New Zealand faces an elevated risk from ex-tropical cyclones over the next six months, with Niwa flagging the potential for one to two of these destructive systems swinging our way. Photo / JMA
New Zealand faces an elevated risk from ex-tropical cyclones over the next six months, with Niwa flagging the potential for one to two of these destructive systems swinging our way. Photo / JMA
New Zealand faces an elevated risk from ex-tropical cyclones over the next six months, with Niwa flagging the potential for one to two of these destructive systems swinging our way.
Each season - usually around late summer - at least one ex-tropical cyclone veers within 550km of the country, packing gale-force winds and enough moisture to drive torrential rain.
While last year's outlook similarly forecast one to two systems amid the same tropical conditions forming now, yet none arrived here, Niwa meteorologist Ben Noll said there was a notable difference this season.
As with last year, La Nina conditions increasingly appeared to be developing in the tropical Pacific - and this could result in unusually warm ocean extending as far southward as the Coral Sea, an important "genesis region" for cyclones.
Noll said there were also indications that waters between this region and the northern Tasman Sea could also be running hotter than usual over the season.
"That can help sustain those systems as they track southward," he said.
"We saw a similar set-up to this last year, but a high pressure belt that was commonly over New Zealand during the period kept deflecting the systems off to the north.
"This year, based on some of the analogues we've picked out, that high pressure belt may be pushed far enough south at times to allow more of these cyclones to get closer to New Zealand.
"For that reason, we felt it prudent to acknowledge the elevated risk."
Across the wider southwest Pacific basin, Niwa was forecasting between nine and 12 named cyclones between November and April - a range also above normal.
There were higher chances of systems in and around the Coral Sea, especially between February and April, along with an elevated risk in the subtropics between Fiji and New Caledonia.
Fire chief Colin Eggers makes his way through floodwaters in Riwaka, Tasman District, after ex-tropical cyclone Gita hit in February 2018. Photo / Tim Cuff
The forecast picked the potential for at least three cyclones in the basin to reach category 3 status.
Meteorologists consider a "severe tropical cyclone" one that blasts as hard as 118km/h, and each season.
Only a few of those ever reach category 4 strength, where mean wind speeds reach more than 159 km/h, or higher.
Fewer still reached category 5 - with winds speeds of more than 200km/h - but some of these monsters had formed up in seasons with similar conditions to those forecast for 2021/22.
Vanuatu and New Caledonia generally experienced the greatest cyclone activity, with an average of two or three named systems passing close to land each year.
💨 2021-22 Tropical Cyclone Outlook 🌴
🌀 9 to 12 cyclones are predicted across the SW Pacific from Nov-Apr, which is near or slightly above normal
❗ New Zealand has an elevated risk (1-2 cyclones possible)
While there was little action on the immediate horizon, Noll said last season showed just how quickly systems could develop.
The Category 5 Yasa, which formed last December, killed four and caused hundreds of millions of dollars in damage in Fiji, proved the strongest tropical cyclone in the South Pacific since Winston in 2016, as well as the fourth most intense on record in the basin.
"These can come up fast, so anyone spending time in the waters between New Zealand and New Caledonia, Vanuatu or around Norfolk Island, will certainly want to take note."
Recent years have also highlighted the impact remnants of these systems can have here.
Over 2017-18, New Zealand was hit by ex-tropical cyclones Fehi and Gita, which struck within weeks of each other in February and caused tens of millions of damage to the South Island's West Coast.
Cyclone Hola, which formed a month later, nearly reached Category 5 strength as it bore down on Vanuatu and caused widespread havoc, killing one.
What was left of it later brought heavy rain and wind to northern North Island as it swung by our coast.
