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General Discussion >> Hurricane Ask/Tell

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Lysis
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Saffir Simpson scale question
      #36051 - Thu Jun 02 2005 06:35 PM

On the Saffir simpson scale a tropical cyclone is classified in relation to its maximum windspeed. From this, we derive all the related components of the system (storm surge, etc). I realize that it is somewhat more complicated than that, but this is at least how it is from the public’s perception …which is where the scale was designed to register in the first place. Once the storm makes landfall, the intensity can be re-evaluated by looking at the damage caused, much like how they rate tornadoes on the Fujita scale.
My question is, to what building code is the Saffir Simpson scale based upon?
I think it was devised sometime in the early 70’s, but does it take into account the ever-changing building codes in a given area (for example, houses are built considerably different in Miami that they are in, say, New Jersey)?

Thinking along these lines, I came to the conclusion that the system may be flawed in other respects. Classification based on wind damage may not be the best approach for such a multifaceted natural disaster, which deals with intense rainfall and surge, as well as wind. For example, Charley was stronger at landfall at the barrier islands around Captiva and Punta Gorda, yet you could ride the storm out at the coast (granted you had something along the lines of a military bunker) with little difficulty. However I would never even think of camping out around the Fl panhandle/Gulf Shores coast when Ivan, a weaker storm, made landfall. Case in point, the surge and therefore immediate costal damage was far greater, yet the impact of Ivan was somewhat dampened by his lower status on the Saffir Simpson scale. Should the scale, then, be revised to accommodate the unique properties of every hurricane?

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ClarkModerator
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Re: Saffir Simpson scale question [Re: Lysis]
      #36062 - Fri Jun 03 2005 12:39 AM

Really good question...

The Saffir-Simpson scale was initially developed in the late 60s by Hebert Saffir, a civil engineer who wanted to be able to quantify the damages that various magnitudes of wind speeds from a hurricane could inflict upon the coast. Thus, while it may not be explicit, I would imagine the scale -- which has remained unchanged since the early 70s -- was written with late 60s building codes in place.

The initial emphasis was on the wind speed portion of the scale, though storm surge and various subjective damage estimates have been categorized along with the various wind speeds since then. Sometimes, you'll see pressure lumped in there too. (That brings up the whole debate about the best measure of a hurricane's intensity, pressure vs. wind speed, which I won't rehash in great detail now. Pressure is generally a better measure of the intensity, as when combined with the pressure of the environment of the storm, you can get a feel for what the wind is going to do via their direct relationship. However, it's the wind that causes the damage...in effect, one affects the other and vice versa. But I digress.) As we all know, however, two category 4 hurricanes, one moving fast and of a compact size and another moving slowly and of a larger size, are going to result in vastly different damage profiles upon landfall. How do you make up the difference? It's tough to do with any one scale, and that is why the Saffir-Simpson scale is necessarily broad. It's also a testament to our wave modellers and tropical forecasters in how they generally get the impacts of any given storm right.

Personally, my viewpoint is that the Saffir-Simpson scale is borad and indistinct enough to cover all possibilities within its categories. Motion, size, intensity, and the environment all play a role in what any given storm will do, meaning two storms of equal wind speed may have vastly different damage profiles. My feeling is that assuming equal wind speeds between two storms, despite these aforementioned differences, the overall damage patterns are going to be similar in magnitude -- minimal, moderate, extensive, extreme, or catastrophic for categories 1-5 respectively -- between the two storms.

In essence, from this viewpoint, it becomes an education exercise to the public as to what the scale really means and how best to interpret what a given storm will do to your region. This is much like the debate about the NHC maps that existed at the start of this year. While building codes are stricter today than they were in the past -- anything built to 1960s code along the coast isn't likely to make it through a category 2 hurricane, IMO -- the sheer increase in population & density along our coastlines makes up for the difference. While all homes won't be leveled, as they may have been in the 60s, many homes will suffer at least some damage, sort of negating the difference in building codes. Thus, I don't think this argues for the scale to be redesigned, just argues for a better understanding of a storm's impacts as it relates to the scale....perhaps clarification of various points of the scale, but not a redesign.

As an aside, with very intense hurricanes, trained observers will occasionally go in and survey the damage to help estimate the storm's intensity at landfall, but to a large degree, that estimation is still done largely with numerical data. For instance, the reanalysis of Andrew as a cat. 5 storm included both aspects, but relied heavily on observational data from radar, dropsondes, land-based anemometers, and similar stations. The reason for this is that it is tough to distinguish on a very fine scale between damage -- and in a lowly-populated area, you can get a vast underrepresentation of the damage due to a lack of structures to go off of. ith tornadoes, each category has a much wider expanse of winds, making categorization easier on a subjective basis. This debate was brought up with Charley a while back and is still valid here. There's no real answer I'm getting at here, just providing my viewpoint, but whether or not the Saffir-Simpson scale needs revising...hurricane intensity is generally an objective exercise and will likely remain so for the indeterminable future.

Just my two cents...but definitely a thought-provoking question!

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Lysis
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Re: Saffir Simpson scale question [Re: Clark]
      #36065 - Fri Jun 03 2005 08:21 AM

Excellent Clark, you answered some other questions I had as well. Would anyone here know exactly what the 1960's building codes were (in Florida)?

What prompted me to make this thread was the fact that most people here and in Port Charlotte erroneously think that they went through a CAT 5 with Charley, forcing them to conclude that they can successfully ride out any other storm with little difficulty or preparation. This is a product of a misunderstanding (as you said) of the scale itself, which, in this case, is facilitating a very bad mindset.


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cheers

Edited by Lysis (Fri Jun 03 2005 08:26 AM)


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Ed DunhamAdministrator
Former Meteorologist & CFHC Forum Moderator (Ed Passed Away on May 14, 2017)


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Re: Saffir Simpson scale question [Re: Lysis]
      #36127 - Mon Jun 06 2005 03:35 PM

The short answer is that if people in your area made the mistake once with Charley's intensity, they will (sadly) make it again with the next storm that impacts that area (of any intensity). No matter how much NHC and others try to educate the public, the process is only successful for those that listen and learn - unfortunately, that is not everyone.

Regarding intensity, the Fujita tornado intensity scale is based on the extent of damage as the primary factor - and I personally think that this is a bit foolish. If a 250mph tornado hits a cornfield in Texas, does that make it an F0? The primary factor for tropical cyclone intensity is windspeed - doesn't matter what the condition of the corn is. A good example is Hurricane Bret in south Texas a few years ago.
Cheers,
ED


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Lysis
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Re: Saffir Simpson scale question [Re: Ed Dunham]
      #42231 - Mon Jul 11 2005 07:20 PM

...exuse me, I know this is old, but I just wanted to know what you meant with bret in context with damage?

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cheers


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Terra
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Re: Saffir Simpson scale question [Re: Lysis]
      #42241 - Mon Jul 11 2005 07:44 PM

I must have missed this thread when it was originally written....

You can compare the Saffir-Simpson scale to the Richter scale for earthquakes. Both are quantitative scales, with Saffir depending on windspeed and Richter depending on magnitude (which is based upon amplitude of the largest wave in the seismogram and distance from the epicenter). However, it is possible that earthquakes of lower Richter magnitude can cause higher damage. You have to also consider population, construction of structures, nature of the ground surface, duration of vibrations, etc. For earthquakes, there is a second scale, the modified mercalli intensity scale that takes all of this into account and provides a qualitative description of the damage based on everything, not just magnitude. It ranks quakes from 1-12 based on which description bast fits what happend. Perhaps it would be cool if hurricanes had a similar damage scale....

Now, here's my question... what is the rational behind the size of the bins for the Saffir-Simpson scale.... I mean, wouldn't it have made more sense to make them the same size? See below:
Cat 1 74-95 mph (21)
Cat 2 96-110 mph (14)
Cat 3 111-130 mph (19)
Cat 4 131-155 mph (24)
Cat 5 >155 mph

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Terra Dassau Cahill


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Lysis
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Re: Saffir Simpson scale question [Re: Terra]
      #42253 - Mon Jul 11 2005 08:28 PM

What do you mean? I don't understand.

Now, here's my question... what is the rational behind the size of the bins for the Saffir-Simpson scale.... I mean, wouldn't it have made more sense to make them the same size? See below:
Cat 1 74-95 mph (21)
Cat 2 96-110 mph (14)
Cat 3 111-130 mph (19)
Cat 4 131-155 mph (24)
Cat 5 >155 mph



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cheers

Edited by Lysis (Mon Jul 11 2005 08:28 PM)


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Terra
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Re: Saffir Simpson scale question [Re: Lysis]
      #42256 - Mon Jul 11 2005 08:34 PM

Each number in parenthesis represents how many miles per hour of wind speed is represented by each category... Wouldn't it make more sense if each were the same rather than completely different?

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Terra Dassau Cahill


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Lysis
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Re: Saffir Simpson scale question [Re: Terra]
      #42260 - Mon Jul 11 2005 08:42 PM

Of course... sorry. I have a splitting migraine right now. I agree, that is very odd. Just another little idea, but along the same lines of thinking, I wonder if a category six rating would be appropriate. While rare... perhaps happening only once every decade or two, we have a storm that gets around 170-190mph. The destructive power of such a storm would be far greater than the 155mph wind requirement.

EDIT: Actually tera... I was thinking, and the numbers have rhyme and reason to them. A category four is literally a hundred times more destructive than a category two. This is because a winds destructive force increases exponentially. The brackets are calculated around the concept of what will destroy a certain type of structure (ie, a breaking point)… so that is the reason for the odd numbering.



--------------------
cheers

Edited by Lysis (Mon Jul 11 2005 08:45 PM)


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Terra
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Re: Saffir Simpson scale question [Re: Lysis]
      #42695 - Wed Jul 13 2005 04:27 AM

Is that true? I know the Richter scale is logrithmic, but I never heard that about the Saffir-Simpson scale.... That would seem logical, however, as you'd think those windspeed numbers were choosen for a reason. Not that I don't believe you, but can you send me some place to read about this...

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Terra Dassau Cahill


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Lysis
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Re: Saffir Simpson scale question [Re: Terra]
      #42709 - Wed Jul 13 2005 09:37 AM

Your guess is as good as mine. That was the only reason I could think for the odd numbering. I very well could be wrong.

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Allison
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Re: Saffir Simpson scale question [Re: Lysis]
      #42784 - Wed Jul 13 2005 04:06 PM

Quote:

...exuse me, I know this is old, but I just wanted to know what you meant with bret in context with damage?




Hi Lysis,

Bret was a major hurricane in 1999 that formed in the Bay of Campeche, rapidly intensified to Cat 4 and headed due north, scaring the bejeezus out of us here in Houston....

Then, it made a quick turn to the left -- scaring the bejeezus out of Corpus Christi -- and made landfall on the South Texas coast near Kingsville as a Cat 3. Fortunately, this area of Texas isn't highly populated (literally more cows than people), and there are few structures along the coast, thus drastically reducing the extent of wind damage one might expect from a Cat 3 if, for example, it had hit Corpus Christi or Brownsville.

I believe nearly all of the damage came from inland flooding, tornadoes, beach erosion, etc., and not so much from sustained hurricane-force winds.

Hope this helps!

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Allison


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Lysis
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Re: Saffir Simpson scale question [Re: Allison]
      #42797 - Wed Jul 13 2005 05:26 PM

Right! Thanks alot... that was bothering me for a while.

--------------------
cheers


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Multi-Decadal Signal
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Re: Saffir Simpson scale question [Re: Lysis]
      #42817 - Wed Jul 13 2005 07:32 PM

Does this elementary formula solve the relation between wind speed (v) and (v+n)? I know nothing of fluid dynamics other than it is a tricky and difficult branch of physics.

KE= 1/2 M V*2

I've been paying homeowners insurance for the 11 years I've been down here. Looks like they're finally going to have to pay off either this year or the next or the next...Of course they may leave the State or raise premiums to exorbitant levels.

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Who you gonna' believe?
Me, or your damn lying eyes?
_Ö_ _ö_


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