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General Discussion >> Hurricane Ask/Tell

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danielwAdministrator
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HurriSheet... Intensity and Surge Estimations from Pressure
      #74471 - Mon Apr 30 2007 10:48 PM Attachment (317 downloads)

UPDATED 19 April 2009... see the Google links at the bottom of this post.

Some quick formulas for estimating Hurricanes:

From 1013mb to 1000mb-A 1mb drop, in pressure, equals a 5mph increase in windspeed.

From 1000mb to 890mb- A 1mb drop, in pressure, equals a 1 mph increase in windspeed.

Delta P-or change in pressure:
After a storm reaches 75mph. A rough estimation of the Maximum Possible Windspeed (at Flight Level or 10000 feet) may be assumed by using the following formula.
1000 - present pressure in mb= deltaP
deltaP + 75 = Rough estimate of the Max Poss Wind.

eg. Katrina 1000-902=98+75= 173mph
eg. Rita 1000-899=101+75=176mph

more to follow...
(these have not been peer reviewed)

Storm Surge estimation:
1010mb- Storm's lowest pressure/ 4 = maximum possible storm surge, in feet.
Katrina__ 1010-902=108 / 4 =27feet
Rita_____1010-937= 73 / 4 = 18.25feet ( at landfall)

See Attachment, above, for a printable jpg of the HurriSheet.

Google Online Spreadsheet here: HurriSheet Spreadsheet
HurriSheet PDF.. ready to print

Edited by danielw (Sat Mar 31 2012 10:46 AM)


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Lamar-Plant City
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Re: HurriScale [Re: danielw]
      #74477 - Tue May 01 2007 04:55 PM

Where did this come from....if you don't mind me asking? This looks like something I will have to try out this season. I have always thought more in terms of every 20-25 mB below 1000 was fairly well related to in increase in category if you figure 1000 as the transition zone from TS to Hurricane. This is more complicated, but may work out better in the 'real world'.

--------------------
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danielwAdministrator
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Re: HurriScale [Re: Lamar-Plant City]
      #74483 - Thu May 03 2007 01:58 AM

It's is something that literally jumped out at me while doing some spreadsheet work.
I took the standard Saffir-Simpson Category numbers. Placed them on a spreadsheet. And filled in the gaps at 5mb intervals.


(NHC/TPC No longer uses minimum central pressure to classify Tropical Cyclones. That practice ended in the mid 1990s)

Using the above table:
980mb= 95mph or 82 knots
965mb=110mph or 95 knots__(15mb drop = 15mph increase)
945mb=130mph or 113 knots_(20mb drop =20mph increase)
920mb=155mph or 135 knots_(25mb drop = 25 mph increase)

After a Storm reaches 75mph. There is roughly a 1mph increase in windspeed for every 1mb drop in pressure.
This is what I call the "Maximum Possible Windspeed" in relation to pressure and wind Only.
Both Katrina and Rita had Maximum Windspeeds OVER the Max Possible Windspeed.
In other words Katrina and Rita went above the Pressure : Wind curve.

For those that have a spreadsheet. Excel or other versions.
Row 1,First Column- 1013 (mb is column name)
Row 1, Second column-10 (mph is column name)
Row 2,First Column- 1012
Row 2,Second column- 15
Now use the "add" function to take Column 1 down to 875mb, and Column 2 to 200 mph.

You should now have the HurriScale table.

This is Not a proven formula. But you can compare it to The Supercanes of 2005. The basis for the formula is the Atkinson-Holliday formulas and theories of the early 1970's. And some other authors over the last 30 years.

I'm working on an easy spreadsheet that I can post.

http://www.google.com/search?hl=en&q=pressure+wind+relationship

http://ams.allenpress.com/archive/1520-0493/105/4/pdf/i1520-0493-105-4-421.pdf

http://www.aoml.noaa.gov/hrd/tcfaq/D1.html

http://www.unc.edu/~rowlett/units/scales/saffir.html


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Hootowl
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Re: HurriScale [Re: danielw]
      #74484 - Thu May 03 2007 07:10 AM

Wow - excellent!!!!!! I can actually follow this as hard as that may be to believe.

I hope you don't mind that I printed out your two posts. I want to have them handy to reference so I can try it out this season.

I look forward to seeing your "easy spreadsheet".

Dotty


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CoconutCandy
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Wind Loading and the Saffir-Simpson Scale [Re: danielw]
      #75878 - Fri Jul 20 2007 09:05 AM

I've read somewhere recently (and always something I've sort of "known about"), that the Saffir-Simpson Scale is NOT 'linear'.

That is, for example, a Cat 4 is not 'just' 4 times as strong as a Cat 1.

Something like each Catagory is 5 times(!) as strong as the previous category, in terms of the 'wind loading' on structures, so that ...

Cat 2 = 5 times the wind loading force as a Cat 1 ...
Cat 3 = 25 times the wind loading force as a Cat 1 ...
Cat 4 = 125 times the wind loading force as a Cat 1 ...
Cat 5 = 625 times the wind loading force as a Cat 1 ...

Which helps to explain, in part, why a MAJOR Hurricane (Cat 3 and above) is *SO MUCH MORE* destructive that a 'sniggling' Cat 1.

Maybe the factor '5 times' is on the high side, but the concept stays the same, whatever the 'factor'.

I'd be really curious to find out exactly how all this works, from a technical standpoint.

Can anyone help me out here? Any links to technical articles? Thanks. I think I'll go try Google. Laters ...


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audienceofone
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Re: Wind Loading and the Saffir-Simpson Scale [Re: CoconutCandy]
      #75879 - Fri Jul 20 2007 10:01 AM

I will try to find some technical articles in my library, but this is my understanding. (Experts, certainly let me know if I'm wrong) While there are some ties to the windspeed and surge effects, the original basis for the actual catagories was damage to man made structures. This is why the idea for adding a catagory 6 to the scale has been proposed. Originally, Bob Simpson had noted that there was no need for a catagory 6 on the scale because storms more powerful than cat 5 would cause serious damage no matter how well constructed. Because of recent technological advances, some have proposed that this is no longer the case and additional catagories are needed. While calculating windspeed and pressure with the scale may be linear, the potential damage is not. Just "google" the Saffir-Simpson scale and you can read the increasing damage potential of each catagory. Since the damage potential cannot be easily quantified (except in terms of dollars which doesn't help much if a storm hits a rural area) it's hard to put an increasing factor on the catagories themselves, but you can certainly see that the damage potential does increase exponentially. Hope this helps answer the question you were asking. As I said earlier, I will see if I have any technical articles on hand.

--------------------
"I can see from your zombie stare that you don't understand technical talk. Let me try it in a language I call, 'Liberal Arts Major.' It's blue."

2007 forecast as of 5-1-07, 16/9/5


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Ed DunhamAdministrator
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Re: Wind Loading and the Saffir-Simpson Scale [Re: audienceofone]
      #75886 - Fri Jul 20 2007 05:54 PM

From the Hurricane Research Division FAQ:

Subject: D5) How does the damage that hurricanes cause increase as a function of wind speed?
Contributed by Chris Landsea

Or to rephrase the question: Would a minimal 74 mph hurricane cause one half of the damage that a major hurricane with 148 mph winds? No, the amount of damage (at least experienced along the U.S. mainland) does not increase linearly with the wind speed. Instead, the damage produced increases exponentially with the winds. The 148 mph hurricane (a category 4 on the Saffir-Simpson Scale) may produce - on average - up to 250 times the damage of a minimal category 1 hurricane!

For additional reading, try HRD FAQ

Cheers,
ED


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IMTechspec
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Re: HurriScale [Re: Lamar-Plant City]
      #75891 - Sat Jul 21 2007 11:48 PM

first time post, and jumping into this late...
TIME, another parameter to consider if you want to wrap your hands around damage potential.
How long will a single story cinder block structure in Florida with a plywood roof and twenty year old shingles hold up to 120MHP sustained winds? 2 hours, 5 hours, 10 hours? I do not know, but I am darn glad Hurricane Charley, with it's mid level Cat2 winds, did not take it's time passing over my my house in Orlando.

This is just simple anecdotal testimony, but if Charley had taken three or four hours to make it's way past my home, I do not know if the place would have made it. As it is, my fifteen year old house and it's original roof was breached in the hour or so that Charley was in the neighborhood.

No we do not want to get into your house vs. my house and how it was constructed... Mine does appear to be pretty well built, better than other homes that I have had.

These storms are very gusty. Time can be a factor. I had one tree that defiantly stood up to Charley and survived easily, the rest were not so lucky. Hurricane Jeanne was on the low end of Cat1 here, but it lasted all day. That one tree almost went down. The roof over my garage was breached by Jeanne, even though it survived Charley just fine.

Does the duration of the storm also affect how long a storm surge stays ashore? Or how far it might go inland (of course topology is also a factor) .

The morning after Katrina made landfall on the Gulf Coast, water was still trying to find it's way back to the GOM in Biloxi. Big surge, big wind, long duration storm. What a mess.

Time is another parameter.


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dem05
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Re: HurriScale [Re: danielw]
      #75898 - Mon Jul 23 2007 01:08 AM

This is good info for the weather hobbiest's back pocket. I would like to indicate two things that should be remembered when using this though...

As Danial Pointed Out, the "clock starts ticking" in his formula when the storm reaches 75MPH. This is very important for a best estimate. For example, Wilma did not become a hurricane until she reached a pressure of about 977 mb. This low pressure was a function of the overall surrounding environment, which also had a very low pressure. The lowest pressure for Wilma was around 882 mb. If you initialized Wilma as a hurricane at 1000MB (Wich is not correct, remember it was 977mb), you would get a wind speed of roughly 193 mph. When initiallizing at 977mb, which is the correct pressure, the wind speed would 170mph...which is pretty close to the actual maximum sustained winds (which were around 175mph).

Also important to remember is that this is an estimate, not a perfect science. In addition, the equation does not have an adjustment factor for strengthening or weakening hurricanes...with particular emphasis on weakening storms. The pressure in a weakening storm is not very representative of it's actual maximum wind potential. An example would be Katrina prior to landfall, the maximum wind speeds decelerated much faster than the pressure rise. This is similar to most weakening storms, so the 1:1, Pressure:Wind convention will not work for weakening systems. But this is a pretty cool little tool for hurricanes otherwise.


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CoconutCandy
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Wind Loading and the Saffir-Simpson Scale [Re: Ed Dunham]
      #75900 - Mon Jul 23 2007 07:43 PM

Wow. This is all very interesting information. You've given me a lot to chew on. Thank you all for your replies.

First, a few relevant quotes:

>> How does the damage that hurricanes cause increase as a function of wind speed? The 148 mph hurricane (a category 4 on the Saffir-Simpson Scale) may produce - on average - up to 250 times the damage of a minimal category 1 hurricane!

>> TIME, another parameter to consider if you want to wrap your hands around damage potential ... These storms are very gusty. Time can be a factor.

>> No we do not want to get into your house vs. my house and how it was constructed...

>> In addition, the equation does not have an adjustment factor for strengthening or weakening hurricanes...

All these factors mentioned are certainly important in a 'real-world' scenario, but I guess my original thoughts were in a so-called 'idealized' environment.

Although the Saffir-Simpson Scale does qualitatively describe the kinds of damage that could be expected from each category, in addition to it's quantitative parameters, it doesn't answer, specifically, the 'Scale Factor' question I had proposed.

And yes, while the time factor is *certainly* a huge factor in the real world with any land falling hurricanes, (Charley vs. Jeanne), and the peculiar gustiness of tropical cyclones is also a real-world consideration, and even whether the storm is strengthening or weakening may play a role in the amount of destruction in any given area, what I am looking for an 'idealized' (purely mathematical) situation.

Here's my 'idealized' scenario: Wind velocity stays exactly the *same* for a given period (say, a 5 minute period), as in a wind tunnel experiment. The materials used in the construction of the 'test structure' are carefully determined and stays a constant for each of the 5 tests, for each of the 5 categories (min cat1, min cat2, ..., min cat 5). The size (square footage) of the exposed surface (perpendicular wall or sloped roof, etc.) is carefully taken into consideration and is an integral part of the equation.

Master Question: How much 'Wind Loading" (PSI per square foot per unit time, etc.) can be expected (measured) in this idealized scenario for each category of hurricane.

There must be some 'scale factor', as I mentioned in my above post that can be derived (determined) through carefully designed experimental procedures. Perhaps my proposed 'factor' of 5 might be on the high side, but it's pretty obvious it's not linear, and similar to an exponential scale, dramatically goes up as we get into a MAJOR hurricane, of Cat 3 and above.

I read this recently somewhere, so I think it's already been more or less worked out. Just forgot where I read it or what the proposed factor was.

But, on the flip side of the coin, you're all right: An idealized experiment doesn't help much if you're in a slow moving storm, in an older or weakly constructed building, the veering or backing directions of the wind as the storm passes by on the various parts (walls, roofs, etc.) of your house, orographic considerations, etc, etc.

These are all very important considerations for any one man in any one residence during the passage of any one hurricane. But there must be some 'pure science' at work here in an idealized world from which we can derive the sought after scale factor.

I've done a fair amount of research on google, and it appears the mathematics are quite complex and must take into account many complex variables. I didn't say this would be an easy question to answer.

Any additional thoughts, links, suggestions and the likes?


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danielwAdministrator
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Re: Wind Loading and the Saffir-Simpson Scale [Re: CoconutCandy]
      #75901 - Mon Jul 23 2007 08:25 PM

The modified Fujita scale should answer most of the questions posted here. I never thought that the simplicity of the HurriScale would make it more complex. Must be Science!

The correct title is "Enhanced Fujita Scale", but I prefer modified.

http://www.spc.noaa.gov/faq/tornado/ef-scale.html

Dr Mark Powell at the Hurricane Research Division produced this publication in 1995. The data shows that the wind damage is exponential to the wind speed.
http://www.aoml.noaa.gov/hrd/Powell/Real_time_Damage.pdf

Edited by danielw (Mon Jul 23 2007 09:25 PM)


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RevUp
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Re: HurriScale [Re: IMTechspec]
      #75903 - Tue Jul 24 2007 12:17 PM

As you've eluded to, trying to forecast wind damage gets pretty complex when you also take foliage and "soil condition" into account, as we found in central FL (2004). A great amount of the wind damage occurred due to fallen trees and weakened ground and root systems. Whatever survived Charley was weakened and more prone to damage, or to cause damage to structures. The entire landscape gets changed across an area hit by a major hurricane, and this likely increases the potential for damage in the future. Likewise, as many experts have pointed out, development along the coastal areas has vastly increased the $$ potential for devastating wind damage due to tropical cyclones.

I think we're doing pretty good just to be able to estimate the features and characteristics of a hurricane! Trying to come up with a standard correlation to the extent of wind damage in any given area is nearly impossible.

--------------------
"Let tomorrow worry about itself. Each day has enough trouble of its own."


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CoconutCandy
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Experimental Wind Loading Data [Re: RevUp]
      #75906 - Tue Jul 24 2007 08:40 PM

Thank you all for your replies and links.

They've been very interesting and have added to my understanding of the Saffir-Simpson Scale, and the 'Enhanced Fujita-Scale', as well.

However, I'm beginning to wonder if I've proposed my question on the wrong forum (thread). You see, this is really unrelated to the HurriScale as proposed by Daniel in the original post of this thread, as interesting as that topic is. Perhaps I should have posted a new topic (thread).

What I am *really* looking for, here, is a *number*. It could be either an integer, like 5, or a real number, like 4.7. Let's take the hurricane force wind speeds out of the 'real world' and put them in a 'petri dish'.

Allow me to re-state my question:

First, let's take 5 wind speeds, which stay *exactly* the same for the duration of the 'measurement', say 1 minute, as can be produced in a wind tunnel environment.

Min. Cat. 1 - 74 mph
Min. Cat. 2 - 96 mph
Min. Cat. 3 - 111 mph
Min. Cat. 4 - 131 mph
Min. Cat. 5 - 156 mph

In that wind tunnel, we'll have a 'surface' that's exposed to each of those winds for that 1 minute duration. Let's say, for simplicity, that the surface is a perpendicular 'wall' which exposes itself 'head-on' (flat-wise) to the force of the winds.

Now, for each of those winds, there is a "force exerted" on that surface, which can be *measured* as a function of 'unit area', whether pounds per square inch, per square foot, per square meter, whatever. I believe that the force is measured as (I might be wrong) newtons/m2, or newtons per square meter.

With me so far? Now let's make those measurements for each of the 5 'target' speeds, as listed above, representing each minimal category wind speed.

OK! We've just completed our wind tunnel tests and now have 5 numbers, one for each target wind speed, all expressed as newtons per square meter.

Now if we were to plot those numbers on some x/y axis graph, we should be able to determine (derive) how much stronger the force (wind loading) for each increasing category.

Perhaps the "Scale Factor" doesn't stay the exactly the same between each wind speed category. Perhaps it does.

But in any event, we should be able to say, within the realm of these carefully controlled experiments, just *how much stronger* the force exerted on a perpendicular surface (per square meter) would be for each increasing category.

Per my original post on the subject:

================================

... Something like each increasing Category is 5 times(!) as strong as the previous category, in terms of the 'wind loading' on structures, so that ...

Cat 2 = 5 times the wind loading force as a Cat 1 ...
Cat 3 = 25 times the wind loading force as a Cat 1 ...
Cat 4 = 125 times the wind loading force as a Cat 1 ...
Cat 5 = 625 times the wind loading force as a Cat 1 ...

Which helps to explain, in part, why a MAJOR Hurricane (Cat 3 and above) is *SO MUCH MORE* destructive that a 'sniggling' Cat 1.

Maybe the factor '5 times' is on the high side, but the concept stays the same, whatever the 'factor'.

================================

So, what I am REALLY looking for are those 'scale factor' numbers, which provides an (admittedly) highly idealized 'petri dish' view of the raw data. THAT'S IT !!

--------------------------------------------------------------------------------------

Now let me wrap up here. I fully understand that this 'idealized' scenario with its 'rigidly controlled' environment has but limited applicability to the 'real world', with it's many extenuating and complicating factors.

What are these extenuating and complicating factors? From previous posts ...

>>> TIME, another parameter to consider if you want to wrap your hands around damage potential ... These storms are very gusty. Time can be a factor.

So (1) how long a storm takes to pass by (fast moving vs. slow moving) any given area and (2) hurricanes are well know for their 'peculiar gustiness' which exacerbates the damage a storm can do.

>>> No we do not want to get into your house vs. my house and how it was constructed...

And, of course, there is the all important issue of (3) building construction, and the (4)shape of the residence (A-Frame, rectangular or L-shaped, the amazingly hurricane-resistant "Dome of a Home", etc.)

>>> In addition, the equation does not have an adjustment factor for strengthening or weakening hurricanes...

Whether a storm is (5) strengthening or weakening as it passes by and (6) how the wind veers or backs during storm passage, exposing different part of the structure to the strongest winds, and (7) direct eyewall passage, when winds come from exactly opposite directions after the calm eye passes.

If the same area (8) already experienced a cyclone passage a few weeks previously, already weakening some structures and (9) if the ground is already saturated, causing trees to uproot more easily and (10) if the trees were already damaged from a previous storm ...

I could go on and on providing examples or these 'extenuating and complicating factors', but I think you get the idea.

The replies to my post really show how 'well grounded' and pragmatic most peoples' perspective are, really focused on the 'real world issues', and what it means to them, their lives, their homes, their yards (trees), etc., and on how much damage any cat storm can be expected to produce, hence the referrals to various Saffir-Simpson charts and Fujita-Scale articles, etc. That's all very interesting and highly useful information.

But Alas! What I'm looking for are those wind tunnel experimentally-derived numbers, which, when plotted on some kind of graph, results in the much sought after 'scale factor'.

I think Ed was closest (in concept) in his reply that a min. Cat 4 is about 250 times more destructive than a min. Cat. 1. ( See? That's a 'scale factor' number! )

But I'm *not* looking at damage assessments, or *anything* to do with the various 'extenuating and complicating factors' as I laid out above.

Just a simple, 'idealized', mathematical construct how the wind loading on an exposed surface exponentially increased with each category strength increase.

Sorry for the long post; just thought it was important to lay out more clearly my proposed question, and *specifically* what I'm searching for. 'Just' a *number* !

Thanks for your reads and your interest and thanking you in advance if you can provide any insight, links or other info which addresses my inquiry.

Many Mahalos from Hawaii - Norm

Edited by CoconutCandy (Wed Jul 25 2007 05:40 AM)


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danielwAdministrator
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Re: HurriSheet... Intensity and Surge Estimations from Pressure [Re: CoconutCandy]
      #85363 - Tue Apr 14 2009 08:01 PM

I have update the HurriSheet quick reference guide at the top of the page.
Now includes links to a Google spreadsheet and Google PDF for easy printing.

This is only a pocket guide and gives rough estimates of weather extremes before and during Tropical Cyclone events.


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danielwAdministrator
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Re: HurriSheet... Intensity and Surge Estimations from Pressure [Re: danielw]
      #85369 - Wed Apr 22 2009 02:16 PM

The HurriSheet at the top of the page is an expanded version of the Saffir-Simpson Scale and includes storm surge and wave height estimations and approximations.

The left half of the sheet is mainly for estimating maximum wind speeds from the storm's barometric pressure as reported by NHC and reconnaisance aircraft. I used 1000mb for calculations on this side of the page.

The right half of the sheet gives Storm Surge, Significant Wave height and wave period estimations based on barometric pressure.

I used 1013mb for calculations on the right side of the page.
1013mb may be used for all of the calculations. The result will be lower maximum wind speeds and higher surges.
Not entirely a bad idea since Surge Flooding results in more deaths than wind.

Edited by danielw (Wed Apr 22 2009 02:45 PM)


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Storm Hunter
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Re: HurriSheet... Intensity and Surge Estimations from Pressure [Re: danielw]
      #85396 - Sat May 16 2009 01:53 PM

just a heads up this year the The Saffir-Simpson Hurricane Wind Scale (Experimental) has had a big makeover!

http://www.weather.gov/infoservicechanges/sshws.pdf
http://www.nhc.noaa.gov/aboutsshs.shtml

--------------------
www.Stormhunter7.com ***see my flight into Hurricane Ike ***
Wx Data: KFLPANAM23 / CW8771
2012== 23/10/9/5 sys/strms/hurr/majh



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danielwAdministrator
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Re: HurriSheet... Intensity and Surge Estimations from Pressure [Re: Storm Hunter]
      #85405 - Sun May 17 2009 10:00 AM

Based on Ike 2008's MCP of 935mb that would equate to a max possible surge of 19.5 feet.
Landfall windspeed maximum was 95kt or 110 mph that would roughly give a surge value of 12 feet.
Ike's surge was in the 12 to 19 foot range. At 99% of locations.

I use the Storm's lowest barometric pressure to calculate the maximum storm surge. Worked with Katrina and other Major Hurricanes. It's the worst case scenario... but gives a lot of margin for evacuation of lower areas.

Always use the storms lowest barometric pressure reported and you can't go wrong... or get wet.


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