Inland Pilbara communities could be heading into uncharted territory as Severe Tropical Cyclone Ilsa looks set to rip through the region at sustained strength.
Key points:
- Cyclones normally weaken significantly as they move inland
- But Tropical Cyclone Ilsa will weaken much more slowly
- It is expected to put some inland communities at unprecedented risk
The latest track map from the Bureau of Meteorology shows Ilsa hitting the Pilbara coast late on Thursday as a Category 5 – the highest category there is — with gusts in excess of 250kph.
But unlike systems of the past, the cyclone is forecast to maintain intensity as it travels eastwards toward the Northern Territory border, remaining a strong cyclone for hundreds of kilometres.
The latest track map projects Ilsa to pass north of Marble Bar as a Category 4, directly over Telfer as a Category 3 and over the remote community of Kunawarritji as a Category 1 on Friday, before weakening to a tropical low as it continues its path inland.
‘Intensity’ not seen this far inland
Bureau of Meteorology senior meteorologist Jessica Lingard said cyclones usually weakened well before they reached that far inland.
“We have seen systems moving past Telfer that have brought an intense amount of flooding and there have been some strong winds that we have seen, especially with tropical cyclone Anika,” she said.
“But nothing to the intensity of a Category 3 system almost moving on top of the town.”
She said the inland town sites were not built to the same strength as those on the coast.
Category 3 cyclones have mean wind gusts up to 159kph, with the strongest gusts up to 224kph.
“Most inland sites are not used to seeing wind strength of this nature,” Ms Lingard said.
Australia’s wind ratings show Marble Bar is rated as “wind region B”, which is built for wind speeds up to 205kph.
Much of the eastern Pilbara, inland of Marble Bar, is classified as “wind region A”, which is the same as Perth.
Telfer is home to Newcrest’s gold and copper mine and has population of 657 people, according to the 2021 census.
Ms Lingard said the north side of the system was the stronger side of the storm.
“If the storm were to pass to the south of Telfer then it would be getting the north-westerly winds, which are stronger and therefore the damage could be much worse.”
But she said its speed would hopefully mean less damage.
“The quicker the system moves, the less amount of rainfall we’re going to see falling in one spot,” she said.
Similarities to TC George and TC Laurence
As Ilsa nears landfall, its path has become reminiscent of two other severe and destructive cyclones of the last two decades.
TC George and TC Laurence both crossed the coast in a very similar proximity and strength to the forecast for Ilsa.
Cyclone George, in March 2007, caused extensive damage to communities in the far north of Western Australia with three fatalities and 20 people injured.
Cyclone Laurence in December 2009, caused considerable damage to properties within its path, and killed 1,500 cattle.
But Ms Lingard said Ilsa was unlikely to follow the same script of destruction, with both systems tacking a more southerly track after landfall.
“So TC George crossed slightly closer to Port Hedland,” she said.
“And it then took a more southerly turn into the mine site areas of the Pilbara, down toward Newman and it did pass through an awful lot of mine sites.”
She said TC Ilsa was taking a more easterly turn, which would hopefully lead to less destruction.
“It’s [forecast track] actually moves through a fairly uninhabited area of WA,” she said.
“I’m likening it to a bit of a tropical cyclone alley that seems to have naturally developed, with a lack of infrastructure, lack of Aboriginal settlements and really a lack of anything through that area.
“So if the system is to cross anywhere, this is the place we want it to.”