The next low could possibly bring hurricane-force winds in exposed areas around Manukau Heads.
"As far as Auckland is concerned the worst for today is over, however tomorrow we get the back-end of this system coming through.
"These systems are so big they're covering the whole country. It's not just for one or two regions, it's pretty much for the whole country."
The series of lows were a typical spring pattern - fitting for the first day of the season today, Mr Duncan said.
The rain should ease for most by Sunday or Monday, when a cold snap could be on the cards.
"It's not just one clear-cut weather system, there's two or three. They're surrounding each other and egging each other on to bring more rain.
"After these systems go by we tend to get a cold blast of air. I wouldn't be surprised if we got a cold snap then back to the warmer and drier weather."
Auckland has clocked gales gusting up to 90km/h so far with about 55mm of rain recorded over the past 24 hours - almost double yesterday's rainfall figures.
Some of the heaviest falls saw 20mm accumulate in one hour.
MetService meteorologist Hannah Moes said the stormy weather was easing for Auckland but would batter other centres today.
MetService has issued a severe weather warning for heavy rain in the Bay of Plenty, Waikato and Nelson as well as strong wind warnings in Nelson, Buller and Westland.
This afternoon might be the calmest period in Auckland before another bout of stormy weather moves through on Wednesday and Friday, she said.
"We're expecting Auckland will see quite a significant clearance behind that front. By midday most of the region will be out of rain," she said.
"But another front passes through late tomorrow...then on Friday another low approaches the country which will bring more rain."
Today's forecast:
Whangarei: Heavy rain, fine spells. High 19C Low
Auckland: Heavy rain with strong northeasterly until noon then fine. High 17C
Hamilton: Rain until midday northwesterly change, then fine spells. High 16C
Tauranga: Heavy rain, strong northeasterly until afternoon. High 17C
Wellington: Rain easing to showers. Gusty southeasterly then strong northerly. High 13C
Christchurch: Drizzle turning to rain. Easterlies. High 10C
Dunedin: Drizzle, turning to rain. High 9C
Tomorrow's forecast:
Whangarei: Cloudy periods, chance of showers. High 19C
Auckland: Occasional showers, more frequent in evening. High 18C
Hamilton: Showers turning to rain. High 17C
Tauranga: Fine spells, odd shower. Rain afternoon. High 17C
Wellington: Occasional showers, northerlies dying out. High 14C
Christchurch: Periods of rain, Southwesterlies developing. High 12C.
(Source: MetService)