The rain should start to ease in Auckland on Sunday morning. The East Cape was also in for a significant downpour over the next week or so.
"It's looking like it'll go on for another week or even two, which is not what you'd expect for spring. This is almost the opposite of what you'd expect for this time of year which is westerly winds and rapid changes in weather," Adams said.
The driest parts of the country would likely be the West Coast, Fiordland Southland, the Manawatu and Kapiti Coast.
Wellington has been experiencing non-stop southerly winds for the past week or so - something that has only happened 14 times in the last 56 years, Adams said.
The capital was getting on average just 2.6 hours of sunlight per day this September, compared to the historical September average of 5.7 hours.
"It's looking like it could be one of the lowest sunshine hours for Wellington for quite some time," Adams said.
"It's not going to be a very nice week for a lot of places, although that's a pretty subjective thing. And it could go for a lot longer than a week, although a lot can change in that space of time."