Cat 4 hurricanes very unlikely north of Florida on E Coast

[Matt-hurricanewatcher]

Hugo was a cat5 northeast of the leewards. If this is upgraded to cat5 at landfall that would mean it was the 4th cat5 to hit the US.

[marcane_1973]

I lived in Myrtle Beach when Hugo hit and we were a good distance away from the center and it scared the crap out of everybody especially the ones who never experienced a hurricane before that were moving down from up north. Trees snapping all night. I walked down to the oceanfront from Surfside Bch. 3 days after they finally let us in. The storm surge was huge being that far from the center. The surge came in as far as several blocks in most locations. That was crazy being a bit far from the center even though we were on the worst side. Hell even as far north as Wilmington got surge and damage as well. The biggest problem with Hugo was that it was moving so fast and intensifying at the same time not to mention a ton of tornadoes with this monster. That is the worst scenario. It was a high cat 4 on the scale easily. Hugo was a enormous storm that covered South and North Carolina and it sucked bigtime hitting late at night. Is it not the worst being in a major hurricane at night. You cant see anything and your just wondering if a tornado is gonna drop right on you. It always seems the worst hurricanes hit at night don't they.

[Jim Cantore]

Well I wish Katrina would have "fallen apart" a little more for the sake of the Gulf Coast residents.

Actually, even if Katrina had weakened to a Category One or Category Two before landfall, it would have still made little difference. It would have still carried a huge wind swath, destructive Category One/tropical storm-force winds, and would still bring in a tremendous surge.

Disagree. If it had weakened all the way to a Cat 1 or 2 instead of borderline Cat-4, there would have been a much smaller surge. It would have made a HUGE difference, IMO, as the wind field, while still large, would have been weaker.

Surge goes down alot slower then wind, here are examples

Isabel: Cat 5 3.5 days before landfall, still held a 10-12 foot surge at 105mph, normally associated with a cat 3.

Ivan: Cat 5 2 days before landfall. Weakened to 120mph, surge was 14-17 feet, normally associated with a category 4 storm.

Rita: cat 5 2 days before landfall, weakens to 115mph and produces a 18-20 foot surge, normally associated with a category 5 Hurricane.

Something those 3 storms had in common, was that they were large Hurricanes, only Isabel had a wider area of TS winds then Katrina, but Katrina had wider Hurricane Force winds then all of them

If Katrina weakened to say 90mph, I'd estimate a surge still around 18-22 feet, and still alot of damage, however not nearly as much to New Orleans.

[Audrey2Katrina]

Actually, you do not add a hurricane's forward speed to the winds on the right side.

Actually it was not >I< who was doing that, I was citing Mr. Ortt's logic in doing so. Frankly we are in agreement on this point--which would make the suggested windspeeds of Hugo NOT the 50 mph higher that has been suggested.

Audrey, you're justa tad bit mistaken here

perhaps I am, and perhaps I'm not... speculation does allow for wiggle room.

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)

Well that's all very interesting but to say that if we go up 50 mb we can jump from 80-90% country all the way to 100%, while a possibility, is not and cannot be beyond any doubt--especially looking back 17 years into the past. Basing our conclusion on what surface winds "might have been" using measurements at 12,000 ft can only be conjecture--granted educated conjecture, but conjecture all the same--there simply is no way to be certain. I'm sure the mets who handled Hugo were just as familiar with the data to which you refer--they just don't agree with your conclusion, and I would have to concur with that disagreement.

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

I'm not using pressure to "equate" to a wind speed, but the correlation is beyond dispute as there can be little doubt that it's a pressure gradient that creates those very winds. I'm glad you brought up Iris, though, as it very nicely supports exactly what I've been attempting to illustrate. It's lowest pressure was only about 12-15 mb higher than Hugo's, it's top winds around 140 mph but it's SIZE was akin to a Camille inasmuch as it was "tightly" wound and small. Satellite imagery I've seen of Iris show it MUCH smaller than either Katrina or Hugo, hence creating a much steeper pressure gradient, and THAT would account for higher wind speeds. In the case of Hugo you have a storm only about 15 mb lower, but spread out over an immeasurably larger radius, creating a much wider and less steep gradient, and THAT, I am convinced, would affect the wind speeds. Given similar sizes of Hugo and Katrina, the 14-20 mb lower pressure of Katrina, would have, if anything, created a deeper gradient and THAT is my point... not just a mention of central pressure. Additionally, while a baroclinic front was approaching, as Katrina was approaching landfall, it was no more "baroclinic" than Hugo... as satellite imagery of Hugo clearly shows a similar approaching front that picked it up and even an AMS article cites: "Over the eastern Atlantic, with better data coverage, the performance of the dynamic models began to improve, and once Hugo began to interact with the baroclinic zone over the United States, the dynamic models showed marked superiority." In other words: Non-Sequitur. And FINALLY, on this issue of a 934 mb storm "easily" supporting a Cat 5 status, please cite me one instance of a Cat 5 AT pressures above 934--just one. I'm not trying to be sarcastic, I'd just really like to see one such instance, which should be easy to find if it could "easily" support Cat 5 winds at that pressure, and I just can't seem to find one instance where it does--I defer to your much wider data base to enlighten me.

Now, let me “try” to show you how one can play conjecture with the numbers to come up with whatever contention they may wish to make about a hurricane. (*disclaimer: this is NOT being presented in any other light than to illustrate a point--not with the intent of presenting any further discussion on a much beaten dead horse)

1.) Highest winds recorded as “official” by the NHC for Katrina at Grand Isle were right at 90 mph 1 minute sustained, before instrument failure…that’s at 1000 Z, or nearly 2 hours BEFORE landfall. One “could” logically assume that winds would have risen for the next 2 hours until the storms COC had actually passed Grand Isle, and a figure of at least another 20 mph would be very plausible, if not probable.
2.) Now with sustained winds of 110 mph, bear in mind that Grand Isle, like Charleston, was on the SW, (or “weak”) side of the storm which actually made its landfall more than 20 nm to the east at Buras, La. Given a forward motion working “against” the storm <using a contention you first suggested, not I> due to it’s speed of approx 15 mph once it passed Grand Isle, that would, using similar logic, mean that top winds surely “should” have been at least 30 mph higher than that taking into account the forward motion of the storm, AND the fact that the NE would almost surely have had winds even faster than what Grand Isle had, this translates to a sustained wind at Buras of approx. 140 at the minimum, and possibly over 145 mph.

Now that’s using EXACTLY the same logic you employed with regard to ground measurements in arriving at your calculations for wind speeds for Hugo: 1.) winds measured on the SW “weak” side, 2.) the forward motion of the storm subtracts from the SW, but ADDS to the NE by the same factor. This has nothing to do with actual measurements as everyone knows all “official” instrumentation failed; but it DOES employ the same algorithm applied for Hugo’s landfall.

The bottom line, there is not now, nor has there ever been, an “infallible” algorithm (if there ever will be one) for calculation of wind speeds from a specified flight altitude to surface—saying it’s 95-100% here, but 90% there, and only 80% here without ANY room for error... too many variables. Same with the 1 minute sustained to peak gust. In justifying lowered numbers I find many march lockstep in using the higher 1.4-1.6 ratio to downplay sustained winds that they are convinced were not higher than the figures they claim, and yet I’ve noted that in going over most of the sustained to peak ratio on NHC’s own data that the ratio is as frequently closer to the 1.2 and 1.3, as it is the 1.4, and almost NEVER 1.6.
So what does all this prove? Nothing. It never does!

Those who want to believe Hugo was a 4 or 5 will do so, and their conclusions have just as much validity as anyone else’s in the absence of proof positive. Yes you can throw out a mathematical calculation hither and yon, and use a rule of “averages” to claim greater validity; however this in no way is the same thing as having proved anything. When arguing in a vacuum, neither side is going to win as there is no “air” there!

I stand firmly on the aforementioned position that Hugo wasn’t even remotely a category 5 at landfall.. and no amount of number-crunching will change that opinion--all due respect to those who disagree.

If I might ask a question: What would you say the top wind speeds of a storm like Katrina might have had as a highest likely gust, say, 300-400 ft. above the surface around second landfall--near the Bay St. Louis side (NE)... using all these figures what might you expect a maximum possible wind gust to be at that height? Presuming it's right "after" second landfall.

A2K

[Audrey2Katrina]

Hugo was a cat5 northeast of the leewards. If this is upgraded to cat5 at landfall that would mean it was the 4th cat5 to hit the US.

I VERY seriously doubt this is going to happen.

A2K

[Audrey2Katrina]

so much for the theory that major hurricane can't intensify over the continental shelf.

Excellent point... and this is what? 3-4 degrees or more further N. in Latitude as well.

A2K

[Derek Ortt]

Hugo did not intensify over the shelf, it did so over the GS and maintained over the shelf due to its very rapid translational speed

Also, my point about the winds was out of context. Hugo likely was in reality, 115KT, but the forward speed enhanced the winds to the north of the center in McClellanville, and decreased the winds in Charleston. That would yield the much weaker winds in Charleston and the 4/5 winds north of the city

[wxman57]

Surge goes down alot slower then wind, here are examples

Isabel: Cat 5 3.5 days before landfall, still held a 10-12 foot surge at 105mph, normally associated with a cat 3.

Ivan: Cat 5 2 days before landfall. Weakened to 120mph, surge was 14-17 feet, normally associated with a category 4 storm.

Rita: cat 5 2 days before landfall, weakens to 115mph and produces a 18-20 foot surge, normally associated with a category 5 Hurricane.

Something those 3 storms had in common, was that they were large Hurricanes, only Isabel had a wider area of TS winds then Katrina, but Katrina had wider Hurricane Force winds then all of them

If Katrina weakened to say 90mph, I'd estimate a surge still around 18-22 feet, and still alot of damage, however not nearly as much to New Orleans.

Hurricane Floyd,

Those 3 examples are not of a hurricane "holding" its storm surge. They are examples demonstrating that a hurricane with an unusually large area of maximum winds will produce a storm surge that may be considerably higher than for an average sized hurricane.

Also, Katrina hit in exactly the "right" place to produce the maximum storm surge. Where Katrina made landfall, the storm surge multiplier would be 1.75 times. The surge multiplier where Rita's strongest winds came ashore was about 1.4 times. It was those two factors combined with an unusually large area of maximum winds which produced the large surge. The peak intensity over a small area of the hurricnae when its out to sea is not a major factor in storm surge height at the coast.

Now, one thing that Ivan, Katrina, and Rita also had in common offshore was that they produced unusually large "trapped fetch waves" (also called "dynamic fetch waves"). I spoke with the author of a number of articles on trapped fetch waves at the last NHC in New Orleans (Allan MacAfee). He sent me a copy of a program to calculate these wave heights.

http://meted.ucar.edu/marine/mod2_wlc_gen/print.htm#36

You have to know a bit about wave generation to understand the concept. Basically, as I mentioned in a previous post, wave height depends on 3 basic factors - wind fetch (distance over which wind of the same average speed blows), wind duration (time that the wind blows over this fetch), and the average wind speed. Hurricanes (and other cyclones) are moving systems, so associated wave heights are generally duration-limited.

But here's the catch -- a wave moves at a velocity roughly equal to twice its period (time from crest to crest or trof to trof as it passes a point). Smaller waves have a lower period than larger waves. As waves in a hurricane build (generally right of the track is where the largest waves are), they move at a greater and greater forward speed. However, if the hurricane begins to accelerate to match the forward speed of the waves, then this can significnatly increase the amount of time that a given wind field blows across a given wind fetch. And since the waves in this fetch box are already very large, what you have is a greatly increased wind duration across this fetch. This is precisely what happened with Ivan, Katrina, and Rita, and that's at least partially why they generated 70-90 foot waves in the deepwater areas. And that's what produced all the damage to the offshore platforms.

So you would be partially correct in sayin that these 3 hurricanes produced very large waves offshore and that these waves may have added to the coastal damage. But the peak (cat 4-5) winds in Ivan, Katrina, and Rita were over such a small area (wind fetch) that these wind fields did not contribute significantly to the overall wave heights. It was still the large area of 70-120 mph winds that produced the extreme wave heights. Even without being a Cat 4 or 5 hurricane, Ivan, Katrina, and Rita would have still generated nearly the same wave heights because of their large area of high winds.

In summary, forget Saffir-Simpson based storm surge estimates, they're worthless. Coastal topography (just offshore) and areal coverage of a hurricane's hurricane-force winds are much more significant in storm surge generation than its peak wind field that covers generally a very small area near the eye.

[storms in NC]

A cat 5 can not hold itself for more than 30 -36 hours it only goes down to a cat 4. It can build back up to a cat 5 as we have seen last year. But only goes back down. For this days and times I wouldn't put it passed any thing. to happen anywhere

[baygirl_1]

I really appreciate the lessons here--- learning a lot! May I ask a question? The concept of a large wind field generating greater storm surge is intriguing. That makes sense to me, especially after Opal weakened yet still caused a terrible surge at my sister's home in the Fort Walton Area. I just am wondering how Camille fits into this. She was a relatively small storm, right? Yet, she created a pretty big storm surge for Mississippi. She was the benchmark for them before last year. I appreciate any info y'all can share about this.

[Derek Ortt]

Camielle being a small storm is a myth. It was actually slightly above average.

It was considered small when compared to a hurricane like Carla, but would be large when compared to Andrew

[wxman57]

Camille being a small storm is a myth. It was actually slightly above average.


It was considered small when compared to a hurricane like Carla, but would be large when compared to Andrew

Yep, that's true. And Camille hit the same bad spot that Katrina did, where the shoaling effect increases the storm surge to nearly double.

[Scorpion]

With Camille, how did New Orleans not get heavily damaged? Looking at the best track, it came almost as close to NO as Katrina did.

[wxman57]

With Camille, how did New Orleans not get heavily damaged? Looking at the best track, it came almost as close to NO as Katrina did.

Camille hit nearly the same point as Katrina, but it approached the coast from the southeast rather than from the south. This greatly reduced the storm surge west of the track.

[Extremeweatherguy]

None of the pictures or accounts I have found online show Hugo as being anything more than a borderline Cat. 3/4 storm.

http://webs.wofford.edu/cainam/journal%209-%20hugo.htm

http://www.publicaffairs.noaa.gov/photos/1989hugo.gif
^^wind map made for Hugo. This map shows that winds no higher than 110-120mph sustained were felt (even at the coast). From the Hurricane research division.^^

[Scorpion]

I personally believe Hugo was 125 kts at landfall.

[Hyperstorm]

Audrey2Katrina...

You want one instance when a Category 5 had a pressure above 934 mb?

There you have it... and in very recent times:

ZCZC MIATCPAT3 ALL
TTAA00 KNHC DDHHMM
BULLETIN
HURRICANE ISABEL ADVISORY NUMBER 33
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM AST SUN SEP 14 2003

...TENACIOUS ISABEL REFUSES TO WEAKEN...CONTINUES WITH 160 MPH
WINDS...

AT 5 AM AST...0900Z...THE CENTER OF HURRICANE ISABEL WAS LOCATED
NEAR LATITUDE 23.3 NORTH...LONGITUDE 65.2 WEST OR ABOUT 340
MILES...545 KM...NORTH OF SAN JUAN PUERTO RICO.

ISABEL IS MOVING TOWARD THE WEST-NORTHWEST NEAR 13 MPH ...20 KM/HR.
THIS MOTION IS EXPECTED TO CONTINUE DURING THE NEXT 24 HOURS.

MAXIMUM SUSTAINED WINDS ARE NEAR 160 MPH...260 KM/HR...WITH HIGHER
GUSTS. LITTLE CHANGE IN STRENGTH IS FORECAST DURING THE NEXT
24 HOURS.

HURRICANE FORCE WINDS EXTEND OUTWARD UP TO 85 MILES...140 KM...
FROM THE CENTER...AND TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP
TO 200 MILES...325 KM.

MINIMUM CENTRAL PRESSURE REPORTED BY A RECONNAISSANCE AIRCRAFT WAS
938 MB...27.70 INCHES.

LARGE OCEAN SWELLS AND DANGEROUS SURF CONDITIONS ARE LIKELY OVER
PORTIONS OF THE LEEWARD ISLANDS...THE VIRGIN ISLANDS...PUERTO RICO
...AND THE DOMINICAN REPUBLIC OVER THE NEXT FEW DAYS. THESE
DANGEROUS SURF CONDITIONS WILL ALSO AFFECT PORTIONS OF THE
SOUTHEASTERN U.S. COAST DURING THE NEXT SEVERAL DAYS.

REPEATING THE 5 AM AST POSITION...23.3 N... 65.2 W. MOVEMENT
TOWARD...WEST-NORTHWEST NEAR 13 MPH. MAXIMUM SUSTAINED WINDS...160
MPH. MINIMUM CENTRAL PRESSURE... 938 MB.

THE NEXT ADVISORY WILL BE ISSUED BY THE NATIONAL HURRICANE CENTER AT
11 AM AST.

FORECASTER AVILA

While I don't want to get into the debate regarding Hugo's landfall intensity without having studied all data, this proves that there can be huge disparities in a wind-pressure relationship.

[KWT]

hurricane Allen as well had a pressure apprently of 945mbs while still having winds of 140kts according tothe data I've seen and I'm willing to bet there are others as well apart from Allen and Isabel.

Mitch was a cat-5 at 933mbs, Anita was one at 931mbs, hurricane Edith was a cat-5 at a high 943mbs. Emily was a cat-5 at 929mbs which also isn't exactly low!

I won't go no furtrher back then as data starts to become a little shakey but as you can say actually there are quite a few hurricanes are what some would think on the high side of cat-5 status. While I'm not saying Hugo was a cat-5 at landflal, I'm just showing that actually there are at least 3 hurricanes that were above 938mbs and several others above 930mbs.

[Budro999]

Having lived in Charleston when Hugo hit, I can easily say that metro Charleston did not see Category 4 conditions at landfall. However, the Category 2 conditions experienced made for a terrifying night. Within a few months after the storm making landfall, I had the chance to go to Awendaw and McClellanville(two towns square in the NE quadrant of the hurricane at landfall). While the surge in those two areas was tremendous and caused immense damage, the type of wind damage I remember seeing would not have been comparable to a Category 5 storm. Yes, maybe in reanalysis, Hugo's max winds will be raised; however, I don't believe Category 5 status is warranted in this situation. Someone quoted a 12,000 foot flight level wind of 141 kts right before landfall, but I think we would need to see winds at other levels to see if the reductions from those levels provide comparable surface wind estimates.

There is another reason why I don't believe Hugo should ever be labelled a Category 5 storm, however. People in Charleston to this day believe they experienced Category 4 conditions the night of Hugo, when most only saw sustained cat 2 conditions. If you tell people there now that Hugo was actually a 5, fewer people will evacuate because they will tell themselves that they comfortably withstood a cat 5 storm, so why should they evacuate. It is the difference between perception and reality, and perception almost always is more powerful in these types of situations. A reclassification to Category 5 could actually cost more lives down the road when future hurricanes threaten the SC coast.

Finally, given what we now know about reduction factors, has anyone given thought to just how many storms will have significant changes to wind speed in reanalysis? One can imagine that the number will be significant.

[mountainspring]

I have a question. Is there any serious move afoot to recategorize Hugo as a Cat 5 at landing? I haven't heard of any but I may have totally missed it. Or is is just wishful thinking of a few peopel on the board?