STRONGER HURRICANES?: Some scientists wonder if a new category is needed to describe the strongest hurricanes.
Image: Courtesy of NOAA
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Atmospheric researchers tend to agree that tropical cyclones of unusual ferocity are coming this century, but the strange fact is that there is no consensus to date on the five-point scale used to classify the power of these anticipated storms. In what may sound like a page from the script of the rock-band spoof Spinal Tap with its reference to a beyond-loud electric guitar amplifier volume 11, there is actually talk of adding a sixth level to the current Saffir-Simpson hurricane scale, on which category 5 intensity means sustained winds higher than 155 miles per hour (250 kilometers per hour) for at least one minute, with no speed cap.
The lack of an upper limit on the scale results in all of the most intense tropical cyclones getting lumped together, despite their wide range of power. Category 5 becomes less descriptive when it includes 2005's Emily, which reached peak wind speeds of 257.5 kph (160 mph) and six hours in category 5; the same year's Katrina which held peak wind velocity of 280 kph (175 mph) for 18 hours in the category; and 1980's Allen, churning with peak winds at 305 kph (190 mph) maintained for 72 hours in the highest category.
And now the ferocity forecast for the century adds to this classification problem. "The severe hurricanes might actually become worse. We may have to invent a category 6," says David Enfield, a senior scientist at the University of Miami and former physical oceanographer at the U.S. National Oceanic and Atmospheric Administration (NOAA). This new level wouldn't be an arbitrary relabeling. Global satellite data from the past 40 years indicate that the net destructive potential of hurricanes has increased, and the strongest hurricanes are becoming more common—especially in the Atlantic. This trend could be related to warmer seas or it could simply be history repeating itself. Data gathered earlier than the 1970s, although unreliable, show cycles of quiet decades followed by active ones. The quiet '60s, '70s and '80s ended in 1995, the year that brought Felix and Opal, among others, and resulted in $13 billion in damages and more than 100 deaths in the U.S.
The pros and cons of categories: Five or six?
The average difference between the current categories equals nearly 20 mph, so a category 6 label would likely be applied to hurricanes with sustained winds over (280 kph) 175 mph. The speed and destruction of hypothetical "category 6" storms is speculative, despite the hurricanes with winds at that level.
After all, meteorologists and climate researchers may not even choose a category 5 storm from the record books if asked to identify the most powerful tropical cyclone in history, because the Saffir–Simpson scale fixates on maximum wind speed lasting for at least one minute and disregards the many other large-scale components that factor into a storm's level of devastation. The whole index should be thrown out the hurricane-proof window, some say.
"If I could do it, I would do away with categories," says Bill Read, director of NOAA's National Hurricane Center (NHC). "The whole indexing [of hurricanes] was done back in the '60s and '70s when we had no way to convey the variables of damage that the storm did. We didn't measure it that carefully; we didn't have the tools."
Even nowadays, instruments to measure actual wind speed are often destroyed during extreme storms, so estimates have to be extrapolated from satellite images and other data. Actual observations can also be suspect. It took 14 years for the World Meteorological Organization to acknowledge that an anemometer in Australia recorded a world record wind speed of 407 kph (253 mph) during Tropical Cyclone Olivia in 1996. Wind speed science has improved over the years. Since the 1990s direct wind measurements from hurricane-hunter aircraft have replaced central pressure measurements, which were often a proxy for wind speeds.
Variables used by meteorologists and climatologists to assess damage can go beyond wind speeds to include duration over land and the extent of deadly storm surges. Read sums it up this way: "Size matters: Katrina, Rita, Ike—all of them made landfall at a 2 or 3 level, but look at the damage they caused. Obviously a category did not accurately describe the impact."
A transition to "impact forecasting" began last year when NOAA's National Hurricane Center simplified the Saffir–Simpson hurricane scale and renamed it the Saffir–Simpson hurricane wind scale. This change involved stripping away the scale's former central pressure, flooding and storm surge estimates. These factors among others are now forecast separately. In 2009 the National Weather Service began using new probability models that provide storm surge estimates ranging from 0.6 to 7.6 meters (two to 25 feet).
What the future holds
History keeps us guessing about where and when the next big tropical cyclone will hit on the U.S. Atlantic or Gulf coasts. As for the most powerful hurricane ever, experts are divided. Some say 1998's Gilbert.; an official answer from a NOAA Web site lists three: 1969's Camille, 1980's Allen and 2005's Wilma (the World Meteorological Organization agrees with the latter).
William Gray, professor emeritus of atmospheric science at Colorado State University in Fort Collins and the "grandfather" of annual hurricane season forecasting, picked the category 4 Great Miami Hurricane of 1926. NHC Director Read went with an unnamed Caribbean hurricane from 1780.
The Atlantic hurricane season, which runs from June 1 to November 30 annually, is predicted to produce more and stronger storms than average this year, although active years have been the norm since 1995. That year the Atlantic entered a period of warm sea-surface temperatures of what is called the Atlantic Multi-Decadal Oscillation, and such cycles typically last two to three decades.
"If the future is like the past, we should have another 10 to 15 years of this active period," Gray says.
This oscillation means the Atlantic is expected to cool in the future, obscuring links among hurricane activity and global warming. Perhaps counterintuitively, recent computer modeling studies predict fewer tropical cyclones if the ocean heats up further as a result of global warming. But they also predict intensification of the ones that do form, albeit with limited confidence. Frequency drops by 6 to 34 percent this century, according to 2010 review article in Nature Geoscience, whereas intensity rises 2 to 11 percent. (Scientific American is part of Nature Publishing Group.)
Today, water is a bigger concern than the wind when it comes to property destruction and loss of life. Look for more emphasis on storm surges in future forecasts, because it is the main reason why evacuations become necessary. Many planners suggest following Read's prescription: "In the U.S. 'Run from the water, hide from the wind' is pretty good, simple advice."
As for the addition of a new category 6, Read insists it is not needed. "I'd be totally opposed to that, even if they did get stronger," he says. "I'll fight 'em tooth and nail under my regime. We'll keep what we have now, but I'm going to focus more on the impacts."
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27 Comments
Add CommentWhy arbitrarily stop at Cat 6?
Reply | Report Abuse | Link to this"As for the addition of a new category 6, Read insists it is not needed. "I'd be totally opposed to that, even if they did get stronger," he says. "I'll fight 'em tooth and nail under my regime."
What a pointless little bureaucrat.
Yes, this is exactly what we need; A hurricane that is "one louder".
Reply | Report Abuse | Link to thisAs a geologist we have the same issue with earthquake measurement. The scales used are somewhat meaningless as far as physical impact on the natural and social environments. There are so many variables involved that comparing the impact one earthquake to another 'on scale' is comparing apples and oranges.
Reply | Report Abuse | Link to thisWhy is there no measurement equipment that can survive high winds? Is it the debris flying around, or too-fast operation of a spinning-cup anemometer? So put them inside a welded steel re-bar cage to deflect debris, and use two flow meters, one free-spinning for say 0-150 mph with a maximum speed limiter, and one with slimy viscous braking designed for 125-400 mph.
Reply | Report Abuse | Link to thisCategory doesn't tell us a whole lot. Storm surge, size, and duration (speed) are the real indicators. One problem I do see, is that, over the last few decades, satellite data and hurricane hunter flights mean that more storms are named than in the past. At least two, possibly three or four, of this year's storms would not have been identified or named a few decades back. Best example is Cindy, the end of an old front, in the north Atlantic, and barely named before it dissapeared. This not only tends to inflate the numbers, but causes complacency, like crying wolf. When a realy serious storm does come, some people will be less likely to evacuate and cause more casualties.
Reply | Report Abuse | Link to thisI think the author, Mr.Harper did a nice job on this article. I felt informed in reading through it. Some links to the names of the hurricanes would be nice, but I can bear my imagined burden of searching NYT or wikipedia, or the Library of Congress.
Reply | Report Abuse | Link to thisI am amazed that natural wind speeds can get that high, and cannot imagine moving that fast through the air in a car, much less the debri that winds like that can carry.
You don't even know Bill Read. He's been a friend of mine for many years. As a hurricane expert myself, I can tell you that the Saffir-Simpson scale has done far more harm than good. Too many people base life-or-death decisions on the scale rather than listening to the actual forecasts for their area. Many coastal surge zones are still defined by Saffir-Simpson category, when a hurricane's maximum sustained wind isn't even a factor in the calculation of storm surge. I agree with Bill, the Saffir-Simpson scale has outlived any possible usefulness.
Reply | Report Abuse | Link to thisThe idea of a category 6 storm reminds me of that famous scene from "This is Spinal Tap"
Reply | Report Abuse | Link to thishttp://www.youtube.com/watch?v=ll7rWiY5obI
We are now facing the prospects of an unpredictable storm forecast for the US east coast just days after our 5.8 earthquake that was felt in 22 states.
Reply | Report Abuse | Link to thisI know that now I am paying more attention to predicted rain fall rates, storm surge hight and footprint, wind speeds, tracking speeds, and such; and I am paying less attention to the presumed changes in categories. Certainly the intensity is useful in knowing it will get stronger and then weaken before it strikes the mid Atlantic and North Eastern coasts.
But bad is bad, and the aspect I watch most closely is the projected path of the center and the width of the storm path. I will probably evacuate my family and stay at a location which is expected to be on the edge of the threat. Forecasting keeps getting better and better, but realistically, it could do unexpected things in both direction and severity.
This article was certainly timely for me and many hundreds of thousands of others
Thanks! I appreciate that. Read also said, “If it’s a large area, the impacts will be a much worse than you think, just because of the duration. You can’t simplify this to an index. Surge is even worse. A scientist put it very bluntly. ‘We already have an index for surge. It’s called feet.’”
Reply | Report Abuse | Link to thisAs a humanities scholar I appreciate the fact that this article is so accessible in language, while allowing readers to be aware of the pertinent research. This is not always the case for those of us attempting to cross disciplines!
Reply | Report Abuse | Link to thisIn 1957 I was transferred to Guam which experienced the strongest typhoon of the time: sustained winds of 155/160 and gusts exceeding 200mph. In a low reinforced concrete building it was like experiencing an earthquake that lasted for several days. The wind noise sounded like a jet plane and the force moved large uncabled objects around. Millions of dollars damage(a very large sum at the time) was done to the rather primitive US Territorial island.
Reply | Report Abuse | Link to thisThe new category?
Reply | Report Abuse | Link to thisOne Red Spot.
Two Red Spot.
Three Red Spot.
This just never ends. And, visible from other planets. Good luck getting insurance.
Perhaps strenght 6 hurricanes won't come this season,the sun has just started to awake from an historical low, but for sure they'll arrive later,unless the cooling effect of winds coming from african deserts and covering the hurricane birth places with dust impeding sun heat from heating air and ocean is repeated again. This saved the americas from an extreme hurricane season some years ago.
Reply | Report Abuse | Link to thisWhat is still a mystery is with everything getting greater, ruthless, worse, why are we still using the "same old, same old." Sure it has worked well for us in the past but with change comes adaptability. We need to hold into account the new beasts coming our way and though the categories may sometimes be misguided warnings at least there of some sort, as to none at all. We need to get a better idea of what’s coming after us, and need better mechanisms to not just take in wind speed but better forecast the mess that’s in store.
Reply | Report Abuse | Link to thisWell, looks like the alarmists have got it wrong. Again. Of course if you forecast disaster every time sooner or later one of your predictions might get it right. That is what all prophets rely upon. Plus reinterpretation of what they actually prophesised.
Reply | Report Abuse | Link to thisUnfortunately, even amongst experts in many fields, comparable classification systems are a problem. Any changes need to run in parallel with the existing methods for a long time. Just how long is another question? Unfortunately this can also lead to tragic or just very expensive mistakes. The loss of a spacecraft to Mars some years ago was attributed to confusion between metric & imperial systems. Surely the old imperial system should have been consigned to the dust bin of history by now.
Reply | Report Abuse | Link to thisWith hurricanes & Earth quakes, the growing world population inevitably results in greater human impact & a perception that things are getting worse when there is no solid evidence to support this over historical time spans let alone geological periods.
The issue of grading natural events certainly needs clarifying. Full credit & support to those who are grappling with methods to address this problem.
Being a resident of Florida; where hurricanes are collectively an issue that we must deal with annually, I would have appreciated more precautionary advice than "run from the water, hide from the wind." Seeing as a new category implies possibly stronger storms, it is only natural for civilians in such exposed zones to despair and reach out for guidance. Having said that, the article was otherwise precise and adequately informative.
Reply | Report Abuse | Link to thisGalveston. ( Song by Johnny Cash )
Reply | Report Abuse | Link to thisGreat article. I loved it. I love intense storms, so if they make a Category 6, I'm for it. Of course, I don't wish for harm to come to any residents in it's path. I'm just saying, I'd like to experience a Category 6 hurricane. I think that would be awesome.
Reply | Report Abuse | Link to thisI did like this article and thought it would benefit from added information. NOAA provides the following short descriptions of the categories[1]:
Reply | Report Abuse | Link to this1: Very dangerous winds will produce some damage
2: Extremely dangerous winds will cause extensive damage
3: Devastating damage will occur
4: Catastrophic damage will occur
5: Catastrophic damage will occur
So, even based on those descriptions, it is pretty obvious that the categories do not provide much dynamic range and that hands are thrown up and you should just GTFO. There's a good reason for this. The scale is linear with wind speeds:
1: 74-95 mph
2: 96-110 mph
3: 111-130 mph
4: 131-155 mph
5: 155-infinity mph
This is rather ludicrous for this simple equation:
F = 1/2*p*v^2*Cd*A [2]
F is the force on the object the wind is blowing on, p is the mass density of the air, v is the velocity of the wind, A is the area of the object exposed to the wind and Cd is a drag coefficient.
Note, I'm simplifying because knowing the exact forces are not necessary, just the scale of the force. You don't have to have all of the numbers in place to see that as the velocity of the wind goes higher, the forces are proportionally higher as an exponential (v^2).
This means that a sustained wind of 95mph produces 1.65 times more force than a sustained wind of 74mph (i.e. the range of a Cat 1 storm).
This difference levels off because of the difference between the low-high numbers in the categories become relatively smaller compared to x. However, you can see in the short descriptions that once you've passed a sustained wind speed of 100mph, you're already in the GTFO range.
There is a relationship between a sustained wind and how much overall power (as in energy) is in a storm, which seems pretty useful to me.
[1]http://www.nhc.noaa.gov/sshws.shtml
[2]http://en.wikipedia.org/wiki/Drag_equation
I definately agree. If they are going to add a Category 6 then they should readjust all the other categories and break down 6 so that wat happened to category 5 (having an open cap) doesn't happen to the category 6.
Reply | Report Abuse | Link to thisBeing this is my first year of school in Miami, FL and I otherwise reside in New Jersey I've never experienced a hurricane. I have, however, watched news in which hurricanes have devastated various areas of the country. The last one I remember being a category 5 hurricane was Katrina and seeing how awful that was I can't even begin to imagine what a category 6 hurricane can do.
Reply | Report Abuse | Link to thisBeing this is my first year of school in Miami, FL and I otherwise reside in New Jersey I've never experienced a hurricane. I have, however, watched news in which hurricanes have devastated various areas of the country. The last one I remember being a category 5 hurricane was Katrina and seeing how awful that was I can't even begin to imagine what a category 6 hurricane can do.
Reply | Report Abuse | Link to thisI agree with Bill Read's idea that it's time to do away with the Saffir-Simpson scale and come up with something that more accurately describes the dangers of an incoming hurricane. Irene is the perfect example of a storm that did way more damage than you might otherwise expect from a weakening Cat 1 hurricane. It wasn't even a hurricane anymore by the time it hit NYC, but I don't think anyone who was flooded out of their homes in the northeast cares what category it was. The National Weather Service now has an "impact scale" for northeast snowstorms. Perhaps a similar scale is needed for hurricanes.
Reply | Report Abuse | Link to thisKatrina, when it hit Louisiana, was a mere Cat 3. If it had hit a Dutch city for example instead of a "chocolate" one it would have hardly been an issue. Let's not confuse science and culture.
Reply | Report Abuse | Link to thisThe Safir-Simpson scale fails to characterize a cyclone's storehouse of energy, its cargo of moisture, or its size. Energy, moisture and size should be, considered together, better indicators of the dangers a cyclone poses than wind speed alone.
Reply | Report Abuse | Link to thisI think I would like to see a new measurement scale for cyclones which considers these variables.