Drivers have been warned to stay off the roads, with floods, slips, wind, snow and icy surfaces among possible hazards.
Flooding, downed powerlines and trees and upturned trampolines are all expected to greet residents tomorrow morning in the storm's wake.
MetService meteorologist Larissa Marintchenko said the storm was affecting the South Island with heavy falls in Fjordland and snow in high places in central Otago. Strong winds had hit Westport, where the strongest gust measured was 90kmh.
In Wellington gusts around 100km/h had been measured in Kilburne and 80km/h at the airport.
Rainfall is heaviest west of the Southern Alps, with Hokitika receiving 46.8mm in the past six hours and the Haast Pass getting 29.2mm. Heavy falls are expected to continue throughout the night, Marintchenko said.
The rain will be welcomed in the South Island, although Niwa has said it won't be enough to alleviate the long-term dryness in the region.
"The North Island will probably start to be affected after midnight," Marintchenko said.
"We expect some thunderstorms but only in Northland - there's the possibility of isolated thunderstorms and localised downpours in the early morning hours."
While the south is set to clear up tomorrow morning, the bad weather would come later further north, the MetService said.
The storm will be relatively mild when it arrives in Auckland but a brief burst of heavy rain is expected in time for the morning commute. A severe weather watch is in place for Auckland north through till 11am tomorrow, with rainfall intensity possibly reaching up to 35mm per hour.
Gales are also expected but nowhere near the severity forecast elsewhere.
In typical spring fashion, once the worst of the rain's over it's expected to clear the upper North Island, and the day should end with sunshine.
In the south snow is expected to fall as low as 300m in Fiordland overnight, while heavy rain warnings are in force for Westland, Fiordland, the headwaters of Canterbury and Otago Rivers and lakes.
Strong winds are also expected in Canterbury, Marlborough, Wellington, south Wairarapa, Horowhenua-Kapiti Coast, Manawatu, Whanganui and Taranaki south of the mountain.
Heavy rain may have caused streams and rivers to rise rapidly overnight in the south, and roads may be icy tomorrow morning. Surface flooding and slips are also possible and driving conditions may be hazardous.
TOMORROW'S FORECAST
WHANGAREI
Heavy rain clearing afternoon, gusty northerlies ease. High 21C, Overnight 10C
AUCKLAND
Heavy rain clearing late morning, gusty northerlies ease. High 19C, Overnight 12C
TAURANGA
Rain clearing afternoon, strong northerlies. High 20C, Overnight 9C
HAMILTON
Heavy rain clearing morning, strong winds. High 19C, Overnight 6C
NAPIER
Morning rain, then fine. Strong northerlies ease to westerly. High 23C, Overnight 9C
WELLINGTON
Heavy rain clearing 7am to fine. Gusts to 140km/h, easing morning. High 17C, Overnight 9C
