MetService is warning that significant amounts of rain could fall in Northland, northern Auckland, and the Coromandel Peninsula on Thursday and Friday, as well as for the Bay of Plenty and Tairawhiti to the north of Ruatoria on Friday.
A tropically charged low-pressure system sitting over the Tasman Sea is pushing a front across the country, MetService reports.
In previous heavy rainfall events that devastated regions, the front stalled in one area for a long time. MetService said this front will move quickly southeastward and will have moved away from the country by noon on Friday.
Forecasting agency Niwa said the worst of the wet weather is expected to hit Northland from about sunset to about midnight on Thursday, Auckland a few hours either side of Thursday midnight and Waikato from after midnight to about sunrise.
However, even during these shorter downpours, flooding and slips are possible as the weather is tropically charged and can create heavy deluges with thunderstorms.
A heavy rain watch is in place on Thursday night for Northland, Auckland, Coromandel Peninsula, and Bay of Plenty including Rotorua.
Strong winds will accompany the low-pressure system and there is a moderate risk of severe northeast gales in some regions of Northland, where a watch is in effect, Auckland, Coromandel, Waikato and Waitomo on Friday.
From Friday at 7am, Gisborne will be placed under a heavy rain warning, where thunderstorms and localised downpours are possible, with peak rates of 15 to 25 mm/h, or possibly more. A strong wind watch is also in place.
MetServise said a low over the Tasman Sea has already begun to affect Fiordland, Westland, Otago and Southland, causing snow to fall 800 metres inland. Orange rain warnings remain in place for Westland and are expected to extend until 6pm on Thursday.
More rain, strong gusts and massive swells will continue on Saturday as the low-pressure system tracks across the central North Island, bringing another round of rain or showers to most regions.
“A period of westerly gales will also affect northern parts of the country on Saturday as the low moves eastwards across the central North Island,” MetService meteorologist Peter Little said.
“The gusty westerly winds and already sodden soil means people are advised to be prepared for power outages due to falling trees disrupting power lines
“Rain or showers are forecast for most places on Saturday, with the west of the North Island and Tasman region likely to be the wettest places.”