Tropical cyclone Ilsa has been downgraded to a category-three cyclone as it moves southeast through Western Australia. The storm first made landfall as a category-five cyclone, passing near Port Hedland around midnight.
Ilsa smashed into the largely uninhabited Pilbara region (the country’s most cyclone-prone region) at record-breaking speeds. It has delivered Australia’s highest ten-minute sustained wind speed record at landfall: about 218 kilometres per hour. The previous record of 194km per hour came from tropical cyclone George in 2007.
So, does this new speed make Ilsa a particularly menacing disaster? The science of reporting on cyclone wind speeds is highly complex – and it can be easy to misconstrue the figures without some context.
As Ilsa continues to move inland, it looks likely the storm will be further downgraded before it passes into the Northern Territory – and potentially over Alice Springs – later today and tomorrow.
Ilsa made landfall about 100km north of Port Hedland, which hosts the world’s largest export site for iron ore. But a red alert prompted most vessels to be moved farther west in advance, so it only caused minor destruction.
Analysis by James Knight at Aon’s Reinsurance Solutions expects in general it will cause only minor damage due to the remoteness of where it has hit.
Apart from the ten-minute sustained record mentioned above, Ilsa had a one-minute sustained record of 240km per hour, and a three-second sustained record of 295km per hour.
It’s usually the latter, more intense gusts, that cause the most damage in tropical cyclone events. When it comes to making potential damage assessment for insurance purposes, firms will often model damage associated with a three-second sustained wind speed.
But there are several challenges that come with recording and making predictions about cyclone wind speeds.
The Bureau of Meteorology maintains a national wind recording database, which uses instruments called anemometers. These measure wind speeds at locations across the country, and are often placed in flat areas, such as near airports.
Their specific placement is very important. That’s because wind can change form as it moves over and through certain types of terrain.
Generally, when we report wind speed we’re referring to atmospheric wind gust, or wind speeds at least ten metres off the ground, which we also call “open terrain” wind speed.
However, wind passing closer to the ground, where the topography varies, will often be higher than winds passing directly above. Wind will speed up, for instance, if it’s squeezed between two hills.
We know from post-cyclone damage surveys that wind speeds can vary significantly from one side of a hill to another. Therefore, aspect and slope are very important.
As far as disaster modelling goes, this is no small issue as it can skew recordings. It is quite possible there would have been wind gusts from Ilsa that exceeded what has been reported so far.
Australia lacks a sufficiently dense network of anemometers set up for long-term testing. We need a national network that is quality controlled with better spatial coverage, if we want to gain more valuable insight into the frequency and intensity of extreme cyclone wind speeds over time.
The equipment we have, although it’s designed to withstand extreme conditions, can also get knocked around and thrown offline – introducing data gaps in the time series.
Accurate and consistent data points are crucial if we want to record and predict the kinds of extreme winds we might experience from future tropical cyclones. And while the efforts of independent storm chasers and university groups do go some way, taking measurements from different sources can introduce a lot of uncertainty in the overall process.
Since 1975, there have been 48 category-five tropical cyclones to hit Australia – an average of about one per year. So while Ilsa sets a new record for the strongest sustained wind gust at landfall, category-five tropical cyclones have occurred with some regularity overall.
It’s worth mentioning Ilsa has formed pretty late in the cyclone season. Although the Bureau of Meteorology does say cyclones can form any time of the year, its very rare for this to happen outside of April.
Historical trends and climate change projections suggest the number of landfalling cyclones in our region will decrease over time. This has been clear and consistent with real-world data, and puts Australia at odds with other regions of the world, where cyclone frequency is increasing.
However, most climate models also predict that a greater proportion of these cyclones will be of a higher strength. The current scientific consensus is that we’ll experience these events less often, but when we do, they will be more intense.
Reuters
Fri Apr 14 2023
A Bureau of Meteorology satellite image shows Tropical Cyclone Ilsa at 10:30 AM AEST on April 13, 2023. - AAP Image/Bureau of Meteorology/via REUTERS
ISIS Malaysia's perspective of Budget 2025
An excellent rakyat-centric budget under the overarching principle of a caring and humane economy.
Budget 2025: Record increase in STR, SARA aid initiatives
The government will provide a significant boost to the Sumbangan Tunai Rahmah (STR) and Sumbangan Asas Rahmah (SARA) initiatives next year.
Budget 2025: EPF contributions to be made mandatory for foreign workers – PM Anwar
The government plans to make it compulsory for all non-citizen workers to contribute to the Employees Provident Fund (EPF).
What policies to expect from Indonesia's new President Prabowo
Prabowo will be open to foreign investment, his aide has said, such as by offering investors management of airports and sea ports.
Budget 2025: Govt allocates RM470 mil to empower women's participation in PMKS
The Women's Leadership Apprenticeship Program will be intensified as an effort to produce more female corporate personalities.
Israel sends more troops into north Gaza, deepens raid
Residents of Jabalia in northern Gaza said Israeli tanks had reached the heart of the camp, using heavy air and ground fire.
Indonesia ramps up security ahead of Prabowo's inauguration
Prabowo Subianto will be sworn in as Indonesia's president on Sunday with Vice President-elect, Gibran Rakabuming Raka, also taking office.
Immediate allocation of RM150 mil for local authorities, DID to tackle flash floods
Datuk Seri Anwar Ibrahim said this allocation is intended to address the recent flash floods that hit the capital and several major towns.
Budget 2025: Sabah, Sarawak to continue receiving among highest allocations - PM
Sabah and Sarawak continues to be prioritised under Budget 2025, with allocations of RM6.7 billion and RM5.9 billion respectively.
NFOF will be operational in November 2024 with funding of RM1 bil
PM Anwar Ibrahim said NFOF will support venture capital fund managers to invest in startup companies with RM300 million set aside for 2025.
Minimum wage to increase to RM1,700 effective Feb 1, 2025
The Progressive Wage Policy would be fully enforced next year with an allocation of RM200 million, benefiting 50,000 workers.
Bursa Malaysia ends higher on Budget 2025 optimism
The benchmark index, which opened 1.85 points higher at 1,643.29, moved between 1,641.71 and 1,649.31 throughout the trading session.
Five important aspects relating to people’s lives in Budget 2025 - PM
The focus is on driving the MADANI Economy, speeding reforms, cutting red tape, raising wages, and tackling the cost of living.
Economic outlook: Govt plans to leverage, expand existing city transit system
The expansion aims to provide a more efficient and reliable public transportation network, reduce congestion, and improve accessibility.
Economic outlook: Budget 2025 to lay foundation for a digital-driven economy
The report said Budget 2025 will entail efforts to position Kuala Lumpur as a top 20 global startup hub by 2030 through the KL20 initiative.
Economic outlook: Corruption and lack of accountability hinder economic progress
Special Cabinet Committee on National governance is established to curb corruption, law reforms to modernise outdate regulations, MoF said.
National Wages Consultative Council will be strengthened
The govt will also incentivise hiring women returning from career breaks, offer job matching and improve care services facilities.
Economic outlook: Ensuring 11 years of compulsory education for all children
Budget 2025 will continue prioritising upskilling and retraining initiatives to equip workers with the latest skill sets necessary.
Consolidated public sector projected to record lower surplus of RM41.7 bil 2024
The MoF said the consolidated general government revenue is estimated to increase slightly to RM384.7 billion in 2024.
PM announces substantial Budget 2025 hastening Malaysia to become Asian economic powerhouse
Datuk Seri Anwar Ibrahim said it would create jobs and also tackle financial leakages to enhance public spending efficiency.