A slew of heavy rain and strong wind alerts are currently in place across the North Island and top of the South Island.
Heavy rain is expected to start falling in the centre of the country for 40 hours starting at 8pm.
Up to 300mm of rain could be dumped in central New Zealand depending on how fast the cyclone passes over.
Many regions could expect to be walloped by cyclonic gale-force winds, including the top and bottom of the North Island.
Forecasters are warning those living in the lower North Island and upper South Island should prepare for heavy rain, slips and possible flooding. Strong winds and dangerous coastal conditions are also possible elsewhere.
A tongue of tropical moisture had already brought wet and humid conditions to much of New Zealand this week. A state of emergency is in force in Buller where a deluge of rain forced people to be evacuated from homes yesterday.
WeatherWatch.co.nz said the storm was expected to retain Category 2 strength as it dive-bombs into New Zealand this weekend from the north.
"While it will have a lot of intense energy as it moves southwards over the Tasman Sea it is expected to unravel over New Zealand - but that means it will dump a lot of rain here and as it 'falls apart' it will also bring areas of damaging gales into both main islands," said the forecaster.
Today, MetService said the position of the low-pressure centre would become less important in the coming days, with severe weather forecast for many areas of New Zealand not in direct line of the central pressure.
On the other hand, the wind and swell would peak as the low-pressure centre drew close this weekend.
Weatherwatch.co.nz said heavy rain could even start falling this afternoon about the Taranaki region before setting in over the lower North Island tonight.
The heavy rain would affect the lower North Island and top of the South Island across the weekend.
The strongest winds would likely be during Sunday as the main low crosses over.
The government forecaster was due to take over the official warnings for the cyclone today as the system crosses 25° South.
