Otago and Canterbury headwaters can also expect significant rainfall with 500mm possible about the divide and 280mm within 20km of the divide during tomorrow and Tuesday.
The cold front will slowly sweep over the South Island before stalling over the North Island about midweek.
In Auckland, weather consisting of cloudy periods and isolated showers can be expected before the front arrives and with it, rain and windy conditions.
"As [the front] stalls, it's going to bring more rain and shower activity across the North Island," MetService meteorologist Josh Griffin said.
"In Auckland ... there is some rain developing late Wednesday into Thursday and it'll kind of be cloudy and a bit showery for the Auckland area towards the end of the week."
However, the time has not yet come to pack away the shorts and t-shirts with New Zealand's long, hot summer set to linger.
Temperatures have remained consistently in the mid to high 20s for the upper North Island and in the low 20s for much of the rest of the country.
A high-pressure system brought settled weather to the country this month and despite the arrival of the cold front midweek, the weather will remain warm.
The continuing mostly settled, warm weather might be bringing smiles to many, but it was no anomaly.
"It seems to be nothing out of the ordinary for this time of year ... it's not going to be getting cold just yet," Griffin said.
WeatherWatch.co.nz says the combined rain bands will create a significant rain event with totals potentially exceeding 300 or 400mn in the next few days on the West Coast.
"While the West Coast, especially Fiordland and Westland, are used to big rainfall totals, the rain coming this week is above normal and could lead to slips, flooding and road closures and detours."
The heaviest rain would from around Hokitika southwards.
"It's unlikely much rain will fall over eastern areas like Canterbury, but some is possible especially closer to the ranges.
"For those needing rain in the North Island this front will weaken significantly as it moves northwards around late Wednesday and Thursday, but there may be some isolated downpours which bring relief."
Monday forecast:
Whangarei: Cloudy periods, chance shower. Northeasterlies. 24C High, 16C Low.
Auckland: Cloudy periods, chance morning shower. Northeasterlies. 24C, 17C.
Hamilton: Some morning cloud or fog, then fine. Chance afternoon shower. Light winds. 25C, 11C.
Tauranga: Mostly cloudy, a few morning shower. Northerlies. 23C, 17C.
Napier: Fine, apart from some morning cloud. Light winds and afternoon northeasterlies. 27C, 16C.
New Plymouth: Cloudy periods and the odd shower. Northerlies. 23C, 17C.
Wellington: Cloudy periods, and isolated showers in the north. Strong northerlies. 21C, 18C.
Nelson: Cloud increasing, chance shower from afternoon. Northerlies developing in the afternoon. 23C, 17C.
Christchurch: High cloud increasing. Northerlies. 28C, 17C.
Queenstown: Occasional rain. Westerly breezes. 21C, 15C.
Dunedin: Occasional rain. Northerlies. 23C, 19C.
Invercargill: Occasional rain. Northerlies. 23C, 15C.
