Experts are urging the public not to get caught up in category numbers after Tropical Cyclone Vaianu was downgraded from a category three to a category two storm.

Chester Lampkin, meteorologist with Earth Sciences New Zealand, told Richard Martin on The Front Page that the incoming weather system remains a genuine threat despite the downgrade.

He said cyclone categories represent the scientific intensity of a storm, but they’re not a reliable indication of impact on people and property.

“Essentially, they don’t have much meaning when it comes to the amount of damage that can be done,” Lampkin said.

“It’s great for being able to put things in nice fit categories for scientific purposes, but when it comes to the human element, we know that we are impacted in different ways that can’t always be put into a number category.”

Lampkin said the common misconception that a lower category means less damage is the reason meteorologists try to focus on communicating the potential impact of a storm independent of how it’s categorised.

“Category five means nothing if it makes no landfall anywhere, right? But a category one – you’ll remember that storm if it blew your house down or if it destroys your neighbourhood, or if you know someone who unfortunately loses their life in that storm,” Lampkin said.

An image of the wind forecast for 6am, Sunday April 12. Image / Niwa

Speaking specifically about Cyclone Vaianu, he said it “could be one of the worst storms we’ve seen in years. It could also be a storm that no one will remember in a year”.

Lampkin said the MetService issuing a severe weather watch covering the entire North Island unusually far in advance was a clear signal.

“I think that points to how serious this situation could be as far as wind impacts, and I know they’ve put out some heavy rain watches as well. So, certainly I would say, top two serious situations of the summer/autumn so far.”

Adding to the risk profile are weather patterns before the cyclone makes landfall. 

“We’ve had some heavy rainfall over the last week, so the soil and the ground is a bit saturated. It’s a bit primed. We’ve had a lot of rain over the last few weeks,” Lampkin said.

“As a result of that, the ground is not going to be able to hold as much water, so more than likely flooding slips will be a concern.”

Lampkin highlighted the east to southeasterly wind direction associated with this weather system as a further complicating factor.

“That’s an unusual wind direction for New Zealand; the trees are more used to westerlies. So, I think soggy ground, trees that are getting hit with strong gusts from an unusual direction – that could lead to a lot more trees falling.”

Lampkin said this combination of factors increases the likelihood of slips and widespread power cuts that could last between hours and days.

“What people need to know is that this is going to be a strong, generally impactful storm.”

Listen to the full episode to hear more on:

• What you should do to prepare for the storm
• Which areas of the North Island are likely to be most impacted
• How the accuracy of weather forecasts is improving

The Front Page is a daily news podcast from the New Zealand Herald, available to listen to every weekday from 5pm.

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