Katrina vs. Andrew (and Ivan, Lili, Rita) -- Size Matters!

[wxman57]

I think what's often lost in these discussions about whether or not Katrina or Rita were Cat 3s or 4s is that you just cannot compare one hurricane to another just based upon PEAK intensity. Case in point, Andrew vs. Katrina at landfall. Clearly, Katrina's peak winds were lower than Andrew's, but not by as much as the Cat 5 vs. Cat 3 argument would suggest.

Take a look at the HRD wind analysis below from Andrew side-by-side with one from Katrina. Note that Andrew's peak Cat 5 winds were only over a TINY area a few miles across. There are Cat 5s and there are Cat 5s. Clearly, Andrew was near the bottom of the scale of a Cat 5 in terms of both intensity AND coverage of Cat 5 winds.

Now look at Andrew's 75+ mph wind area vs. Katrina's. Even though Katrina is being considered a lower-end Cat 3 at landfall, look at how HUGE its 75+ mph 1 minute sustained wind field is compared to Andrew's. As I've said before, most hurricanes have a very small area of 75+ mph winds. It's these 75+ mph sustained 1-minute winds that do most of the damage to structures. And it's this large expanse of 75+ mph wind that produces the large storm surge - NOT the peak winds that occur in only a tiny part of most hurricanes.

Here's the graphic. I encircled the 75+ mph winds in white on both images. Katrina's 75+ mph wind field extended well off the right side of the graphic, all the way to the Alabama border. Now, I ask you - which would be the more devastating hurricane at landfall, the tiny but stronger (in one quadrant) Andrew or the massive Katrina with 3-4 times the areal coverage of hurricane-force and greater winds?

<img src="http://myweb.cableone.net/nolasue/AndrewvsKatrina.gif">

[senorpepr]

Ahh... PERFECT description! Thanks. This is a great visual to show that a weaker, bigger storm (like Katrina) can cause a lot more damage than a stronger, smaller storm (like Andrew).

It isn't so much the strength of the winds, but rather how long those winds last.

[wxman57]

To compare with another hurricane, let's look at Katrina vs. Ivan at landfall. Ivan was surely a HUGE hurricane compared to average, but it was in a weakening phase at landfall and those stronger winds were being elevated above the surfact. Note that Ivan is identified as a Cat 2 at landfall with 95 kt max winds in a tiny area. Katrina had a much larger area of hurricane force winds, and a very much larger area of 80-90 kt winds.

Now also consider that the coast where Katrina hit is VERY vulnerable to storm surge vs. where Ivan hit. For the Gulfport area westward, the surge multiplier factor is about 1.9 vs. about 1.0 to 1.1 in Pensacola. So the same storm hitting southwest Mississippi would produce almost twice as high a storm surge as one hitting Pensacola.

<img src="http://myweb.cableone.net/nolasue/KatrinavsIvan.gif">

[vbhoutex]

You have just illustrated perfectly what I stated in the Katrina wind analysis thread. The graphics are the key as well as the understanding that sustained winds over a longer period and a larger time will produce incredible damage even if they aren't CAT5 winds.

[wxman57]

Or Katrina vs. Lili at landfall. Note the TINY area of hurricane force winds in Lili at landfall. And many people think that they went through a hurricane when Lili passed over south-central Louisiana.

http://myweb.cableone.net/nolasue/KatrinavsLili.gif

[cjrciadt]

Or Katrina vs. Lili at landfall. Note the TINY area of hurricane force winds in Lili at landfall. And many people think that they went through a hurricane when Lili passed over south-central Louisiana.

<img src="http://myweb.cableone.net/nolasue/KatrinavsLili.gif">

No Comparsion thanks for showing us this wxman57

[wxman57]

And finally, Katrina vs. Rita. Note that even though Rita had just a TINY area of Cat 3 winds at landfall, it had a HUGE area of 75+ and 58+ mph winds that extended well inland. Many people in south Louisiana actually saw 75+ mph wind for the first time ever. It's that large 75+ mph wind area that produced the huge storm surge and the total devastation along the low-lying coast.

<img src="http://myweb.cableone.net/nolasue/KatrinavsRita.gif">

[Brent]

Thanks so much for this wxman.

*keeps thinking how lucky Miami was in 1992*

[Derek Ortt]

The H-wind of Andrew is old, I believe, as a new one published in Dunion, 2003 has 153KT, but over a very small area. At RSMAS, only marginal cat 3 winds were recorded, and that is just 20 miles north of the landfall location, and in the center of Miami, likely cat 1 (only Coconut Grove went through a major hurricane, not the Miami CBD or Miami Beach)

One thing about Katrina, the 85KT wind radii was also very large. These winds can cause total devastation, which is what ALL of Mississippi received

[Brent]

The H-wind of Andrew is old, I believe, as a new one published in Dunion, 2003 has 153KT, but over a very small area.

Geez... That's almost 180 mph...

[f5]

Katrina also had CAT 5 surge with it.while at the same time the media said it was weaking.well that made folks think since the winds are down the surge will be down also.before katrina the NHC showed those surge maps they decrease the surge potential since the winds came down.

[wxman57]

Katrina also had CAT 5 surge with it.while at the same time the media said it was weaking.well that made folks think since the winds are down the surge will be down also.before katrina the NHC showed those surge maps they decrease the surge potential since the winds came down.

More precisely, one might say that Katrina had a surge that would more typically be associated with a Cat 5 but was, indeed, produced by a very large Cat 3 hurricane. I think the problem here is that even though Katrina's peak winds were not at Cat 5 level, its area of hurricane-force and greater winds was extremely large. I calculate about 14,000 square nautical miles of 75+ mph winds as Katrina approached the coast. The SLOSH model, I believe, would use a value much lower than this for a typical Cat 3. In fact, the area of 75+ mph winds in Katrina would probably be larger than in a typical Cat 5.

[quandary]

Size matters, but doesn't that just affirm the theory that its pressure that causes the damage? Pressure either translates into really high winds (strong gradient) or a large area of weaker, but still destructive, winds (weak gradient). In either case, you get the same amount of damage as long as the winds move over areas of equal damage potential.

[artist]

thanks for posting that. really helps to understand.
CAn you tell me where I would find Jeanne's and Frances's windfield?

[senorpepr]

Size matters, but doesn't that just affirm the theory that its pressure that causes the damage? Pressure either translates into really high winds (strong gradient) or a large area of weaker, but still destructive, winds (weak gradient). In either case, you get the same amount of damage as long as the winds move over areas of equal damage potential.

No, pressure is just a part of the equation. P/r=gradient. The gradient, which directly translates to wind speed, is the driving factor in damage potential, with pressure and storm radius being the two parts in gradient.

Pressure alone is as responsible of damage as storm radius.

[f5]

wasn't Katrina's CAT 5 staus played a role in the surge vs one that was never a CAT 5?

[Derek Ortt]

the fact that it was a strong 4 when it first moved over the continental shelf is what caused the very high surge. The surge is more related to initial intensity of the storm when it moves over the shelf than it is the landfall intensity since the water is piled into the shelf waters once it moves onto the shelf

[john potter]

superb posts, wxman-- kinda settles some scores on that very interesting 37 part Katrina intensity thread (I loved every word of it, from the concise narratives of the pro-mets to the audaciousness of the passionate cat-fivers). Wxman, your posts show strikingly that the LA landfall pressure (918 mb) supported a much larger radius of cat 2 and 3 winds -- vs the argument that 918 mb MUST support cat 5 effects (the Bastardi argumewnt, I guess, is that higher winds must adjust --fill? --by vertical motion-- a 918 mb "vacuity"). My question is that when Katrina reached and kept its wide-eyed annular phase up to 17 hours before LA landfall, at 902 mb, did it have any cat 5r characteristics in its windfield? Was there enough instrumentation to do a good HRD analysis at that time? I mean Katrina was over open 91 degree (loop) water in a relatively friction free environment.

[Swimdude]

No bashing meant by this AT ALL... I just think it's craaaazy that we're now "talking down" towards Hurricane Andrew. Just the fact that something worse actually occured hasn't been fathomable in my lifetime.

[wxmann_91]

Looking at the HRD analysis, the windfield of hurricane-force winds inside Charley at landfall could fit into Katrina's eye at landfall.