Is the 5th category unnecessary?

[SconnieCane]

The categories 1-5 should be used for the amount of destruction a storm causes after the storm has passed. For example Katrina category 5 damage. So it should be labeled as a cat 5. Would you classify Allison as a category 5 tropical storm? I would, so this is how they should go about it.

This seems like a step backward, like the way tornadoes are measured on the Fujita/Enhanced Fujita scales by using damage as a proxy to estimate the intensity. With satellite estimates and recon, we have tools to estimate the intensity of tropical cyclones in real time (imperfect as they may be).

If I recall correctly, there are already methods/scales to better quantify the expected impacts of all hazards from a landfalling tropical cyclone (surge and freshwater flooding, in addition to wind), but none of them have really become universally accepted/official yet.

[abajan]

I must say this is different from the usual "Should we add a Cat6 to the list?" discussion.
But no, I don't think the 5th category is unnecessary. Cat5s should probably be described as extremely catastrophic, so as to distinguish them from Cat4s.

Perhaps it would be better to drop the term "hurricane", call everything from 39 mph up "tropical storms", and start the categorization from 39 mph. So, Cat1 and Cat2 could be used up to 73 mph, and Cat3 to Cat7 could replace the current Cat1 to Cat5. But I'm not a fan of tinkering with the categories at all, because doing so would only make it more difficult to compare the strengths of tropical cyclones of many years ago with those of today.

[Teban54]

I always find it interesting that the SSHWS has a notably greater gap between Cat 4 and Cat 5 than other categories:

Cat 1: 64 kts
Cat 2: 83 kts (+19)
Cat 3: 96 kts (+13)
Cat 4: 113 kts (+17)
Cat 5: 137 kts (+24)

This is also obvious when we consider how many multiples of 5 there are in each category (i.e. number of possible official intensity estimates):

Cat 1: 65, 70, 75, 80
Cat 2: 85, 90, 95
Cat 3: 100, 105, 110
Cat 4: 115, 120, 125, 130, 135
Cat 5: 140 and above

In other words, it's harder intensity-wise for a Cat 4 storm to hit Cat 5 than any other intensity jumps. Since the SSHWS is primarily based on wind damage, I think it the larger gap shows that
1) Cat 5 in SSHWS is defined based on extreme damage that is incredibly hard to achieve; and/or
2) At such high intensities, a much greater increase in wind speed is required to produce significantly greater wind damage.

Indeed, we can see that a low-end Cat 5 (like Michael) does produce much greater wind damage than a low-end Cat 4 (like Harvey). From that perspective, a Cat 5 is indeed necessary.
However, a high-end Cat 4 can often produce just as much damage as a low-end Cat 5. Iota's eyewall passed Providencia officially as a 135 kt Cat 4, but the tree damage there seem comparable to Michael. This is hardly unique to Cat 4/5 though - see Sally and Zeta.

Regarding the difference between peak intensity and landfall intensity as people pointed out: While Cat 3 landfalls are typically less damaging than Cat 4/5 landfalls, it seems to me that storms which peaked at Cat 5 and weakened to Cat 3 (like Katrina and Ivan) often deal more damage than storms making Cat 3 landfalls at peak intensity (like Zeta). Florence and Ike get honorable mentions.
Maybe it's because the former are typically larger due to eyewall replacement and pack more energy. Or maybe it's something else, I don't know. Regardless, it shows that peak intensity might have some correlation to damage, even if less than landfall intensity.

[InfernoFlameCat]

While there might be SOME difference between a Category VI and V, those differences are quite minor in the grand scheme of things. The fact that it is common for Category IV storms to cause as much damage and as many deaths as Category V storms should say something. What matters is the large-scale impacts, and there is not much difference in terms of large-scale impacts.

While one can argue a 155mph cat 4 is essentialy a cat 5 in damage, what about those 175mph + systems that absolutely destroy way more than any cat 4 could dream of on a wind scale. And then Dorian ripping apart concrete like it was an EF5 twister(gusts at 220mph) no cat 4 could do that (Olivia in the south near Australia was a freak storm gust so not regularly gusting that extreme) I mean just a huge difference.

[NotoSans]

SSWHS refers to damage caused by winds only. A tropical cyclone can be damaging due to its storm surge (which is the case for Katrina) and rain (which is the case for Harvey or even Florence) as well. One may argue that SSWHS is misleading in this sense, but the solution should be getting rid of the scale as a whole, rather than focusing on one single category.

Systems in the WPAC also provide support for maintaining the 5th category (if we stick with a scale measuring winds only). One can easily see the difference in wind damage brought by Haiyan (a high-end category 5) in the Philippines, Rammasun (a low-end category 5) in China, and Mujigae (a low-end category 4) in China.

[Nuno]

I must say this is different from the usual "Should we add a Cat6 to the list?" discussion.
But no, I don't think the 5th category is unnecessary. Cat5s should probably be described as extremely catastrophic, so as to distinguish them from Cat4s.

Perhaps it would be better to drop the term "hurricane", call everything from 39 mph up "tropical storms", and start the categorization from 39 mph. So, Cat1 and Cat2 could be used up to 73 mph, and Cat3 to Cat7 could replace the current Cat1 to Cat5. But I'm not a fan of tinkering with the categories at all, because doing so would only make it more difficult to compare the strengths of tropical cyclones of many years ago with those of today.

Truthfully, this is what makes the most sense. As we understand the nuance of cyclones better, we realize it's all a spectrum in which we arbitrarily decide to classify storms. Clearly even in this forum pro-mets are in constant disagreement with developing storms early in their lifespan. Minimal category ones usually don't have a complete eyewall, what is the deterministic difference operationally between that and a 60 kt tropical storm aside from the name which we use to describe it?

[beoumont]

For a number of years before the Saffir Simpson scale was used in advisories, when a hurricane reached 150 mph, NHC advisories stated "The Great Hurricane (Inez, 1966 for an example) is now located at -------------

[al78]

The SS scale is a very blunt estimate of the destruction potential of a storm which is useful for communities in its path. It should be noted that wind damage goes up non-linearly with wind speed, a power law relationship I think, so there is a significant difference between a very destructive category 4 where the buildings are badly damaged but can be rebuilt, and a devestating category 5 that can render an area uninhabitable for months. If a cat 5 is coming your way, it is like Ivan Drago in Rocky IV, "Whatever he hits, he destroys!" (https://www.youtube.com/watch?v=O1IkeV1mH-w).

The SS scale is a long way from perfect. It doesn't take into account storm surge or rainfall, which together historically have killed more people and destroyed more property than the wind, and it doesn't take into account the breadth of the storm which influences how long an area gets subjected to damaging winds. That is why there have been efforts to develop a better destruction potential scale, such as the Hurricane Severity Index (https://en.wikipedia.org/wiki/Hurricane_Severity_Index), which brings size into the picture, larger size hurricanes bring a bigger storm surge for the same wind speed.

[ouragans]

Is the 5th category unnecessary?

Absolutely NO

I must say this is different from the usual "Should we add a Cat6 to the list?" discussion.

True, but erasing a category is unproductive.

There is no comparison possible between 125 kts and 160 kts winds

[al78]

Regarding the difference between peak intensity and landfall intensity as people pointed out: While Cat 3 landfalls are typically less damaging than Cat 4/5 landfalls, it seems to me that storms which peaked at Cat 5 and weakened to Cat 3 (like Katrina and Ivan) often deal more damage than storms making Cat 3 landfalls at peak intensity (like Zeta).

I think in these two cases the high destruction for their landfall category was largely because of the large diameter of these hurricanes. Certainly in Katrina, the storm breadth was a huge factor in generating the huge storm surge, and the fact it was undergoing an eyewall replacement cycle on approach to land which broadened the hurricane force winds. The landfall location east of New Orleans was also optimal for northerly winds on the west side of the eyewall pushing water from lake Pontchartrain into the levees which ultimately failed catastrophically flooding New Orleans and sparking a humanitarian crisis. Ivan could have been much worse if it had made landfall a little further west and funnelled a storm surge up Mobile Bay. Opal (1995) is also a good example of a large weakening hurricane from a cat 5 peak which pushed a big storm surge onshore. Even a cat 1 or 2 can cause way more damage than its category would suggest if it is large in size, Ike and Sandy are examples. That is the main weakness of the SS scale, it only looks at wind, but it is water that has the biggest impact in a landfalling hurricane, compact storms like Charley and Andrew excepted.