Tropical Cyclone Gita, seen here on February 18, 2018, via satellite, destroyed more than 170 homes in the Pacific and caused flooding across New Zealand. Image / JMA
Tropical Cyclone Gita, seen here on February 18, 2018, via satellite, destroyed more than 170 homes in the Pacific and caused flooding across New Zealand. Image / JMA
A new state-of-the-art model built by Kiwi and Australian scientists could give New Zealand and Pacific nations months' more warning of devastating tropical cyclones.
On average over the November-to-April season, about 10 tropical cyclones form in the Southwest Pacific basin - some reaching category 4 strength, and packing wind speeds of more than 160km/h.
Vanuatu and New Caledonia typically bear the brunt of them – an average two or three pass close to the land there annually – and since 1950, these systems have killed an estimated 1500 people.
While an average of just one sweeps within 550km of New Zealand each year, usually around February and March, the impact can be catastrophic – as a flood that put Edgecumbe underwater in 2017 showed.
Around October, agencies issue a seasonal outlook, giving a general prediction of the number of cyclones that can be expected, and roughly where in the basin.
"Tropical cyclones are erratic, spatially and temporally, and every season is different," explained Dr Andrew Magee of Australia's University of Newcastle, who worked alongside Niwa scientists on the new model.
"This makes it difficult for island nations and territories to prepare in the weeks and months before the official start of the tropical cyclone season."
The new model had the potential to sharpen that forecast by generating predictions of cyclone numbers for individual countries – and four months ahead of the season's start.
The researchers had earlier explored how complex interactions between the ocean and atmosphere influence when and where tropical cyclones form and move.
With data being updated each month, the model could factor in the added influence of shifts in El Niño-Southern Oscillation.
For governments, aid agencies and the public, having an earlier, more detailed heads-up could be life saving.
"The provision of accurate and timely seasonal tropical cyclone outlooks are essential for informed decision making, and if we can just make small incremental steps in reducing disaster risk and informing the population of the risks associated with the coming cyclone season, then it has the potential to save lives," Magee said.
The flooding of Edgecumbe in April 2017, amid ex-Tropical Cyclone Debbie, highlighted the devastating impact that even remnants of cyclone systems can have. Photo / Whakatane Beacon
"Rising sea levels and changes to tropical cyclone related exposure and vulnerability will amplify future tropical cyclone related impacts for Pacific Island nations and territories.
"Our new outlook plays an important role in building a more resilient future for Pacific Island communities."
Niwa scientist Dr Drew Lorrey saw obvious benefits for New Zealand itself, which typically had some form of interaction with a tropical cyclone in nine out of every 10 years.
"I think [the model] has got a couple of really useful applications that we previously didn't have – the first of which is getting a heads-up about interactions that northern New Zealand might experience," he said.
"The other thing is that, because of our connection to the Pacific, and the aid we help co-ordinate in response to severe tropical cycles, having an advance warning system to plan with at an inter-governmental level is really useful and important."
Lorrey said the model had come alongside big leaps in short-term and medium-term forecasting over recent times, enabling meteorologists to get initial signals of a system's impact up to 14 days out.
"This is just one more tool that can provide us with a bit of an early view."
The new model will be used by Niwa to complement its island climate updates, and guidance will also be made freely available on the Tropical Cyclone Outlook for the Southwest Pacific (TCO-SP) website.
