Mother Nature has sent a reminder that winter is closing in after heavy downpours left Auckland ranked as the country's wettest place this morning and temperatures in the South Island plummeted below zero.

Parts of the city were hit by surface flooding as rainfalls continued into this morning and Orewa, Warkworth and northern Auckland were hit hardest.

Between 40mm and 70mm of rain fell on the northern suburbs, while between 20mm and 30mm fell close to the city centre, MetService meteorologist Stephen Glassey said.

Freezing temperatures have again hit the South Island after Mt Hutt in Canterbury was earlier blanketed in snow in February. Photo / Sarah Hutchins
Freezing temperatures have again hit the South Island after Mt Hutt in Canterbury was earlier blanketed in snow in February. Photo / Sarah Hutchins

The bulk of the rain had now eased, but there was still "the chance of the odd heavy shower this afternoon" as the city warmed to its high of 20C, Glassey said.

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"We expect a much improved day tomorrow with just a few showers and long dry breaks and a top of 20C."

Elsewhere, temperatures took a dive in the South Island overnight with Omarama in southern Canterbury being the country's coldest place as it fell to -4.8C.

Tekapo in the Mackenzie Basin was the next coldest town, hitting -4C, while Dunedin and Invercargill airports both dropped to -1.5C.

Glassey said the South Island could expect frosts this time of year, but temperatures were still below average.

Frosts also hit parts of Central Otago and Southland.

Ironically, the freezing temperatures were being caused by clear skies and light winds, which create wonderful, sunny blue skies during the day but then send the mercury plummeting at night, Glassey said.

A heavy rain warning was now in place for eastern Marlborough and the Kaikoura coast in the north of the South Island, where up to 150mm could fall from 7pm tonight into the early hours of Sunday.

There was a risk of thunderstorms also hitting Northland, Wellington's eastern hills and Hawke's Bay.

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Tauranga and Hamilton can expect tops today of 21C and 20C, while Wellington can expect a cloudy and rainy high of 12C.

Christchurch and Dunedin are set for highs of 13C and 12C.

Saturday forecast

Whangarei:

A few showers, some could be heavy. Southeasterlies. 20C High, 11C Low.

Auckland: Chance of odd heavy shower. 20C, 11C.

Hamilton: Partly cloudy. Chance of a shower. Southeasterlies. 20C, 6C.

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Tauranga: Partly cloudy. Chance of a shower. Southeasterlies. 21C, 10C.

Napier: Cloudy and showery. Southwesterlies. 16C, 8C.

New Plymouth: Partly cloudy. Chance of a shower. Strong gusty southeasterlies. 17C, 8C.

Wellington: Cloudy, rain developing by evening, with possibly heavy falls. Strong cold southerlies. 12C, 9C.

Nelson: Becoming cloudy. Possible evening showers. Light winds. 17C, 7C.

Christchurch: Occasional showers. Southerlies. 13C, 6C.

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Queenstown: Fine. Light winds. 15C, 5C.

Dunedin: Fine. Light winds. 12C, 7C.

Invercargill: Fine. Easterly breezes developing this afternoon. 14C, 0C.