Cyclone Seroja just demolished parts of WA – and our warming world will bring more of the same


Bureau of Meteorology

Jonathan Nott, James Cook UniversityTropical Cyclone Seroja battered parts of Western Australia’s coast on Sunday night, badly damaging buildings and leaving thousands of people without power. While the full extent of the damage caused by the Category 3 system is not yet known, the event was unusual.

I specialise in reconstructing long-term natural records of extreme events, and my historic and prehistoric data show cyclones of this intensity rarely travel as far south as this one did. In fact, it has happened only 26 times in the past 5,000 years.

Severe wind gusts hit the towns of Geraldton and Kalbarri – towns not built to withstand such conditions.

Unfortunately, climate change is likely to mean disasters such as Cyclone Seroja will become more intense, and will be seen further south in Australia more often. In this regard, Seroja may be a timely wake-up call.

Seroja: bucking the cyclone trend

Cyclone Seroja initially piqued interest because as it developed off WA, it interacted with another tropical low, Cyclone Odette. This rare phenomenon is known as the Fujiwhara Effect.

Cyclone Seroja hit the WA coast between the towns of Kalbarri and Gregory at about 8pm local time on Sunday. According to the Bureau of Meteorology it produced wind gusts up to 170 km/hour.

Seroja then moved inland north of Geraldton, weakening to a category 2 system with wind gusts up to 120 km/hour. It then tracked further east and has since been downgraded to a tropical low.

The cyclone’s southward track was historically unusual. For Geraldton, it was the first Category 2 cyclone impact since 1956. Cyclones that make landfall so far south on the WA coast are usually less intense, for several reasons.

First, intense cyclones draw their energy from warm sea surface temperatures. These temperatures typically become cooler the further south of the tropics you go, depleting a cyclone of its power.

Second, cyclones need relatively low speed winds in the middle to upper troposphere – the part of the atmosphere closest to Earth, where the weather occurs. Higher-speed winds there cause the cyclone to tilt and weaken. In the Australian region, these higher wind speeds are more likely the further south a cyclone travels.

Third, most cyclones make landfall in the northern half of WA where the coast protrudes far into the Indian Ocean. Cyclones here typically form in the Timor Sea and move southward or south-west away from WA before curving southeast, towards the landmass.

For a cyclone to cross the coast south of about Carnarvon, it must travel a considerable distance towards the south-west into the Indian Ocean. This was the case with Seroja – winds steered it away from the WA coast before they weakened, allowing the cyclone to curve back towards land.

Reading the ridges

My colleagues and I have devised a method to estimate how often and where cyclones make landfall in Australia.

As cyclones approach the coast, they generate storm surge – abnormal sea level rise – and large waves. The surge and waves pick up sand and shells from the beaches and transport them inland, sometimes for several hundred metres.

These materials are deposited into ridges which stand many metres above sea level. By examining these ridges and geologically dating the materials within them, we can determine how often and intense the cyclones have been over thousands of years.




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At Shark Bay, just north of where Seroja hit the coast, a series of 26 ridges form a “ridge plain” made entirely of one species of a marine cockle shell (Fragum eragatum). The sand at beaches near the plain are also made entirely of this shell.

The ridge record shows over the past 5,000 years, cyclones of Seroja’s intensity, or higher, have crossed the coast in this region about every 190 years – so about 26 times. Some 14 of these cyclones were more intense than Seroja.

The record shows no Category 5 cyclones have made landfall here over this time. The ridge record prevents us from knowing the frequency of less intense storms. But Bureau of Meteorology cyclone records since the early 1970s shows only a few crossed the coast in this region, and all appear weaker than Seroja.

Emergency services crews in the WA town of Geraldton, preparing ahead of the arrival of Tropical Cyclone Seroja
Emergency services crews in the WA town of Geraldton, preparing ahead of the arrival of Tropical Cyclone Seroja – an event rarely seen this far south.
Department of Fire and Emergency Services WA

Cyclones under climate change

So why does all this matter? Cyclones can kill and injure people, damage homes and infrastructure, cause power and communication outages, contaminate water supplies and more. Often, the most disadvantaged populations are worst affected. It’s important to understand past and future cyclone behaviour, so communities can prepare.

Climate change is expected to alter cyclone patterns. The overall number of tropical cyclones in the Australian region is expected to decrease. But their intensity will likely increase, bringing stronger wind and heavier rain. And they may form further south as the Earth warms and the tropical zone expands poleward.

This may mean cyclones of Seroja’s intensity are likely to become frequent, and communities further south on the WA coast may become more prone to cyclone damage. This has big implications for coastal planning, engineering and disaster management planning.

In particular, it may mean homes further south must be built to cope with stronger winds. Storm surge may also worsen, inundating low-lying coastal land.

Global climate models are developing all the time. As they improve, we will gain a more certain picture of how tropical cyclones will change as the planet warms. But for now, Seroja may be a sign of things to come.




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This article is part of Conversation series on the nexus between disaster, disadvantage and resilience. Read the rest of the stories here.The Conversation

Jonathan Nott, Professor of Physical Geography, James Cook University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

I’ve always wondered: who calls cyclones their names?


Richard Wardle, Australian Bureau of Meteorology

This is an article from I’ve Always Wondered, a series where readers send in questions they’d like an expert to answer. Send your question to alwayswondered@theconversation.edu.au


Who calls cyclones their names? – Guy Mullin, Mozambique.

In the Australian region, the Bureau of Meteorology gives tropical cyclones their name. You can write to the Bureau of Meteorology to suggest a cyclone name, but it is likely to be more than a 50-year wait.

Tropical cyclones are named so we can easily highlight them to the community, and to reduce confusion if more than one cyclone happens at the same time. The practice of naming tropical cyclones (or storms) began years ago to help in the quick identification of storms in warning messages. Humans find names far easier to remember than numbers and technical terms.

Aerial views of flooded areas following Cyclone Idai in March 2019.
EU Civil Protection and Humanitarian Aid Operations/flickr, CC BY-NC-ND



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Clement Wragge began naming cyclones in 1887

Tropical Cyclone Oma captured by NASA international space station.
NASA Johnson/flickr, CC BY-NC-ND

Now, people ask us all the time how we come up with the names for tropical cyclones. It started in 1887 when Queensland’s chief weather man Clement Wragge began naming tropical cyclones after the Greek alphabet, fabulous beasts, and politicians who annoyed him.

After Wragge retired in 1908, the naming of cyclones and storms occurred much less frequently, with only a handful of countries informally naming cyclones. It was almost 60 years later that the Bureau formalised the practice, with Western Australia’s Tropical Cyclone Bessie being the first Australian cyclone to be officially named on January 6, 1964.

Other countries quickly began using female names to identify the storms and cyclones that affected them.

Naming cyclones helps people quickly identify storms in warning messages. Cameras outside the NASAA international space station capture Hurricane Florence in 2018.
NASA Goddard Space Flight Center/flickr, CC BY-SA



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How cyclone names are chosen

While the world was giving female names to cyclones and storms, International Women’s Year in 1975 saw Bill Morrison, the then Australian science minister, recognise that both sexes should bear the shame of the devastation caused by cyclones. He ordered cyclones to carry both male and female names, a world first.

These days the Bureau is responsible for naming tropical cyclones in the Australian region, with the names coming from an alphabetical list suggested by the Australian public. These names alternate between male and female. The Bureau of Meteorology receives many requests from the public to name tropical cyclones after themselves, friends, and even pets.

The Bureau cannot grant all these requests, as they far outnumber the tropical cyclones that occur in the Australian region.

Trees on the side of the road at Mission Beach, North Queensland, in the aftermath of Cyclone Yasi, 2011. Cyclone Yasi formed in Fiji and maintained the name from that region’s weather agency.
Michael Dawes/flickr, CC BY-NC



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Cyclone Oma was named in Fiji

Cyclone names are reused, but when a tropical cyclone severely impacts the coast, or is deadly, like Debbie in 2017 and Tracy in 1974, the name is permanently retired for reasons of sensitivity.

If a listed name comes up that matches the name of a well-known person, or someone in the news for a sensitive or controversial reason, the name is skipped to avoid any offence or confusion.

When a cyclone forms in another region, say near Fiji or in the Indian Ocean, and then travels into the Australian region, the original name given by that region’s weather agency is kept, such as 2019’s Cyclone Oma, which came from Fiji.

Tropical cyclone Bessie was the first Australian cyclone to be officially named by the Bureau of Meteorology.

A list of cyclone names around the world can be found here.The Conversation

Richard Wardle, Weather Services Manager, Queensland, Australian Bureau of Meteorology

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Media Release: Wollumbin National Park


The link below is to a media release concerning the summit track at Wollumbin National Park, which was closed following extensive damage by ex-tropical cyclone Oswald in January 2013.

For more visit:
http://www.environment.nsw.gov.au/media/OEHmedia13053002.htm

AUSTRALIA: ENVIRONMENTAL DISASTER UNFOLDING ON QUEENSLAND COAST


An environmental disaster is unfolding on the Queensland coast, with the oil spill from the Hong Kong-flagged ship Pacific Adventurer. The Pacific Adventurer was badly damaged during the Cyclone Hamish weather event last week.

The Pacific Adventurer somehow managed to get caught up in the cyclone despite very early warnings concerning the cyclone. Some 31 containers containing ammonium nitrate were washed into the sea during the cyclone and as this occurred the ship itself was badly damaged, leaking some 230 tonnes of oil into the ocean. The initial report from the ship was that some 30 tonnes of oil had been lost.

The environmental disaster is huge, with the oil now affecting over 60km of coastline, including the eastern coast of Moreton Island. Sea life is being severely impacted by the disaster.

The cleanup is being done at a rate of about 1 to 2 km a day, which means it will take quite some time to complete.

Also of concern are the 31 containers of ammonium nitrate that are still missing and which could further contaminate the region. Navy mine hunters are being called in to search for the containers which remain a shipping hazard.