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The worst of the wild weather is coming with heavy rain, gale-force winds, thunderstorms and even small tornadoes forecast in parts of the country.
MetService meteorologist Micky Malivuk said a "disturbed weather pattern" was over the country this week.
A cold front was making its way onto the bottom of the South Island this morning, bringing heavy rain and thunderstorms to the West Coast, and winds up to 130kmh through the Canterbury high country.
Conversely, temperatures have dropped below 0degC at the bottom of the country, and most southern spots will struggle to make it into double digits over the next few days. Snow is forecast down to 400m in places.
Road snowfall warnings are in place for Milford Rd (SH94) and the Crown Range Rd, where another few centimetres are forecast this afternoon.
Snow showers may also affect higher parts of the Lewis Pass road for a time later today.
A brief period of snow or sleety showers may affect the summit of the Dunedin to Waitati highway between 8am and noon tomorrow.
This system will arrive in the North Island late morning and intensify during the day.
The heaviest rain today is expected in Fiordland, Westland south of Otira, and the headwaters of Otago and Canterbury Lakes and Rivers, where 100-150mm could fall. Warnings are in force.
Auckland and Northland are already being affected by another front this morning, bringing showers - at times heavy - and thunderstorms through the day, but temperatures will remain moderate at 18degC and 20degC respectively.
Northwesterly winds could reach 130kmh in the Canterbury high country through to this evening, spreading north to Wairarapa from about Masterton southwards, Wellington and Marlborough until 11pm.
There is a moderate risk of thunderstorms this morning in western areas of Northland, Auckland, Waikato and Waitomo this morning, with potential for heavy rain and small hail.
Taranaki, Taupo and Bay of Plenty northwards could also see some thunderstorms.
The risk of thunderstorms spreads over the whole of the upper North Island by this afternoon and evening, with higher chances about eastern Bay of Plenty.
In central New Zealand the main thunderstorm risk in Westland, Buller and Nelson will be this afternoon and evening, and over the Marlborough Sounds, Wellington, Kapiti, Horowhenua, Taranaki, Waitomo and Taumarunui in the evening and at night.
These thunderstorms will be accompanied by localised heavy rain, small hail, strong wind gusts and possibly one or two small coastal tornadoes.
The country is in for a similar weather pattern over the next week, Malivuk said.
"We are in for a very unstable, very showery period."
On Thursday another front is expected to sweep east onto the country bringing more heavy rain to western areas from Fiordland to Taranaki.
Another front moves east onto the country Saturday bringing even more heavy rain to western areas.
Auckland Occasional showers, some possibly heavy. Northwesterlies becoming gusty this afternoon. 18degC high, 11degCovernight.
Hamilton Occasional showers, some possibly heavy. Northwesterlies becoming gusty this afternoon. 17degC high, 9degC overnight.
Tauranga Occasional showers. Northwesterlies, becoming gusty this afternoon. 18degC high, 11degC overnight.
Wellington Few showers developing this morning, then rain and possible thunderstorms tonight. Northwest, gale in exposed places from afternoon. 15degC high, 9degC overnight.
Christchurch High cloud, then showers this evening as strong northerlies turn northwest then southwest. 16degC high, 1degC overnight.
Dunedin Showers developing around midday then clearing evening. Gusty northwest turning southwest by evening. 13degC high, 3degCovernight.