Tracking the storm: the science behind Tropical Cyclone Debbie


Liz Ritchie-Tyo, UNSW

Tropical cyclone Debbie has made landfall in Queensland as a category 4 cyclone with winds of more than 150 kilometres per hour. The Conversation

The cyclone crossed the coast near Airlie Beach on Tuesday afternoon. Reports of wind gusts in excess of 200km per hour and rainfall of more than 200mm of rain have been made in some areas along the central Queensland coast.

The Bureau of Meteorology forecasted an average to above-average number of Australian cyclones in its October severe weather outlook. Australia receives 11 cyclones on average each year, with about four of those in Queensland. Debbie is the fifth cyclone of the season for Australia as a whole and the most intense of the season so far.

Anomalously high moisture, warm ocean temperatures, and low environmental pressures seem to have created the conditions that allowed TC Debbie to form and grow in intensity.

Perfect storm

Tropical cyclones are low pressure systems that form over warm tropical oceans. The warmth and moisture of the oceans are what gives a cyclone its energy. The low pressure, which meteorologists measure in “hectopascals”, draws in the surrounding warm, moist air, which then rises into deep thunderstorm clouds. As the air is pulled into the centre of low pressure, Earth’s rotation causes it to spin cyclonically and it continues to intensify.

TC Debbie formed at the eastern end of an active monsoon trough extending from the Indian Ocean across the top of Australia and into the Coral Sea. The monsoon trough is a region of low air pressure and thunderstorms that forms over northern Australia in the summer months, bringing with it the wet season. On March 22, a large region of active thunderstorms began to organise into a weather disturbance off the eastern tip of Papua New Guinea.

Over the following two days the thunderstorms organised about a circulation centre as sea level pressures began to drop and moist air converged into the area. By late on March 24 a tropical depression, a forerunner of a cyclone, had formed and begun to drift south, making a long S-shaped track.

Tropical Cyclone Debbie was named on March 25. It then came under the influence of the subtropical ridge, a zone of stable high pressure that gives much of Australia’s fine weather during the summer. This drove Debbie west-southwest towards the Queensland coast while it gradually intensified further.

Because of the relatively high amounts of moisture in the atmosphere, and relatively warm ocean waters, Debbie intensified to category 4 by 10 pm on March 27, with the strongest wind gusts reaching 225-280km per hour. On Tuesday afternoon Debbie was a strong category 4 cyclone with a central pressure of 943 hectopascals and surface sustained winds of 185 kilometres per hour. The Bureau of Meteorology downgraded TC Debbie to a category 3 at 4:00 pm EST.

To put Debbie in context, there has been only one cyclone since 1980 to have made landfall in Queensland with a lower central pressure. That was Yasi in 2011.

Of the 46 cyclones to have made landfall in Queensland since 1980, only three others arrived at the coast with pressures of less than 960 hectopascals: Dominic in 1982, Winifred in 1986, and Ingrid in 2005.

Predicting cyclones

Tropical cyclone forecasters use a variety of tools to forecast the storm’s track, intensity, storm surge, and rainfall. Because it is difficult to obtain observations of wind at the ocean’s surface under a cyclone, meteorologists have developed tools based on satellite imagery to estimate a storm’s intensity, location, and where the strongest and most destructive winds are found.

Several models are also used to aid in making forecasts – from the complex numerical weather prediction models, to statistical models. Models start by using observations of the atmosphere, and then use these data to make a forecast.

Depending on their level of complexity the models can predict the future track, intensity, rainfall, wave height, and/or storm surge. The forecasters access all of this information to then make their forecast.

Cyclone forecasts have improved considerably over time. In particular, track forecasts have improved so that the 48-hour forecast is now more accurate than the 24-hour ones were back in the early 1990s. Track forecasting has become so reliable that the US National Hurricane Centre now produces 120-hour track forecasts.

Intensity forecasts have improved more slowly, but as models have become more refined and satellite technology has improved, the ability of forecasters to accurately estimate and predict intensity is also getting gradually better.

The prediction of rainfall, the extent of the damaging wind field, and storm surge forecasts are also slowly improving. Now that they are receiving more attention, we can expect considerable improvements in these over the next decade.

Liz Ritchie-Tyo, Associate Professor, School of Physical, Environmental, and Mathematical Sciences, UNSW

This article was originally published on The Conversation. Read the original article.

Cyclone Debbie: we can design cities to withstand these natural disasters


Rob Roggema, University of Technology Sydney

What happens after Cyclone Debbie is a familiar process. It has been repeated many times in cities around the world. The reason is that our cities are not designed for these types of events. The Conversation

So we know what comes next. Queenslanders affected by Debbie will complain about the damage, the costs and the need for insurers to act now to compensate their losses. The state and federal governments will extensively discuss who is to blame.

The shambles will be cleared and life will eventually get back to normal. Billions of dollars will be spent on relocating people and on repairing the damage and public works. A state-level levy may even be necessary to pay for all the extra costs. Two storms, Katrina and Sandy, cost the United States more than US$200 billion between them.

Yet we know what cyclones do. They bring, for a relatively short time, huge gusty winds. These are inconvenient but have proven not too damaging.

The greatest risk comes from storm surge and rainfall. Both bring a huge amount of water. And all this water has to find a way to get out of our living environment.

Despite knowing, approximately, where cyclones tend to occur, we never thought about adjusting our cities to their effects. It would make a huge financial difference if we did.

So, what can we do to build our cities differently to ensure the impacts of cyclones – and the accompanying rainfall and storm surges – do not disrupt urban life? The answer to all of this is design.

The usual design of current cities and towns brought us problems in the first place. We need to fundamentally rethink the design of our built-up areas.

Rethinking coastal and urban design

It starts with coastal design. We are used to building dams and coastal protection against storm surges happening once in 100 years. For comparison, the protection standards in the low-lying Netherlands are designed to protect the country against a once-in-10,000-years flood. But nature has proven to be stronger than our artificial constructs can handle.

An alternative design approach is to rely on the natural coastal processes of land forming – such as reefs, islands, mangroves, beaches and dunes. Humans can help the formation of these natural protectors by providing the triggers for them to emerge.

As an example, when we put sand in front of the coast, the currents and waves will transport the sand towards the coast and build up new and larger beaches. This example is realised in front of the Dutch coast and is known as the sand engine. But nature will build them up to form a much stronger system than humans ever could.

Instead of coasts, beaches and real estate being washed away, new land and larger beaches may be formed as a result of these processes. This requires design thinking, insights into the resilience of the coastal system, and understanding of the natural forces at play.

Second, urban design should reconsider the way we build our cities. Most urban areas do not have the capacity to “welcome” lots of water. And it is about lots of water, not the average shower or two.

Until cyclones are gone, these enormous amounts of water need to be stored for a short period in dense urban areas. This goes beyond water-sensitive urban design.

Despite the benefits of water-sensitive design in many urban developments, when the going gets tough, this is just not enough. Water-sensitive urban design can barely cope with average rainfall peaks. So, in times of severe weather events, cities need to have additional spaces to store all this water.

The general rule here is to store every raindrop as long as possible where it falls.

How and where should we redesign our cities?

So, what can be done to cyclone-proof our cities? We can:

  • Create larger green spaces, which are connected in a natural grid, increase the capacity of these green systems by adding eco-zones and wetlands, and redesign river and creek edges. Remove the concrete basins from every creek in the city.

  • Use large public spaces, such as parking spaces near shopping centres, ovals and football pitches, for temporarily capturing and storing excess rainwater. Small adjustments at the edges of these places are generally enough to capture the water.

  • Turn parking garages into temporary storage basins.

  • Redesign street profiles and introduce green and water-zones in streets. Out of every three-lane street, one lane can be transformed into a green lane, which can absorb rainwater.

  • Redesign all impervious, sealed spaces and turn these into areas where the water can infiltrate the soil. Use permeable materials.

  • Think in an integrated way about street infrastructure, green and ecological systems, and the water system.

These design interventions are not new and have been done abroad in cities such as Rotterdam, Hamburg or Stockholm. If we could add to these the redesign of roofs and gardens of industrial and residential estates and turn these into green roofs and rain gardens, the city would start to operate as a huge sponge.

When it rains, the city absorbs the huge amounts of water and releases it slowly to the creek and river system after the rain has gone. This way, green spaces and water spaces not only play an important role during and just after a cyclone, but they then add quality to people’s immediate living environment.

And maybe the best of all this: the bill Debbie and other natural disasters would present to government, industries and insurers could be much lower.

Rob Roggema, Professor of Sustainable Urban Environments, University of Technology Sydney

This article was originally published on The Conversation. Read the original article.

Queensland Galaxy: One Nation surges to 23%<


Adrian Beaumont, University of Melbourne

A Queensland Galaxy poll has One Nation surging to 23%, up 7 points since early November. One Nation’s gains have come at the expense of both major parties, with the Liberal National Party (LNP) on 33% (down 4), Labor on 31% (down 4), and the Greens steady on 8%.

While Labor maintains a steady 51-49 two party lead, the high non-major party vote makes this result a guesstimate. No fieldwork dates or sample size are given, but this poll was presumably taken between Tuesday and Thursday with a sample of 800-1000.

Of the three established parties, the Greens have been least affected by One Nation’s rise, indicating that demographics that vote Green are the least likely to swing to One Nation.

At the 1998 Queensland state election, One Nation won 11 of the 89 seats on 22.7% of the vote. If their vote in this poll were replicated at the next election, due by early 2018, One Nation would probably win a similar number of seats, and be likely to hold the balance of power.

Despite One Nation’s surge, Premier Annastacia Palaszczuk’s ratings are still positive, with 41% approval (down 3) and 37% disapproval (down 2), for a net rating of +4. However, Opposition Leader Tim Nicholls’ ratings have slumped a net 8 points to -12.

Federally and in other states, One Nation’s polling has met or exceeded their previous peaks from 1998-2001. It is no surprise that Queensland, which had the highest One Nation vote in 1998, is better for them than other states.

Whether One Nation and similar international parties continue to surge probably depends on President Trump. As I wrote here, if Trump succeeds in revitalising the industrial midwest, far right parties are likely to thrive. On the other hand, if working class people eventually decide that Trump is opposed to their economic interests, far right parties will probably decline.

The Conversation

Adrian Beaumont, Honorary Associate, School of Mathematics and Statistics, University of Melbourne

This article was originally published on The Conversation. Read the original article.

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