstorms could lower snow to sea level, bring large hail accumulations and localised heavy rain."
A severe thunderstorm watch has been issued for Christchurch and the Canterbury Plains between 3pm-11pm today.
Low-level snow
"Snow is expected to quite low levels on Wednesday-Wednesday night... a few flakes could even fall to sea level in the South Island!" NIWA says.
MetService has issued a heavy snow watch for Fiordland on Wednesday with snow down to 100 metres in the afternoon. Snow to low levels is also forecast for Southland, Clutha and a number of the alpine passes.
WeatherWatch says a few flurries are possible around Queenstown and maybe the Dunedin hilltops.
Gale-force winds
Strong cold southwesterly winds will surge up New Zealand on Wednesday and will peak later in the day.
"Winds peak during Wednesday PM with gales pushing in and gusts exceeding 100km/h in exposed areas, or the usual wind tunnels," WeatherWatch warns.
"While Thursday is a blustery day with gales in some locations the peak winds do ease back as the day wears on.
Strong wind gusts can damage power lines, and Vector's head of network field services, Marko Simunac, says Vector has crews ready to respond to any power outages in Auckland.
"Our response crews and storm management teams are ready to respond and we are actively monitoring the latest weather advice and our own data on network performance," he says.
Simunac says that if the weather causes any power lines to come down, Vector will shut down power to that area as a public safety precaution until crews arrive on site.
"We remind people to stay away from damaged electrical equipment and report issues by phoning us on 0508 VECTOR," he says.
"All lines should be treated as live at all times. If you see any damaged power equipment or power lines down, please keep a safe distance away and report it to us as soon as possible on 0508 VECTOR."
Peak winds are in the 24 hours from noon on Wednesday to noon on Thursday nationwide and may be gustiest with squally showers.
Dangerous waves
On top of the wind and cold, WeatherWatch says the seas will be rough with "dangerous waves" on southern and western coastlines.
"People should take extreme care on the western side where waves may exceed seven metres, including popular places like Taranaki, western Waikato and west Auckland," it says.
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