One weather forecaster is scratching his head today after Auckland was battered by a fierce storm that seemingly few people expected to have the force of a Category 2 cyclone.

"I am going to be asking lots of questions today about what we could have done better, because we didn't see that there would be lots of trees down and half the city without power this morning," WeatherWatch.co.nz head forecaster Philip Duncan said.

"It was a notch higher than what we were expecting," he said.

"It was a unique set-up yesterday. The whole system across New Zealand had quite a few moving parts and the low that caused the damaging winds to Auckland was forecast to actually bring gales into the city.

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"We put out warnings at 2pm yesterday to say specifically power cuts and trees would be down, but in saying that it was still worse than what was forecast."

He said one reason Auckland got hit so badly was because the area of gales wasn't very big, but it came directly through the city.

"Auckland was a particular wind tunnel for this so it really hit Auckland. Further north and south it wasn't quite as intense.

"It was a combination of a low deepening over the North Island, a southerly that was coming into the Auckland area and the centre of this deepening low making landfall in South Auckland at the same time as that southerly kicking in. So there was quite a lot going on at the time that it was all moving through.

"When you looked at a map of New Zealand, the area that had damaging gales really was quite small. It just hit our largest city."

But New Zealand's official weather warning outlet Metservice said it stood by its watches and said it couldn't have done anything more to warn New Zealanders.

Storm damage in Auckland. A woman was trapped in her car in Kingsland New North Road. Photo / Dean Purcell
Storm damage in Auckland. A woman was trapped in her car in Kingsland New North Road. Photo / Dean Purcell

"We had weather warnings out for a considerable period of time and before it was a warning, it was in the severe weather outlook," MetService meteorologist Tom Adams said.

"We had social media, press releases and radio interviews, so every base was covered.

"Apart from going around knocking door to door, there is not much more we could have done."

He said severe weather warnings for Auckland had widespread gusts of 120km/h.

"There was one gust at Manukau Heads that was significantly more than that, 213km/h, but when we put a warning out it was for widespread gusts and you can't just say the one worst observation is going to happen over the whole of Auckland."

Adams said people may have been caught out by a low yesterday afternoon that might have been seen as the major weather event.

"A line of thunderstorms came through in the afternoon that brought strong gusty winds with them, then as they moved away to the east there would have been a slight drop in winds before they picked up again in the evening.

"It is possible people got things confused and thought it was over, but warnings specifically said Tuesday evening."

He said the storm illustrated the importance of checking warnings and watches.

Niwa is also rejecting criticism that no one was warned the storm would be so severe.

Principal scientist Chris Brandolino says Niwa forecast the storm would be damaging - as early as Monday they were talking about the impact of destructive wind gusts on traditional and social media.

Brandolino says maybe people didn't hear or didn't take notice.