A Mighty Wind
Feb. 2nd, 2011 07:33 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
peterbirksThe current coverage of Cyclone Yasi seems a bit thin on technical details, so here's a few (rather frightening) facts.
The cyclone that flattened 70% of Darwin in 1974, Cyclone Tracy, was only a category 4. Katrina, which caused such devastation to New Orleans, was actually a near miss.
After Cyclone Tracy, building regulations were tightened, but only to the extent that buildings are designed to resist winds of just over 260 kmh. Yasi's is likely to generate winds of 300kmh.
It's hard to describe how strong 300kmh is. It's basically a case of making sure that your car is tied down. Non-brick houses would be flattened and some brick structures would have problems. While the larger commercial buildings would survive, any "ordinary" buildings in the path of 300kmh would be seriously damaged. Yasi, in other words, could make Katrina look like a tea party.
Hurricanes work in a nasty way when you are directly in its path. You get a couple of hours of really strong winds in one direction, followed by a period of calm, and then a period of equally strong winds in the opposite direction. This "push me pull you" impact has a potential for far greater damage than sustained winds in a single direction.
And then there is what is laughably called "storm surge". If you get waves seven metres high (up to nine metres has been predicted), that's basically a tsunami.
Cairns has not covered itself in glory here. It warned 30,000 people to evacuate their low-lying homes, which they did, only to discover that it only had about 10,000 or so places at evacuation shelters. So the mayor told them to go back home and batten down the hatches. If deaths occur as a result, there could be political consequences.
In terms of economic cost, you will be lucky to get away with less than $3bn - and it could be as high as 10 times that (Katrina was $80bn in economic cost, btw).
So, worrying times for northern Queensland.
__________
The cyclone that flattened 70% of Darwin in 1974, Cyclone Tracy, was only a category 4. Katrina, which caused such devastation to New Orleans, was actually a near miss.
After Cyclone Tracy, building regulations were tightened, but only to the extent that buildings are designed to resist winds of just over 260 kmh. Yasi's is likely to generate winds of 300kmh.
It's hard to describe how strong 300kmh is. It's basically a case of making sure that your car is tied down. Non-brick houses would be flattened and some brick structures would have problems. While the larger commercial buildings would survive, any "ordinary" buildings in the path of 300kmh would be seriously damaged. Yasi, in other words, could make Katrina look like a tea party.
Hurricanes work in a nasty way when you are directly in its path. You get a couple of hours of really strong winds in one direction, followed by a period of calm, and then a period of equally strong winds in the opposite direction. This "push me pull you" impact has a potential for far greater damage than sustained winds in a single direction.
And then there is what is laughably called "storm surge". If you get waves seven metres high (up to nine metres has been predicted), that's basically a tsunami.
Cairns has not covered itself in glory here. It warned 30,000 people to evacuate their low-lying homes, which they did, only to discover that it only had about 10,000 or so places at evacuation shelters. So the mayor told them to go back home and batten down the hatches. If deaths occur as a result, there could be political consequences.
In terms of economic cost, you will be lucky to get away with less than $3bn - and it could be as high as 10 times that (Katrina was $80bn in economic cost, btw).
So, worrying times for northern Queensland.
__________
