Meanwhile the MetService has issued a severe wind warning for Auckland and Northland, with possible gusts up to 120km/h.
Severe weather watches have also been issued for the North Island down to Taupo and Taranaki, with strong winds and heavy rain expected overnight and into the morning.
Severe gale northeasterlies gusting 120 km/h in exposed parts of Northland should ease early morning, while Auckland can expect northeasterly gusts of 100 km/h until around dawn on Monday, the forecaster said.
A narrow band of rain moving over the upper North Island could produce localised downpours of 25-35mm/h, mostly in spots north of Whangarei, MetService said earlier this evening.
"Rainfall of this intensity can cause flash flooding, especially about low-lying areas such as streams, rivers or narrow valleys, and may also lead to slips," MetService said.
"Driving conditions will also be hazardous with surface flooding and poor visibility in heavy rain."
Northland has already taken a lashing from storm-force winds that barrelled across the top of the country. By this evening gusts of around 120 km/h were blasting Cape Reinga, with average wind speeds around 100km/h.
The potentially destructive gales descended on the Far North this morning, buffeting the region for 12 hours and sweeping down over the top half of the North Island.
Auckland was pelted with rain and strong winds this afternoon, after nearly week of sunshine. This evening's rain band is also set to move down the bringing more bad weather this evening, and could slide south to Auckland later tonight, Niwa said.
WeatherWatch.co.nz said the coastal Bay Of Plenty would also see gusty northeasterlies which would peak overnight, and coastal Taranaki would get strong northeasterlies.
Northland, Auckland and Waikato Civil Defence groups are warning people of the impending bad weather on social media, reminding them to tie down trampolines and take care driving.
MetService is warning the gusts of up to 120 km/h could topple trees and powerlines, and damage unsecured structures.
Driving is also expected to be hazardous, especially for high-sided vehicles and motorcycles.
A severe wind warning is in place for Auckland from this evening until about dawn on Monday.
In addition, the forecaster has issued a "severe rain watch" for Auckland tonight.
"There is a possibility that the rain could come close to warning criteria which, for example, would be something like 60mm in nine hours," MetService's Erick Brenstrum said.
"These gale-force winds, which could gust up to 100km/h, are ahead of a front which should be crossing over Auckland around midnight. That will bring north or north-easterly winds but those won't be so strong."
Brenstrum said most of the country had been enjoying four or five days of fine weather last week, with the exception of Fiordland which had seen heavy rain.
The oncoming poor weather would be followed by a southerly change, which would bring calmer weather late on Monday. This would result in colder weather in the south early in the week and in the north on Thursday or Friday, Brenstrum said.
While poor weather for much of the North Island was forecast for today, Christchurch and Dunedin were expected to be fine.
Much of the country was expected to be hit by either rain or scattered showers on Monday.
By Tuesday, Auckland was only expected to experience scattered showers, Hamilton would be cloudy and Wellington would be cloudy with the chance of showers late in the day.
The South Island is expected to be cloudy.
