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 130km/h through the Canterbury high country.

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 18C and 20C respectively.

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Conversely, temperatures have dropped below 0C 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.

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.

Northwesterly winds could reach 130km/h 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.

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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.

About the Marlborough Sounds, Wellington, Kāpiti, Horowhenua, Taranaki, Waitomo and Taumaranui thunderstorms could be severe late Tuesday bringing damaging wind gusts over 110 km/h, with potentially small tornadoes.

Tomorrow the front sweeps east across the North Island early in the morning bringing a moderate chance of heavy rain from Kāpiti northwards, and northwest gales early morning from Wellington to the central North Island high country and the ranges of Gisborne and the eastern Bay of Plenty.

Most areas in the North Island are in for a wet day tomorrow, particularly those facing west, including Taranaki and Auckland.

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.

Today's weather

Whangārei

Occasional showers, some possibly heavy. Northwesterlies becoming gusty this afternoon. 20C high, 12C overnight.

Auckland Occasional showers, some possibly heavy. Northwesterlies becoming gusty this afternoon. 18C high, 11C overnight.

Hamilton Occasional showers, some possibly heavy. Northwesterlies becoming gusty this afternoon. 17C high, 9C overnight.

Tauranga Occasional showers. Northwesterlies, becoming gusty this afternoon. 18C high, 11C overnight.

New Plymouth

Occasional showers, then rain from evening with thunderstorms. Northwesterlies strengthening this afternoon. 17C high, 9C overnight.

Napier Fine, some high cloud. Northwesterlies strengthening this evening. 20C high, 10C overnight.

Wellington

Few showers developing this morning, then rain and possible thunderstorms tonight. Northwest, gale in exposed places from afternoon. 15C high, 9C overnight.

Nelson​ Fine morning. Showers by evening, chance heavy and thundery. Northerlies strengthening. 16C high, 4C overnight.

Christchurch​ High cloud, then showers this evening as strong northerlies turn northwest then southwest. 16C high, 1C overnight.

Dunedin​ Showers developing around midday then clearing evening. Gusty northwest turning southwest by evening. 13C high, 3C overnight.