“Category 6,” Hypercanes, Storm Warnings, and a Preview

I’m a subscriber to The Atlantic because, although I don’t agree with all the views of every writer, I deeply respect the fact that the magazine publishes pieces from all thoughtful and reasonable points of view. I think it’s good for all of us to be forced sometimes to question our priors by exposure to different opinions that are well-thought-out, well-argued, and evidentially defensible.

The February 2024 issue includes a piece about the notion of changing the Saffir-Simpson Hurricane Scale to add a “Category 6” rating for storms with sustained winds higher than 192 mph. In defense of this position, it’s not a journalist or a fiction writer with no background in the field proposing it. It’s the suggestion of a scientific paper by atmospheric scientists.

That said, I respectfully disagree with the idea. There are two reasons for that.

First is the issue that if a “Category 6” is added, that lessens the psychological impact of “Category 5.” We see this with Category 5 hurricanes that get downgraded to 4 before landfall. The National Hurricane Center doesn’t seem to want to do it even when the data supports it, and I understand why! When it does make such a downgrade, it’s often to a speed higher than the storm probably has at the time – 150 or 155 mph, the upper end of Category 4 – and the NHC products almost always include language about how those in the landfall zone should not focus on category because the storm remains extremely powerful, and so on. The hurricane forecasters seem to be well aware of the fact that people will not take a Category 4 as seriously as a Category 5, even if the difference is a matter of 10 mph. Adding a Category 6 will present the same problem.

But the second, and more serious issue, is that… well… I think my profession is far too optimistic about their own ability to change people’s behavior. I admit there is historical support for us to believe that we can do that. We’ve done it before! There was a time when better warnings did make a difference in people’s responses, and the death tolls of hurricanes and tornadoes fell sharply as a result of better science and better public awareness of what to do. The problem is that I think and fear that that time has passed. I think the greater problem we’re facing now is not lack of access to good information (by which I mean accurate and useful warnings). I’m sure that happens, but I think the bigger problem now is the choice too many people make not to believe what they are told.

Trust in science has absolutely cratered. This has been well-documented in surveys of the subject. Americans, at least, basically don’t trust anyone or anything anymore except whatever sources and institutions they consider to be aligned with their political views (and yes, this is about political views, not religious ones). I won’t go into the reasons. I have my own thoughts, and they’re grim indeed. In short, I don’t think this is the fault of atmospheric scientists either. (In some fields, IMO, scientists do bear partial blame. The replication crisis in psychology, for instance. Nutritional science also is culpable, since people notice when dietary advice – such as for saturated fats, special diets, and so on – is issued, widely disseminated, people are scolded and frightened about what they eat, and then the field discovers it was largely wrong and does a “mea culpa, our bad.” And that happens a lot.)

But outside those special situations, scientific consensus is actually pretty robust and stable. Atmospheric science is one of the fields where this is the case. Yet trust is declining for it too, and I think that what’s going on here is that a great many people choose to believe sources that lie and mislead them, because they have adopted a conspiracy mindset. In the case of atmospheric science, it’s the conspiracy theory that climate change is a “hoax” or “exaggerated,” and that the entire field, including meteorologists who forecast the day-to-day weather (and certainly NOAA, including the NHC, which are part of the “deep state” to these kinds of people) are in on it too.

We saw this with COVID: people who would die rather than take the vaccine because they believed outlandish conspiracies about the vaccine, and proved it in droves by dying. If this is what’s going on with people disregarding storm warnings, “better and more descriptive warnings” won’t fix that. I don’t see this possibility addressed much in literature about how to “improve warning responses.” This literature remains, for the most part, very hopeful, with little questioning of the premise that the problem is access to good information. Perhaps the reason is that the alternative – people have access to good enough information and are choosing not to believe it – is just too dark to consider.

In any case, for these reasons, I don’t support adding more categories. True hurricanes (the only kind we’ve seen… thus far) may occasionally hit 192 mph, the proposed “Category 6” cutoff. But they don’t usually make landfall at that speed. There are reasons for that: It’s not easy for a storm to maintain such an intensity when half of it is over land, and that is what “landfall” requires. The center of the hurricane’s eye must cross over land for landfall to be declared, which means half the storm has already come inland. (Some hurricanes are asymmetrical, with eyes skewed to one side or the other, because of shear. But these storms do not reach Category 5 intensity. A Category 5 hurricane is going to be almost perfectly symmetric and the eye will be in the center.)

I should clarify, I suppose, that it is not easy for a storm to maintain Category 5 intensity at landfall while its thermodynamic processes are typical.

On that note, what I think we may someday face is far worse: a theoretical kind of storm that has different internal processes for dissipating heat, because it has to. Hurricanes and tropical storms dissipate by moisture transport and venting. They draw heat from the sea surface (which is why they need warm waters) and vent it up and out. Or the heat is dissipated through rainfall and near-surface moisture fluxes. The temperature differential between the sea surface and the lower stratosphere/upper troposphere is what determines the storm’s maximum potential intensity.

But the equations of storm development predict that there are possible conditions in which a storm could not release heat fast enough: The sea surface would be too warm, and/or the upper troposphere too cold, for the energy that the storm pulls in to be dissipated by the usual means. In climate change, the seas would get warmer and the tropopause would get colder (more heat trapped at thicker levels of the atmosphere and less radiated outward into space). These storms would undergo runaway intensification to truly unbelievable intensities. They would eventually dissipate, but they would have to use internal frictional dissipation to do so. That’s slower, so they stay intense longer. And by intense, I mean intensities that are as-yet unheard-of.

These storms would be called hypercanes. This name was coined by Dr. Kerry Emanuel, and it refers not to the intensity of the storm, but the means that it uses to dissipate heat from the sea surface. Intensity is incidental to that, though their internal processes would physically necessitate extreme intensities. Under typical terrestrial conditions of upper-tropospheric temperature, hypercanes would have 700 mb internal pressure or lower.

There is, admittedly, a grey area between “typical” Category 5 hurricanes and hypercanes. There could be super-strong hurricanes that do dissipate heat by venting rather than friction. There is a wide range of potential intensities for them. Let’s say 192 mph, since that’s been proposed, up to the hypercane baseline. Since the definition of a hypercane is based on which thermodynamic processes are most important for its heat release, rather than what its winds are, this baseline is hazy. But there have been model runs of standard hurricanes with 250 mph winds:

(The above image does not depict a storm intensity that actually occurred. It was a model projection that turned out wrong. But it shows that dynamic equation-based models don’t break down at this intensity. Tropical cyclone thermodynamic processes still work out without the need for special physics schemes in the code to handle hypercane processes. There have been other models of such extreme hurricanes. See, for instance, Lin and Emanuel 2015, “Grey swan tropical cyclones” in Nature Climate Change. This paper describes, among other possibilities, a 233-mph/829.6 mb hurricane in the Gulf of Mexico and a 256 mph/784.2 mb one in the Persian Gulf. These are not modeled with hypercane processes, but are “merely” extreme hurricanes. The point is that the models can predict them. On Earth, hypercane processes don’t kick in at these intensities, extreme though they are.)

Hypercanes probably would begin at about 300-350 mph sustained winds, but again, their intensity would be incidental: an emergent phenomenon of how they had to dissipate heat intake, and the fact that it would be slower and therefore the storm had undergone runaway intensification. If a storm goes hypercane, I don’t think it should even be classified with categories meant to refer to hurricanes, since its internal processes would be different. But that’s still a range of over 100 mph for this hypothetical “Category 6.” Let’s suppose we started to see more storms in this range. Should we differentiate between those with 192 mph winds (or 200, for the sake of rounding) and those with 260?

But to return to the issue that I think we’re actually facing with warnings… I don’t think it’s a problem with information accuracy or availability. I think it’s a problem with trust of scientific authorities and stupid choices a lot of people make about whom to believe, not because they lack access to good sources, but because they choose to believe bad ones when those bad ones are part of their “tribe” or “team.”

And I don’t think there is a thing that scientists can do about it.

Epidemiologists couldn’t, after all.

I am going to address this (rather cynical and misanthropic) theme in my forthcoming novel, “The Inheritors.”

And yes, it’ll feature the whole “Category 6” debate.

And a hypercane.