Cat 4 hurricanes very unlikely north of Florida on E Coast

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jaxfladude
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#41 Postby jaxfladude » Fri Jul 07, 2006 6:50 pm

I live at roughly 30.2N 81.3W so if I take the thought process right it is unlikely that I will experience high Cat 4 or Cat. 5 hurricane conditions........right?

Not I would want to go through one bad hurricane at all..........

New Edit: Hurricane Dora in 1964 was the last hurricane most directly impact this area. The link is to the Wikipedia page about Dora(there is some debate of Wikipedia's reliability of being factual so take the info herein with a grain of salt.)

http://en.wikipedia.org/wiki/Hurricane_Dora
Last edited by jaxfladude on Fri Jul 07, 2006 7:04 pm, edited 4 times in total.
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#42 Postby wxman57 » Fri Jul 07, 2006 6:50 pm

Matt-hurricanewatcher wrote:I don't think so a cat1 would not do the same level of surge as a cat5. Why because of strong winds moving over the surface of the ocean...Which builds waves height like any storm. The more winds moving across the ocean the higher the waves will be(Storm waves). Also the deeper the pressure the large the mound/surge will form under the center of the cane.

A cat1 will not bring nearly as high of a surge as a cat5. In fact if you get a cat5 over the gulf unlike winds water works alot slower. So its likely to stay that way for 12 to 24 hours if not more after weaking.

So if you have a cat5 8 hours before landfall. The winds will go down but the water will not. Yes the size of the area of winds are importand, and can increase the level of storm surge. But the fact is katrina was a cat5.


I'm not sure if you're referring to my post, Matt, but I can respond. As a marine meteorologist (forecasts wind waves and swells) for many of the past 26 years, wave height depends upon 4 main factors (in no particular order):

1. Wind fetch size (distance over which the wind blows across the water)
2. Wind duration
3. Average wind speed across the wind fetch area
4. Water depth

It would be quite possible for a Cat 1 hurricane with 74+ mph winds extending over a fetch distance of 100-150 miles to generate larger waves than for a Cat 5 hurricane that has 160 mph winds over only a 20-30 mile fetch area. Size of the max wind field is extremely important in determining wind fetch area, and thus wind duration over the fetch and the resulting wave height.

As for the water depth part, a wave will break when its height reaches 2/3 the water depth. So, no matter how strong the wind or how long the fetch, you cannot get more than, say, a 40 ft wave in 60 feet of water.

So, a Cat 1 hurricane with a very large area of 74-95 mph winds could produce a larger storm surge than a Charley-type Cat 5 with Cat 5 winds over a few square miles. Once again, there is no such thing as a "Cat 1 surge", "Cat 3 surge", or a "Cat 5 surge". Saffir-simpson deals only with peak winds in any small region of a hurricane.
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#43 Postby windycity » Fri Jul 07, 2006 6:58 pm

i would like to take a few minutes to thank our wonderful pro. mets, Derek and wxman,for the time and effort that they spend on this board.For us!!! I have learned so much, and i thank you. :D
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#44 Postby Matt-hurricanewatcher » Fri Jul 07, 2006 7:00 pm

I see what your saying wxman57...
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#45 Postby jaxfladude » Fri Jul 07, 2006 7:02 pm

windycity wrote:i would like to take a few minutes to thank our wonderful pro. mets, Derek and wxman,for the time and effort that they spend on this board.For us!!! I have learned so much, and i thank you. :D


I second that!!!!!!!
Let us hope that we do not need their expertise this year if and when the meat of the hurricane season comes this Aug to Mid. Oct.!
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#46 Postby storms in NC » Fri Jul 07, 2006 7:16 pm

Okay Now would you have had said I would have had 16' of water on my land in my house in sept 1999 when Floyd came thought. I DO NOT live in a flood plain. No boby thought this would happen. When I called 911 they wouldn't tell me nothing. All they would say was ( do you need someone to get you )That was it. Hubby on fire dept. Had no way of knowing either. For all raidos were dead. battarys were ran down for being on stay by. So that shows any thing can happen.

And as for Hugo. There was boats on the Instate 95. I don't think it was a cat 5 but I know it had to be on the low side of a cat 4

Katrina was bad. I had to cut my way though as I drove though there. I was alone and drove from NC to there and back. I was there for a month and when I went home as I drove though some towns it still looked like a bomb went off. It took some places 2 months to get lights and this was 60 miles northeast of NO. She did not have time to wine down her speed her winds still was felt as her surge. If she would have stayed out in the water for a day or 2 It wouldn't have been so bad.

Oh and by the way this 50 year old lady can do any thing.

I do beleave that the east coast will have thier turn this year for hurricans. I think we will see a few.

I wish Everyone the best this year. I think we are in for a summer like last year.
8-)
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#47 Postby Audrey2Katrina » Fri Jul 07, 2006 7:19 pm

As for Hugo being a 5, the NHC report indicated that at landfall, flight level winds were 141KT, and this flight level was at 12,000 feet, where a 95-100% reduction factor is used


We've already seen how fickle reduction factors are. Frankly since we've heard over and OVER again how much the wind speeds go up a category every so many feet or so vertically, I rather doubt that the wind speeds at 12,000 feet would be equal to those at ground level... extremely unlikely and IMO wild speculation at best. This also fails to address a ground central pressure of 935-940 mb at landfall, it is virtually inconceivable, especially given the size of Hugo (hence the spread of the isobar gradient) that it could have been anywhere near a Cat 5 at that pressure. Nope--just doesn't appear possible at all.

Therefore, since the motion was about 25 m.p.h., the winds in the nrothern eye wall should be about 50 m.p.h. stronger than Charleston received


This would be making more assumptions. First, it assumes that the exact track of the storm's movement puts Charleston in a position "parallel" to the wind's direction--physically this is the only way that you would get a 100% effect of forward motion working against measured wind speeds... the angle in which the storm came in is not consistent with a 25mph movement relative to Charleston. Additionally, if I were moving on a N bound train at 25 mph, and threw a ball with a speed of 100 mph (okay, so let's say it was Nolan Ryan at his peak) at EXACTLY the opposite direction--south, it would make the net speed 75 mph... a 25 mph reduction, not a 50 mph reduction--and that with "perfect" conditions for such a reduction to take place, which we know didn't prevail here at all--I doubt seriously that there was a 50 mph differential in "sustained" winds from Charleston, to the area of greatest windspeeds. Not proveable; but I simply disagree on its plausibility. Again, with all due respect I find your opinion to be highly speculative with a lot of "should be" and mathematical calculations which are not founded on actual surface observations--anywhere.

I reiterate that it's not even remotely possible IMO that Hugo was even close to being a 5 at S.C. landfall.

Nobody, for all their expertise or number crunching can or will prove anything beyond any shadow of doubt regarding Hugo... or Katrina... or, for that matter any hurricane until they can have reliable ground based data that lasts the duration of the storm AND catches all the areas of possible max winds--and we know how unlikely that is even in the near future. At least that's this one man's opinion, and I'm sticking to it! :wink:

A2K
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#48 Postby AussieMark » Fri Jul 07, 2006 8:01 pm

a hurricane intensity is based on wind speed not pressure
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#49 Postby Derek Ortt » Fri Jul 07, 2006 8:22 pm

Audrey, you're justa tad bit mistaken here

Thermal wind balance requires that for a vortex like Hugo, which is intensifying and has no trough interaction, that the strongest winds will be at the top of the boundary layer, which is about 1500 feet (which is why the most severe reduction factor is used there). The winds reduce with height, and 700mb, lower than the Hugo flight, yields 90%, which is 125KT, so higher up yields an even higher wind (NHC uses 100% for the 650 level)

Also, don't use the pressure to equate to a wind speed, unless we have nothing else. Iris was 125KT and barey below 950mb. Therefore, a flying 934mb hurricane that is not baroclinic can support cat 5 winds very easily
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#50 Postby Matt-hurricanewatcher » Fri Jul 07, 2006 8:34 pm

A large area fetch of winds over water will equal more storm suge/wind waves. But the stronger the winds are the faster=less area needed to gain the the height of the wave. So a cat3 hurricane 300 miles across can most likely do about the same as a tropical storm which is 900 or so miles across. Wind fetch...So what Derek in Wxman57 is getting at is area/fetch of winds over the ocean...Which also with a strong winds(I believe)can increase the height/energy faster. Is this true?
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#51 Postby Matt-hurricanewatcher » Fri Jul 07, 2006 8:51 pm

AussieMark wrote:a hurricane intensity is based on wind speed not pressure



The pressure grade from the inside to outside of the storm makes the winds. The tighter the pressure field is most of the time means stronger winds. You also look at a extratropical system that winds blow from high to low pressure...Which is like a valley the steeper it is the faster(The less space between the high and low)the winds flow. The closer/more intense the grade the stronger the winds.


Its like getting into one of those store baskets.

1# You have a flat surface you go no where. No pressure difference.
2# You have a 2 feet drop every 10 feet=1/5 incline you will start moving. The area of low pressure starts to devleop.
3# You have 5 feet drop every 10 feet or 1/2 which is a sharp drop. Your low pressure you are moving pretty fast.
4# You have a 8 foot drop every 10 feet in you will be going almost face first. Your low pressure bombs.
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#52 Postby Hybridstorm_November2001 » Fri Jul 07, 2006 8:51 pm

The argument that size is a factor is a correct one. Other factors that must be taken into account are; a) the natural tide cycles, b) the shape of the coastline the hurricane hits, c) the depth of the water in the shoreline basin, and finally d) the angle at which the eye comes into land, and thus that the winds are blowing at (either onshore or offshore). If all the conditions come together just right, then yes a cat 1 can have a cat 3, or in very extreme cases a cat 4, surge.

The Saxby Gale of 1869 caused an enormous storm surge in the Gulf of Maine/Bay of Fundy area, even though it was down from a cat 3 to a cat 2 at the time of landfall. It actually pushed the Saint John River back 50 miles against the natural flow, and rose the water level at least 6 ft at Frederiction, NB. The reasons it was able to do so is because; 1) it had built up a high surge when it was a cat 3, or even cat 4 the days before, 2) it arrived at High Fall tide that year, 3) it had a forward speed of 40 mph helping drive the waves even stepper.
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#53 Postby Normandy » Fri Jul 07, 2006 9:25 pm

Derek Ortt wrote:Charleston was in the SW half, where the speed of motion was against the wind. Therefore, since the motion was about 25 m.p.h., the winds in the nrothern eye wall should be about 50 m.p.h. stronger than Charleston received (CHARLESTON EXPERIENCED A CAT 1/2 HURRICANE, NOT A 4)

As for Hugo being a 5, the NHC report indicated that at landfall, flight level winds were 141KT, and this flight level was at 12,000 feet, where a 95-100% reduction factor is used



Well, lets do some simple math.

Charleston recieved 90 mph winds from Hugo, and lets assume it was 100% against the forward speed of motion from Hugo.

90mph + 50 mph = 140 mph

Thats 15 mph below the cat5 threshold, and right on with the sustained winds that the NHC gives Hugo right now.
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#54 Postby Derek Ortt » Fri Jul 07, 2006 9:44 pm

but some areas may have received higher winds, whcih also has to be allowed for (also, how far inland was the sustained report of 87? It if was a few miles inland, winds on the barrier islands may have been one cat higher).

Regardless, few if any experienced the cat 4/5 winds
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#55 Postby Patrick99 » Fri Jul 07, 2006 9:57 pm

I don't think it would take much for a Cat. 4+ to hit Tampa. Shift Charley a little bit to the north, and there you go. Plus, don't forget October Wilma-like storms coming up from the Caribbean. Wilma's Yucatan jaunt saved S. FL from an easy Cat. 4, possibly a 5. It could have easily been Tampa, with a bit slower of a trough.

Otherwise, I would agree.....Cat 4 north of S. Florida is rare, indeed...just look at all the known tracks. In fact, I might say that a landfalling Cat. 5 is *near* impossible (under current known climate conditions) north of Vero Beach. Key West-to-Jupiter is a pretty favorable stretch for a Cat. 5 to hit....you just don't see that weakening-just-before-landfall thing here. On the contrary, storms make that last run-up in intensity over the Gulfstream...the 1935 storm, Betsy, Jeanne and certainly Andrew come to mind.

I remember we were told that Andrew had "weakened" to a low-grade Cat. 4 over the Bahama Bank, as if that was going to be some big relief. Well, it wasn't, and the Gulfstream saw to that.
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#56 Postby wxman57 » Fri Jul 07, 2006 10:11 pm

Audrey2Katrina wrote:
Therefore, since the motion was about 25 m.p.h., the winds in the nrothern eye wall should be about 50 m.p.h. stronger than Charleston received


This would be making more assumptions. First, it assumes that the exact track of the storm's movement puts Charleston in a position "parallel" to the wind's direction--physically this is the only way that you would get a 100% effect of forward motion working against measured wind speeds... the angle in which the storm came in is not consistent with a 25mph movement relative to Charleston. Additionally, if I were moving on a N bound train at 25 mph, and threw a ball with a speed of 100 mph (okay, so let's say it was Nolan Ryan at his peak) at EXACTLY the opposite direction--south, it would make the net speed 75 mph... a 25 mph reduction, not a 50 mph reduction--and that with "perfect" conditions for such a reduction to take place, which we know didn't prevail here at all--I doubt seriously that there was a 50 mph differential in "sustained" winds from Charleston, to the area of greatest windspeeds. Not proveable; but I simply disagree on its plausibility. Again, with all due respect I find your opinion to be highly speculative with a lot of "should be" and mathematical calculations which are not founded on actual surface observations--anywhere.

A2K


Actually, you do not add a hurricane's forward speed to the winds on the right side. Recon measures/reports ground-relative speeds and that's what goes on the advisory. So storm motion is already taken into account in the advisory.
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#57 Postby wxman57 » Fri Jul 07, 2006 10:13 pm

Normandy wrote:

Well, lets do some simple math.

Charleston recieved 90 mph winds from Hugo, and lets assume it was 100% against the forward speed of motion from Hugo.

90mph + 50 mph = 140 mph

Thats 15 mph below the cat5 threshold, and right on with the sustained winds that the NHC gives Hugo right now.


Again, a 90 mph hurricane moving at 50 mph has 90 mph winds. Now it would likely have much lower winds to the left of the track, as the 90 mph max winds reported by the NHC already incorporate that fast forward speed to the right of the track.
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#58 Postby MGC » Fri Jul 07, 2006 10:25 pm

I was in Charleston a few months after Hugo courtesy of the US Navy. Being curious of the damage, I drove all over the Charleston area observing the damage. Damage in Charleston seemed typical of a cat-1/2 hurricane winds. Across the river, wind damage increased the further north on Hwy 17 one went. Lots and lots of trees snapped. I'd say solid Cat-3 with perhaps a few areas of low end Cat-4. Of course this damage was likely caused by gusts. No way was the wind damage as bad as I witnessed in Camille though. I drove out to Sullivan Island and the Isle of Palms to look at the water damage. Though significant, the surge damage didn't come close to Katrina or Camille. Hugo may have been a strong Cat-4 at landfall but I doubt it was a 5, I just didn't see any damage that was consistent with the other Cat-5 (Camille) that I have observed. The main reason the damage from Hugo was so low was because the strongest wind field occurred over the national forest, a sparsely populated region........MGC
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#59 Postby Derek Ortt » Fri Jul 07, 2006 10:28 pm

any cat 5 winds were well nroth of Charleston, about 40 miles or so
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#60 Postby MGC » Fri Jul 07, 2006 10:32 pm

That is true Dereck, the main area of wind damage was up the coast from Charleston. Tons and tons of pine trees snapped like sticks. Hugo deepened rapidly as the hurricane approached the SC coast, so much for the theory that major hurricane can't intensify over the continental shelf. Though rare I doubt this hurricane was a not an unusual occurrence for this area. I think Cat-4's are possible all the way to Cape Hatteras.....MGC
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