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'Keep an eye on this one': Tropical storm looms in marine heatwave

Jamie Morton,
Publish Date
Wed, 17 Jan 2024, 12:35PM

'Keep an eye on this one': Tropical storm looms in marine heatwave

Jamie Morton,
Publish Date
Wed, 17 Jan 2024, 12:35PM

The southwest Pacific’s first tropical cyclone of 2024 could form within days – but meteorologists say there’s no sign yet of any risk to New Zealand. 

Forecasters are closely tracking potential for a tropical low over the Coral Sea to form into a cyclone system, with Australia’s Bureau of Meteorology currently giving a “high” chance (or 55 per cent) of it reaching cyclone strength by early next week. 

MetService’s latest outlook picked a moderate risk (20 to 50 per cent) of a system developing in the area, between Queensland’s northeast coast and New Caledonia, from Saturday. 

“We’ve been very lucky through the Christmas period, with it being a relatively settled time in terms of tropical cyclones, but sadly, things are about to get a bit more active up through the Coral Sea,” MetService forecaster John Law said. 

“It is an area of concern, and for us here in New Zealand, it’s looking like the second half of the month is going to be a different story to that first half.” 

Whether a system ultimately pushed south into our neighbourhood as an ex-tropical cyclone remained to be seen, “but it’s definitely a situation to be aware of, especially island groupings around that way”. 

Niwa meteorologist Ben Noll said that, among other favourable conditions for cyclone development over coming weeks, surface temperatures in the Coral Sea were running warmer than average. 

“Basically, west of New Caledonia, extending all the way to the coast of Queensland, we’re seeing moderate to strong marine heatwave conditions. 

“At this point, the heatwave also extends southward into the northern Tasman Sea, and also encompasses the North Island’s coastal waters, along with the top of the South Island – so it’s pretty widespread.” 

This ocean warmth was contributing to summer temperatures in New Zealand – including uncomfortably hot nights – despite earlier expectations that it wouldn’t be such a big factor here amid this season’s El Nino. 

Up in the Coral Sea, meanwhile, the marine heatwave could increase the potential for a formed cyclone system to intensify, while contributing more moisture. 

“I’d agree it’s too early to say what we can expect with this one,” Noll said of its implications for New Zealand. 

“But we do look to be going into what I’d describe as an unsettled pattern in the Tasman Sea, around the same time this tropical cyclone may form, and what that can do is potentially draw moisture at some point from the system.” 

Warmer seas happened to help fuel last month’s disastrous Jasper - which reached Category 4 strength and may have been Australia’s wettest tropical cyclone on record – and also last February’s Gabrielle. 

While the New Zealand region has received remnants of faded tropical cyclones so far this season, it’s yet to receive an unwelcome visit from an ex-tropical system, as occurred multiple times last season. 

Niwa has already forecast an elevated risk across large areas of the West Pacific, but picked a lower threat for New Zealand, with a subtropical ridge of high pressure above the country likely to prevent big rainmakers from travelling here with the relentless frequency of last summer. 

This map shows tropical cyclone risk for the 2023-24 season. Source / NiwaThis map shows tropical cyclone risk for the 2023-24 season. Source / Niwa 

Noll added a globe-circling pulse of rain and thunderstorms called the Madden-Julian Oscillation (MJO) could again prove a cyclone-building factor as it passed through the region next month. 

“That’s happening in pretty much the same region, which means this tropical cyclone may prove the first in a string of potential ones over the next four to six weeks.” 

Jamie Morton is a specialist in science and environmental reporting. He joined the Herald in 2011 and writes about everything from conservation and climate change to natural hazards and new technology. 

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