The destructive force is the wind pressure applied over the exposed area of the structure, which is a function of wind velocity squared times the exposed area of the structure. I did not mention kinetic energy but it also happens to be a function of velocity squared for something travelling at constant velocity. The power to sustain the velocity of an object moving at constant velocity in air is roughly a function of velocity cubed.
Your recollection may be confusing force, energy and power — all distinctly different physical properties. Yes, Rick, you are correct, I was confusing power with kinetic energy forgetting there is an integral between them. My bad…. Still does this not imply then that the destructive capacity of propelled items debris is a cubic function of wind speed?
Impact damage is usually related to kinetic energy but that implies consistent behaviour of the struck object, whether it is elastic deformation or yielding. With high winds denser objects can become airborne. As an example a brick moving at kph can penetrate better than a block of wood of the same weight also moving at kph. At impact the brick could penetrate a timber wall whereas the wood just makes a big thud. Both have the same kinetic energy but once an enclosed structure is penetrated the pressure change can cause rupture. AS-NZS goes into a good deal of detail on how structures should be designed for wind loads and flying debris.
A public hospital is deemed to be more important than say a private residence so the former is required to meet a higher standard.
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In small towns exposed to tropical storms it is not unusual to have at least one building that will stay safe in a yr event. People living in these areas should be aware of what a cyclone can do. I have lived in Dampier and Mackay.
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The Dampier residence was designed to withstand a Cat 5 storm. Old timber Queenslanders still standing have defied the odds. They are not a safe place in any cyclone and would be reduced to firewood in a Category 5. It is hoped no one living in them in the path of Marcia have the belief they have survived a Cat 5 cyclone. Yeppoon is supposed to have been the hardest hit. While I can find pictures of houses that have lost their roofs, and even some old decrepit shacks that have been completely destroyed, most photos show adjacent houses without any significant damage at all.
The trees look pretty good in Yeppoon. Some have been blown over, but they are not all stripped of foliage as would be expected in a category 5 storm. Earth Wind Map showing the eye crossing the coastline at 2pm 20th Feb. Thanks Gary.
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I tweaked the url to show the cyclone before it landed. The eye position at hours on Feb 19th was At hours it was Someone somewhere knows exactly where the eye went in relation to Middle Percy. The nullschool shot shows winds are stronger to the south and east, which fits with what TonyfromOz described as well. Jo, Fairfax published a U. Image of the cyclone just before the eye made landfall , which indicated how the eyewall passed through Percy Middle Island.
GDACS showed the the centre of the eye passed 24 km east of the weather station. The USN image shows an eyewall inner diameter of 45 to 50km not circular at sealevel before landfall. Given the trajectory , Middle Percy would have been at the very inside edge of the eyewall as it passed the island. Based on Google map scales the width of the peninsula it is just about to hit looks like it is 20km across E — W.
Where do you get the eye size figure? Thanks for pointing out the long lat. Looks like Middle Percy at Longitude was somewhere between Thats a big range.
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PS: Though looking at the google map above and the satellite image, Middle Percy looks very close to the action. It all depends on that trajectory. Jo, the image is not scaled, but the coast outline stretches from the tip of Cape Upstart at To estimate the eye size, I assumed that the eye was indeed circular and that the shadow at the eastern side which renders the eye elliptical was not the eastern edge of the eye. I overlaid circles to get the best fit. Noting the circular shape of the cloud top of the eye wall, I assumed that it should be concentric with the eye.
Accordingly, the diameter of the eyewall cloud top appears approximately the same as in the 11pm TRMM infra red image- about 60 km.
The eye appears to have a diameter just over 40 km. So the eyewall diameter should be intermediate, but close to the eye. Gary, the nullschool vizualisation shows the eye crossing the coast between 8am and 11am on the morning of the 20th. That is consistent with the BOM cyclone track map, which shows the eye location some 20km west of the Samuel Hill weather station. That wind speed reading should be of interest.
Imagine the outcry if they called them a Category 2 and they did turn out to be Category 5. They could then claim their prediction was correct, and that they were following Standard Practice as in temperature trends. Major improvements were later implemented in atmospheric observation, relevant computer models, and the training of forecasters.
I was living in southern England at the time and remember the eerie quietness as the eye came over us and a degree change of wind direction afterwards. There was massive damage. I was holidaying across The Channel , in Brittany at that time and thinking the breazy weather was just a feature of that area. We were without power for over a week on getting back to England.
In question time this afternoon Mr. Every cyclone causes damage and hopefully this will repaired quickly for those unfortunate enough to be affected. However, it is possible they are quoting satellite estimated wind speeds, which are measured well offshore.
This was done with Typoon Hagupit in the Philippines last year. By the time these big storms come ashore, their winds have slowed dramatically. They pine for the tragedies of the good old days when hundreds or even thousands of people were killed in floods or bushfires or famines , some event that would give some proof to their religion. Rather than be overjoyed that their theories might be wrong and mankind is not going to fry or starve or freeze etc. They would rather millions die rather than be proven wrong.
Ironically most of the death and suffering is caused by global warming policies which mean that electricity becomes too expensive or unreliable, Countries waste billions that could be spent on social benefits that support the poor and needy. Global Warming alarmism is the greatest moral issue of our time. A very valid point. Just think of what could be done to benefit mankind rather than waste it on erroneous computer models and nerds. Interested in what the government of Singapore, replete with extremely well qualified people who studied at Cambridge, Yale and Havard….
I would be surprised if very much. My mom is at Serina. The cyclone was forecast to go straight over her house, but passed south about km. They got 15mm of rain and zero wind at all. I suppose she should be very happy about that. Her husband Tom was one of the first into Darwin after it was hit by cyclone Tracy.
He also was very critical of the bom reports of this cyclone using colourful Australian language liberally. I have not seen any BOM information on this point. People believe the television, even my wife.
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Not even citing Tracey, which was a Cat 4, seemed to work. I feel for you. My mother is the same way. And once told it is extremely difficult to inform her otherwise. For people like that it allows them to gossip on the phone with their friends about whatever the latest news story is convinced of how smart they are without investing any time or effort in actual thought.
Some people will be influenced by that sort of nonsense, and you can put good money on there being no apologies or corrections. The assertion that Marcia was a Cat 5 based on modelling 20 kms away from MP island rather than the actual data from monitoring stations raises a problem.
If Marcia was at one stage a Cat 5, and thus recorded as such, how many other cyclones in the past would need to be re-examined to ascertain their category? They too may have reached Cat 5 level even though land based measurements would have measured them to be lower. Enough to maintain employment for 20 years for not-otherwise-required Climatologists.
They call it Plan B. I suspect that TC Marcia was at the same category level as Aivu which was either a 3 or 4 at the time. The winds were strong prior to Aivu touching down. Honestly, Jo. Who cares about the raw wind speeds? That is just so Enlightenment. Its the adjusted wind speeds that are the basis of all press releases. Clearly after adjustments the system was deemed Cat 5.