These places could see a drop down to the mid teens today. Christchurch was in for a high of 16C and Dunedin just 13C.
The rain and cool change would reach the lower South Island by this evening, bringing cold southerlies to Wellington.
On Friday the front would move further north but weaken and become showery as it reached Bay of Plenty, Auckland and Northland.
The South Island was in for much of the same, with lots of fine breaks and just some isolated showers.
On Saturday a weak low was forecast to come out of the north Tasman Sea and approach the North Island.
There was likely to be rain over much of the North Island and northern South Island during Saturday and Sunday, and about the eastern Bay of Plenty ranges potentially heavy rain on Sunday and early Monday.
"Generally the weekend is getting pretty unsettled," Matheson said.
"Showers will spread over western areas Saturday with outbreaks of rain in the North Island and upper South Island."
On the plus side, the system is approaching from the north and will bring with it warm northerlies, pushing the cool southerlies away.
Sunday was looking like a wet day for the Bay of Plenty, and parts of Auckland and the Coromandel could see a heavy shower or two during the morning.
As the low moved out to the east of the country on Monday, a strong southwest flow should spread over New Zealand.
Today's weather
Whangārei
Long fine spells, then clouding over evening. Light winds. 22C high, 12C overnight.
Auckland
Long fine spells. Clouding over in the evening. Westerly breezes. 20C high, 14C overnight.
Hamilton
Mostly cloudy with light showers, but fine spells in the afternoon. Westerly breezes. 19C high, 11C overnight.
Tauranga
Fine apart from some morning and evening cloud. Westerly breezes. 20C high, 13C overnight.
New Plymouth Mostly cloudy with a few showers, then evening rain. Northwesterly winds. 18C high, 9C overnight.
Napier A fine day with sea breezes. High cloud and northwesterlies in the evening, then a period of rain overnight with a southerly change. 23C high, 12C overnight.
Whanganui Cloudy periods. Rain from late evening. Northwesterlies changing southerly overnight. 20C high, 10C overnight.
Wellington Cloudy with northwesterlies. Rain from evening with a cold strong southerly. 17C high, 9C overnight.
Nelson Mostly cloudy. A period of rain late afternoon or early evening. Northerlies dying out in the evening. 18C high, 10C overnight.
Christchurch Rain in the developing morning with a cold southerly change. Rain clearing in the evening as winds die out. 16C high, 5C overnight.
Dunedin Morning rain, then one or two showers until evening. Cold southerlies dying out in the evening. 13C high, 7C overnight.
