On the night of April 10 this year, Auckland lost 40 per cent of its power network in just 15 minutes.
The storm was unexpected, and is still not regarded as a hurricane in the way other storms of similar ferocity are, when they strike elsewhere in the Pacific.
Executives from the power company Vector reported on the story to a meeting of the Planning Committee of Auckland Council today. CEO Simon Mackenzie revealed they now call the storm "Hurricane No Name".
Chief networks officer Andre Botha said that between 1pm and just before 9pm, evening winds were gusting at 100-125km/h, which is severe enough to cause damage, but they were confident the network was holding up well.
Then at 9pm the wind suddenly became twice as fierce, with gusts up to 215km/h.
"We lost 40 per cent of the network over a 15-minute window," said Botha.
"There were 4000 points of damage."
The storm, which lasted through the night and into the following day, was violent and unpredictable. At Muriwai, a tree came down right behind a service team, narrowly missing them and destroying all the repair work they had just done.
Hurricane No Name knocked out power to over 200,000 Auckland properties, and with many of them the damage on the property itself was too severe for power to be reconnected straight away. Some homes were without power for up to 11 days.
As has been earlier reported, the Insurance Council says more than 13,000 claims were made following the storm.
Botha told the council meeting that it is now engaged in a major exercise to strengthen the resilience of Auckland's power network, but the answers are not straightforward.
City growth means the company is "building new network capacity the size of Hamilton every 2.5 years".
Currently, 55 per cent of the network is underground, and all new lines go underground.
Botha said the cost to replace overhead power lines with underground lines in urban Auckland was $3.6 billion. The cost to do the same for the rural parts of the city was another $1.9 billion.
"Those costs don't include the other things that might typically be done with undergrounding the power lines, such as putting telephone cables underground at the same time."
In a separate statement, Simon Mackenzie said the cost of undergrounding the entire network "could potentially quadruple electricity bills for decades".
There are some problems with undergrounding. Mackenzie warned that it would mean a write down of assets, which posed "an economically difficult decision" for Vector.
And while lines underground are safer from storm damage, when damage does occur it is more expensive to repair. During the April storm, some uprooted trees brought up power lines with them.
Mackenzie suggested that Auckland needs to have a larger conversation about trees near power lines. Current regulations are that the "cut zone" should be 1.5 metres around the lines.
"In some jurisdictions the cut zone is 40 metres", he said.
Councillor Penny Hulse responded to that by saying she was "not going to use a rude word, but I think Aucklanders face a clusterdrama. We love our trees but do we love our cups of coffee even more?"
Vector has today released a discussion paper on resilience that calls for a "more holistic" approach. Vector believes Auckland cannot rely on undergrounding alone to prevent storm damage to the power network.
Andre Botha told the council meeting that new technologies are now starting to provide better options for resilience. Microgrids, for example, can help out-of-the-way communities like Kawakawa Bay, which is regularly affected by "climate-change-related weather events".
In urban areas, "smart poles" are now able to carry power lines above the tree line.
In his separate statement, Mackenzie said, "Globally there is a growing awareness and sharper focus on emerging technology to unlock the opportunities of shared resilience that lie ahead.
"Our paper calls for more discussion on how industry, government and consumers can work together to deliver the best possible outcomes for New Zealand," he said.