Auckland is set to experience one of the wettest 48-hour periods the city has had this year.
Weatherwatch.co.nz analyst Philip Duncan said there weren't many parts of the country that often received set-in rain for more than 24 hours.
Fiordland and the West Coast were no strangers to days of relentless rain but further north, rain tended to move through much faster.
The Southern Alps on the West Coast blocked the rain clouds but in Auckland, the city was surrounded by separate bodies of water, the Tasman Sea and the Pacific Ocean, Duncan said.
"With no tall blocking ranges rain clouds tend to pass through quickly, which is why the almost 24 hours of rain in our largest city is unusual - and why more rain for the next 12 hours or so will make this one of the wettest 48-hour periods the city has had this year as far as total hours with precipitation.
"There is one main difference between Auckland's set-in rain and what the West Coast gets - today the rain is fairly patchy and light, not at the levels we see further south."
He said he couldn't rule out "a few drizzly/dry spells today" but heavier downpours were coming in before finally easing overnight.
The MetService severe weather watch for heavy rain and strong winds over the upper North Island until tomorrow morning remains in place.
A deep low is approaching from the north Tasman Sea today. It is expected to cross New Zealand tonight and tomorrow, bringing significant rain and strong winds to the North Island.
Rain or showers are forecast to continue through to Sunday for Auckland and Hamilton, while Wellington can expect a clearance on Saturday and a fine Sunday.
Tomorrow - Showers easing for a time, 18C
Saturday - Showers clearing in afternoon,15C
Tomorrow - Showers easing for a time,17C
Saturday - Showers easing in the morning, 14C
Tomorrow - Rain easing in the morning, 13C
Saturday - Showers clearing in the afternoon,13C
Tomorrow - Morning fog, rain developing, 11C
Saturday - Rain clearing in the afternoon, 13C
Tomorrow - Drizzle turns to rain, 11C
Saturday - Rain clearing in the morning, 13C