Severe gales and heavy downpours chased by bitter-cold southerly winds are likely to upset everyone except snow-deprived skifield operators this weekend.

A complex low pressure system is expected to bring wet, unsettled weather to most of New Zealand today, before a southerly blast starts travelling northward up the country tomorrow, MetService forecaster Matthew Ford said.

Heavy rainfall warnings have been issued for Nelson and the Bay of Plenty with both regions forecast to be pelted with up to 140mm and midday downpours of 20mm per hour.

In Auckland, storm-swollen tides on the Manukau and Waitemata Harbours are expected to be unusually high throughout the weekend and drivers were urged to take care travelling on city motorways.

NZ Transport Agency contractors would monitor conditions and divert traffic if sections of the motorway network had to be closed because of safety risks, Auckland state highways manager Tommy Parker said.

The worst-hit area was likely to be the highway and adjoining cycleway on the Northwestern Motorway, between the Patiki Rd interchange and the Rosebank Rd bridges.

"When the tides peak, the cycleway in this area will definitely be under water, and we are asking cyclists to try to avoid using it 1 hours either side of high tide."

Gales forecast to hit Taranaki, Golden Bay, Buller and North Westland were expected to peak this morning at gusts of up to 110km/h, causing a hazard for unsecured property

WeatherWatch analyst Philip Duncan said the rain would likely mean more weekend sport being cancelled today.

A cold southerly flow is due to develop over the South Island tomorrow, before blowing on to the North Island on Monday morning.

Skifield operators hoped the system would blast away a high that has been keeping away snowfalls.

Mt Ruapehu spokesman Mike Smith hoped this system would "open the Antarctic fridge door" and deliver sustained snowfalls ahead of Turoa skifield's scheduled opening next Saturday.

A spokesman for Mt Hutt skifield, which was supposed to have opened on June 11, said lower temperatures would help more man-made snow.