Heavy rain and gale force winds are expected to hit southern and central parts of the country this week causing rivers to rise rapidly, surface flooding, slips and hazardous driving conditions.
Significant changes in the weather are being forecast for this week, with severe weather warnings and watches issued for some regions.
For the South Island, heavy rain is falling in the west of the South Island and parts of State Highway 6 near Haast have already been flooded, while northwest gales are forecast in the east.
"A change is coming for many this week, as a cold front moves over the South Island and lower North Island," MetService meteorologist Rob Kerr said.
Warm, moist northwesterlies ahead of the front are set to bring "heavy rain and gale force winds to southern and central parts of the country during the next few days".
Significant heavy rainfall is expected in Westland south of Otira, Fiordland, and the Canterbury and Otago headwaters today and tomorrow.
Milford Sound has recorded more than 200 millimetres of rainfall so far.
Up to 700mm is forecast to fall on Fiordland and West Coast ranges south of Otira until Tuesday.
There is high confidence that rainfall accumulations will exceed warning criteria in these areas.
There is a warning that the heavy rain may cause streams and rivers to rise rapidly, including surface flooding and slips, and driving conditions may be hazardous.
There is some rain for Buller and Westland from Otira northwards on Tuesday, then increasing on Wednesday.
For Mount Taranaki and the Tararua Range there is low confidence that a heavy rain warning will be required on Wednesday.
Gusty winds warning
A weather watch is in place as northwest gales could become severe, starting in Southland and Fiordland Monday evening, then all of Otago and Canterbury on Tuesday.
In the Canterbury high country, gusts of upto 130 km/h are expected in exposed places, which could damage trees, powerlines and unsecured structures.
In Wairarapa, Wellington and Marlborough severe gale force is forecast in exposed places at times from Tuesday afternoon until Wednesday afternoon.
The weak front is set to stalls over northern New Zealand on Thursday, while a ridge of high pressure builds over the remainder of the country.
"This is both a significant event, and a big change from current conditions ... with updates to current severe weather warnings and watches likely as the system approaches, and further severe weather warnings and/or watches possible as it moves northwards during the week," Mr Kerr said.