Should there be a Category 6, or even a Category 7, to classify extra bit tropical cyclones like Haiyan?

Some tropical cyclones labeled Category 5 are much stronger than others. It has been suggested that we would be smart to extend the system to have a Category 6 and maybe even a Category 7 to allow the additional severity of these storms to be indicated when they are being spoken of in the news or by officials in charge of scaring people into doing the right thing, like running away or staying indoors.

There is resistance to this proposal that comes from two mostly distinct places. One is the community of those who deny the science of climate change, or climate change itself, or science itself. Their motivation is to not allow the so called “alarmists” (those who are alarmed at the changes happening on our planet) to have a tool to point out that severe weather can be very severe indeed. The other is the subset of meteorologists who are actually correct, in a way, when they point out that the Saffir Simpson scale, the scale with the five categories, can’t be extended because of the way it is built, but who are very incorrect, I think, when they point out that extending the scale would damage the most important available tool for scaring people into running away (or staying indoors).

The reason the Saffir Simpson scale can’t be extended is this. The scale has five categories of hurricanes. The first category, Category 1, is the category a hurricane that is at or near the minimum level of strength can be and still be called a hurricane. The top category, Category 5, is the level of strength at which a hurricane flattens a wood-frame suburban American neighborhood and takes out the overhead utilities to the extent that nearly full replacement, not just putting up a few new lines, is required. In other words, from the point of view of the vast majority of Americans living in regular homes or townhouses around the country, a Category 5 hurricane is total destruction of your way of life. You have to move, rebuild, live in a FEMA trailer for a while, etc. From the point of view of the citizen, the rescue workers and first responders, the parts of the government that are in charge of taking care of the refugees, and the meteorologists who discuss these things on the TV, a Category 5 hurricane is effective at the top category because it is as bad as it gets.

I would like to point out three reasons that this is wrong. I’m not actually going to suggest that we replace the Saffir Simpson scale with a different measure. Rather, I’m going to suggest that we add new measures and use them (there already are other ways to measure hurricanes).

The first thing that is wrong is that people are already stupid about hurricanes. The meteorologists don’t want to make a Category 6 or 7 because they don’t want a Category 5, which is total destruction of your American Dream, to look smaller. They want Category 5 to look extra bad because it is, in fact, about as bad as it gets. However, people already don’t get Category 5. For one thing, people think that a hurricane “arrives” when it makes landfall. This landfall thing is a thing Meteorologists use. This is when the eye reaches the shoreline. There are important meteorological things that happen when the eye reaches the shoreline and it is highly convenient and very polite of these monster storms to have something that serves as a virtual point on the map indicating their center so we don’t have to have an endless debate about when the storm “arrives.” But if you are sitting there on the coastline thinking that the hurricane that is bearing down on you hasn’t gotten there yet when the eye is 20 miles away but 130 mph winds are taking off your roof and a storm surge has already broken the dike and all the escape routes are already flooded then you don’t understand that hurricanes are huge. And, I’ve seen meteorologists standing in the 100+ mph winds talking about how the hurricane has not arrived yet, and we’ve all seen the Bush administration claim that Katrina did not cause flooding in New Orleans because the flooding happened before the hurricane arrived, because she had not made landfall yet.

So, now we might say something like “a Category 3 hurricane will come ashore on the Louisiana-Mississippi border” and people who live a ways away have to be reminded “oh, and there will be hurricane force winds over there where you live too” as though this was a separate thing. Hurricanes are not eyes of hurricanes, and the wind field of a certain category of hurricane can very large or very small, and what you have to do because a hurricane is coming may be very unconnected to to simplified and incorrect conceptualization of the hurricane that the Saffir Simposon scale or the Storm Stud on the beach gives you.

On top of this, the Saffir Simpson scale refers only to maximum sustained wind, not the size of the wind field, the intensity of storm surge, or the location and extent of coastal flooding, or the rain and subsequent flooding which may depend on topography, and the tornadoes that spin off, etc. etc. It is only telling us one thing, telling it to us poorly, ignoring things that are more important, and ignoring the context of ignorance and confusion that surrounds these storms.

And speaking of ignorance, there is this: People misunderstand storms. Should a scale of measurement of a storm’s effects be designed to accommodate ignorance, or to accommodate the need to measure the storm’s effects?

Anyway, those are the first two reasons to not fetishize the Saffir Simpson scale. It is part of the ignorance, not an anecdote to it, and it ignores some of the most imprtant aspects of the storm, or at least, fails to correlate well with those things.

The third reason Saffir Simpson is sometimes problematic is because it is, explicitly, a level of destruction meter and it sometimes does a poor job at that. Notice that the number of miles per hour that the winds much reach to jump to the next category is not linear. Some of the categories are 19 mph ‘wide’ and some are 24 mph ‘wide.’ This is because Saffir Simpson categories are not wind speed categories no matter how much they look like they are. They use windspeed but they are categories of destructiveness. Here is the Saffir Simpson scale, officially, from the National Weather Service:

Category 1: Very dangerous winds will produce some damage: Well-constructed frame homes could have damage to roof, shingles, vinyl siding and gutters. Large branches of trees will snap and shallowly rooted trees may be toppled. Extensive damage to power lines and poles likely will result in power outages that could last a few to several days.

Category 2: Extremely dangerous winds will cause extensive damage: Well-constructed frame homes could sustain major roof and siding damage. Many shallowly rooted trees will be snapped or uprooted and block numerous roads. Near-total power loss is expected with outages that could last from several days to weeks.

Category 3: Devastating damage will occur: Well-built framed homes may incur major damage or removal of roof decking and gable ends. Many trees will be snapped or uprooted, blocking numerous roads. Electricity and water will be unavailable for several days to weeks after the storm passes.

Category 4: Catastrophic damage will occur: Well-built framed homes can sustain severe damage with loss of most of the roof structure and/or some exterior walls. Most trees will be snapped or uprooted and power poles downed. Fallen trees and power poles will isolate residential areas. Power outages will last weeks to possibly months. Most of the area will be uninhabitable for weeks or months.

Category 5: Catastrophic damage will occur: A high percentage of framed homes will be destroyed, with total roof failure and wall collapse. Fallen trees and power poles will isolate residential areas. Power outages will last for weeks to possibly months. Most of the area will be uninhabitable for weeks or months.

See how I did that without even mentioning wind speeds? Notice that these categories are levels of destruction mainly of human-made structures. Saffir and Simpson did not invent destruction. They did not invent wind speed. What they did was to list levels of destruction that make sense, like how bad the power outages will be or whether or not houses will get knocked down just here and there or everywhere, and how long after the disaster everything will be a mess. Then, Saffir and Simpson linked these categories of destruction to wind speed thresholds that do not form even categories. This is not a set of wind speed categories. This is a set of categories indicating levels of destruction that, of course, go up with more wind speed but not in a linear fashion.

I note that when asked about a Category 6 storm Simpson had this to say, quoted in Wikipedia:

According to Robert Simpson, there are no reasons for a Category 6 on the Saffir-Simpson Scale because it is designed to measure the potential damage of a hurricane to manmade structures. Stating that “…when you get up into winds in excess of 155 mph (249 km/h) you have enough damage if that extreme wind sustains itself for as much as six seconds on a building it’s going to cause rupturing damages that are serious no matter how well it’s engineered”

As brilliant as the Saffir Simpson scale is, there is a problem with categorizing levels of destruction beyond the fact that much of the destruction and death may be flooding which is not addressed directly by the system. A hurricane in a hilly third world country with a lot of erosion due to deforestation, and where people live in homes that can be blown down more easily, are not going to experience the same level of destruction as people who live in a first world country with the experience of a major typhoon and who rebuilt their homes to be concrete bunkers with storm shutters and excellent drainage systems in place (a friend of mine lives in a home on Osaka that is built like this; there was a major typhoon there years ago and this is how people there rebuilt). Saffir Simpson has its uses but these uses to not apply globally or across time as conditions change.

The reason people are asking about a new category is this: We may need a new baseline. This is true with climate change in general. If we normally get Category 1 through 5 storms and the 5’s are rare and only barely go over the line that defines a Category 5 storm on the Saffir Simpson scale, then we don’t need to change. But if there is an increasing number of storms that turn into super storms and go many tens of miles over the Category 5 line, as Haiyan did (with wind speeds of 195 mph, enough to make it a Category 6 or even 7, if we extended the scale) then we should acknowledge the shifting baseline by adding a category or changing the system.

I think we should keep Saffir Simpson because it is already in use, but add categories every 20 mph as needed. But in addition we should add or begin to use more of the other ways of measuring a hurricane, that indicate the overall strength and size of the beast. The general public might be too stupid, according to some, to handle even a tiny bit of complexity, but if you live in a hurricane prone area knowing that hurricanes have two or three pertinent characteristics is important and you better know that. Knowing what a given hurricane that is coming your way looks like is important and you better know that. Knowing that the total energy of a storm is X, the likely destructive force is Y (from a modified Saffir Simpson that has more categories), that you are in a zone of likely wind strength of Z and if you are on the coast likely storm surge of F sounds like an awful lot to know, but it is less information and less complicated than the following: