Are Category 4 and 5 hurricanes increasing in number?

By: Dr. Jeff Masters , 4:36 PM GMT on March 27, 2006

Share this Blog
0
+

In September 2005, a paper published in Science magazine reported that worldwide, the number of Category 4 and 5 hurricanes had increased 80% in the past 30 years. The paper, (Webster et al., 2005), titled "Changes in Tropical Cyclone Number, Duration, and Intensity in a Warming Environment", linked the rise in storms to increasing sea surface temperatures and concluded that "global data indicate a 30-year trend toward more frequent and intense hurricanes." The authors, led by Dr. Peter Webster of Georgia Tech and Dr. Greg Holland of the National Center for Atmospheric Research, argued that this was consistent with climate models that have predicted a future increase in frequency of the most intense hurricanes due to human-emitted greenhouse gases. This paper, along with another paper published in August, "Increasing Destructiveness of Tropical Cyclones over the past 30 years", by Dr. Kerry Emanuel of MIT, showing an increase in hurricane power and longevity in recent years, created a huge stir in the media. However, there is a large amount of uncertainty in the hurricane intensity data used by both papers, and their findings should be considered as preliminary evidence that the global incidence of Category 4 and 5 hurricanes may be increasing. There are good reasons to believe that the actual increase in Category 4 and 5 hurricanes is far lower than the 80% increase found by Webster et al.



Figure 1. Dr. Chris Landsea (right) and Dr. Greg Holland (left) presented their papers on the hurricane/global warming controversy at a January 31, 2006 session of the annual meeting of the American Meteorological Society. The standing-room only crowd was treated to a clash of opinions about whether hurricane intensity is being affected by global warming.

Other hurricane scientists disagree
The papers by Webster et al. and Emanuel have created considerable controversy in the hurricane science community. Many hurricane scientists disagree with the new results, and have disputed them in new papers submitted for publication. I will examine the arguments of three of these scientists here. Keep in mind that the Webster et al. paper went through peer review--it was revised based on the recommendations of at least two anonymous reviewers who read the paper before publication. The arguments of the other scientists disputing the paper have not been subject to peer review, and may have more errors or omissions than peer-reviewed work would have. The three scientists are:

Dr. Bill Gray of Colorado State University, who is famous for his successful long-range hurricane predictions and nearly 50 years of hurricane research and forecasting, submitted his critique to Science for publication, but the journal rejected it, since the document had already been published (on Dr. Gray's web site). Journals typically do not publish material that has been published elsewhere. In his abstract, Dr. Gray says: "I do not agree that global Category 4-5 tropical cyclone activity has been rising, except in the Atlantic over the last 11 years. The recent Atlantic upsurge has explanations other than global temperature rise".

Dr. Chris Landsea, Science and Operations Officer at the National Hurricane Center, chaired a standing-room only session exploring the hurricanes/global warming connection at the 2006 meeting of the American Meteorological Society (AMS). He presented a talk with additional evidence supporting Dr. Gray's position.

Dr. John Knaff, a hurricane researcher at the NOAA/Cooperative Institute for Research in the Atmosphere Colorado State University, has performed an extensive re-analysis of Northwest Pacific typhoons, and questions the intensity estimates used by Webster et al. for typhoons during the period 1966-1987. His paper, "Reexamination of Tropical Cyclone Wind-Pressure Relationships" has been accepted for publication to Weather and Forecasting, and will probably be published in late 2006.

Who are Webster et al.?
Lets examine the credentials of the Science paper's authors. The primary author, Dr. Peter Webster of Georgia Tech, holds a Ph.D. from MIT and has received the most prestigious award issued by the American Meteorology Society--the Carl Gustav Rossby Research award. Webster's primary expertise is not hurricanes--he has mostly studied monsoons. However, the second author, Dr. Greg Holland of the National Center for Atmospheric Research, is a hurricane expert. He earned his Ph.D. in 1983 at Colorado State as a student of Dr. Bill Gray, and has authored over 100 hurricane-related journals articles or book chapters. One of the other co-authors, Dr. Judith Curry, is the Chair of the Georgia Tech School of Earth and Atmospheric Sciences. So, the paper's authors have a track record of producing high-quality research that should be taken seriously.

The theoretical basis for connecting hurricane intensity and global warming
Hurricanes act as giant heat engines, so it is logical to assume that an increase in sea surface temperatures (SSTs) will make more intense hurricanes. Indeed, there is a general consensus among hurricane scientists that an increase in SSTs due to global warming, should, in theory, lead to more intense hurricanes. Theory predicts that hurricane wind speeds should increase about 5% for every 1 degree Centigrade increase in tropical ocean temperature (Emanuel, 1987). Computer models confirm this tendency, but assign a slightly smaller magnitude to the increase (Knutson and Tuleya, 2004). Given the expected 1.5� to 4.5� C warming of Earth's climate expected by 2100, theory predicts a gradually increasing frequency of Category 4 and 5 storms.

Global warming in the past century has increased ocean temperatures about 1�F (0.5�C) which should correspond at most to about a 2.5% increase in hurricane wind speeds. If this theory is correct, an upper-end Category 3 hurricane with wind speeds of 130 mph--like Hurricane Katrina at landfall--owes 2-3 mph of its sustained winds to global warming. Hurricane wind speeds are estimated to the nearest 5 knots (5.8 mph), and one can get a general idea of what percent increase we've seen in Category 4 and 5 hurricanes due to global warming by looking at the number of high end Category 3 hurricanes (winds of 130 mph) and low end Category 4 hurricanes (135 mph winds). If we assume a 2-3 mph increase in winds of these storms is due to global warming over the past 35 years, one would expect to see a 5% increase at most in Category 4 and 5 hurricanes. An increase this small is not detectable given the current accuracy of estimating hurricane winds, and the relatively few number of of these storms that occur each year. This expected maximum 5% increase is quite a disagreement with the 80% increase found by Webster et al.! So, either the measurements are wrong, or the theory is wrong--or a combination of the two. I believe it may well be a combination of the two. The fact that the originator of the intensity theory (Kerry Emanuel) is one of the scientists who is advocating that the theory may be in error, is reason enough to doubt the theory. The formation and intensification of hurricanes are not well understood, and it would be no surprise if major revisions to intensity theory are made in the future. However, such a wide difference between the theory and the reported trends should make us suspicious of the observed data, as well.

Sea Surface Temperatures have increased since 1970
Webster et al. show a plot (Figure 2) of the sea surface temperature (SST) in the six major ocean basins that support tropical cyclones. Since 1970, SSTs in all the oceans have risen by up to .5� C. The paper chooses to look only at the period from 1970 to the present, since 1970 is the approximate time when global satellite measurements of tropical cyclone intensity became available. Before 1970, there are reliable intensity measurements only in the Atlantic and Northwest Pacific, thanks to the Hurricane Hunters. These measurements began in 1944 in the Atlantic and 1945 in the Northwest Pacific (but stopped in 1987 in the Pacific).



Figure 2. Running 5-year mean of SST during the respective hurricane seasons for the principal ocean basins in which hurricanes occur: the North Atlantic Ocean (NATL: 90� to 20�E, 5� to 25�N, June-October), the Western Pacific Ocean (WPAC: 120� to 180�E, 5� to 20�N, May-December), the East Pacific Ocean (EPAC: 90� to 120�W, 5� to 20�N, June-October), the Southwest Pacific Ocean (SPAC: 155� to 180�E, 5� to 20�S, December-April), the North Indian Ocean (NIO: 55� to 90�E, 5� to 20�N, April-May and September-November), and the South Indian Ocean (SIO: 50� to 115�E, 5� to 20�S, November-April). Reprinted with permission from SCIENCE 309:1844-1846 � 2005 AAAS. Permission from AAAS is required for all other uses.

The global number of hurricanes has not increased

Webster et al. also present plots of the global frequency of tropical storms, hurricanes, and the number of days those storms are present (Figure 3). No trend is apparent in these plots, and the paper states that "against a backdrop of increasing SST, no global trend has yet emerged in the number of tropical storms and hurricanes." So far, all hurricane scientists are in agreement.



Figure 3. Global time series for 1970-2004 of (A) number of storms and (B) number of storm days for tropical cyclones (hurricanes plus tropical storms; black curves), hurricanes (red curves), and tropical storms (blue curves). Contours indicate the year-by-year variability, and the bold curves show the 5-year running average. Reprinted with permission from SCIENCE 309:1844-1846 � 2005 AAAS. Permission from AAAS is required for all other uses.

An 80% increase in Category 4 and 5 hurricanes?

Webster et al. present a plot (Figure 4) where of the number of Category 1, Category 2 and 3, and Category 4 and 5 storms, averaged into 5-year "pentads". The results show little change in the statistics of Category 1, 2, and 3 hurricanes, but a startling increase in Category 4 and 5 hurricanes. These most intense and dangerous storms on Earth have increased from 50 per five-year period in the 1970s, to 90 in the past decade--a near doubling!



Figure 4. Intensity of hurricanes according to the Saffir-Simpson scale (categories 1 to 5). (A) The total number of category 1 storms (blue curve), the sum of categories 2 and 3 (green), and the sum of categories 4 and 5 (red) in 5-year periods. The bold curve is the maximum hurricane wind speed observed globally (measured in meters per second). The horizontal dashed lines show the 1970-2004 average numbers in each category. (B) Same as (A), except for the percent of the total number of hurricanes in each category class. Dashed lines show average percentages in each category over the 1970-2004 period. Reprinted with permission from SCIENCE 309:1844-1846 � 2005 AAAS. Permission from AAAS is required for all other uses.

An 80% increase in Category 4 and 5 hurricanes? Not!

Here's where the critics of Webster et al. differ. Let's look at the criticisms one ocean basin at a time. First: the Southern Hemisphere oceans, and the part of the Indian Ocean in the Northern Hemisphere. These regions are responsible for 25% of the world's Category 4 and 5 hurricanes. Dr. Gray criticizes the quality of the data in the Indian Ocean and Southern Hemisphere ocean basins during the period 1975-1989, remarking: "In the late 1970s I visited all the global tropical cyclone centers and observed their satellite capabilities and the training of their forecasters as part of a World Meteorological Organization (WMO) tropical cyclone trip that I was commissioned to make. The satellite tools and forecaster training in the tropical cyclone regions of the Indian Ocean and Southern Hemisphere during the 1975-1989 period was not adequate for the task of objectively distinguishing Category 4-5 hurricanes from Category 3 hurricanes or to always be able to confidently distinguish Category 4-5 hurricanes from Category 1-2 hurricanes." Dr. Gray does not provide any details about how how this lack of training could have led to a systematic error in classifying too few storms at Category 4 and 5 intensity. However, Dr. Landsea did cite an example of this in his talk at the 2006 American Meteorological Society meeting--for a number of years after 1974's Tropical Cyclone Tracy devastated Darwin, the Australians never assigned an intensity higher than Tracy to any storm because they believed Tracy was the strongest a storm could be in the Australian region. Tracy was a weak Category 4 cyclone with 135 mph winds and a 954 mb pressure. This was a false assumption, as many cyclones stronger than Tracy have formed in Australian waters.

This brings up the most serious weakness in the Webster et al. paper--they do very little discussion of the uncertainty in hurricane intensity measurements. Hurricane intensity is characterized by a 1-minute measurement of maximum sustained winds at ten meters above the surface. In practice, this quantity is virtually never measured, but must be inferred indirectly from other measurements. All of these inferred measurements of wind speeds have errors. Satellite estimates of hurricane intensity are often wrong by a full category on the Saffir-Simpson scale--or even two categories. This is particularly true when there are only two geostationary satellites covering the Earth, as was the case for much of the 1970s, and part of the 1980s. I learned this the hard way during my stint with the Hurricane Hunters when I flew into Hurricane Hugo in 1989 expecting a Category 3 hurricane based on satellite estimates. The problem was that one of the GOES satellites had failed earlier that year, leaving just one satellite to cover all of the U.S. and Atlantic Ocean. This one satellite was positioned much farther west in order to see all the way to California, and thus had a poor, oblique view of hurricanes out over the Atlantic. If a satellite can't see all the way to the bottom of the eye of a hurricane because of an oblique viewing angle, it will come up with an eye temperature that is too cool, and thus an intensity estimate that is too low. Hugo turned out to be a Category 5, and made us pay dearly for our mistake. Similarly, a systematic underestimation of hurricane intensities in the 1970s is quite possible, due to the oblique viewing angle that the relatively few geostationary satellites afforded during that period.

Furthermore, Dr. Landsea argued, the technique used to perform satellite estimation in all ocean basins of hurricane intensity (the Dvorak technique) did not even get invented until 1972--two years after the start of the data used by Webster et al. It wasn't until 1984 that the Dvorak technique was extended to infrared satellite imagery. So, between 1972 and 1984, all satellite hurricane intensity estimates were done on visible satellite imagery, and were unavailable at night. In addition, measurement errors from the first generation of infrared satellite instruments was much higher, since their resolution was a relatively poor 9 km--compared to the 4 km resolution of today's instruments. Dr. Landsea called for a major re-analysis effort of the old satellite photos from the 1970s and 1980s to try to quantify some of these errors. He argued that his preliminary look at old satellite images from the Northern Indian Ocean from 1970 to 1989 had already revealed five additional storms that may have been Category 4 or 5. Webster et al. found only one Category 4 or 5 hurricane for this time period there. Dr. Landsea suggested that until a full re-analysis took place in all ocean basins, the quality of the historical global hurricane intensity data was not high enough to be able to see a possible increase in the number of Category 4 and 5 hurricanes.



Figure 5. Number of Category 4 and 5 hurricanes in the Indian Ocean and Southwest Pacific Ocean (off the east coast of Australia) since 1970. A a rather dramatic rise in recent years is apparent. Data from 1970-2002 are taken from a reanalysis of available data from Australia, Fiji, and the Joint Typhoon Warning Center, done by Charlie Neumann. All the data used in the Webster et al. study are available from Dr. Judith Curry's web page.

Dr. Holland spoke after Dr. Landsea, and agreed that a major re-analysis effort was needed in order to help quantify some of the errors in hurricane intensities. He rebutted Dr. Landsea's arguments by pointing out that given the very large rise in Category 4 and 5 hurricanes in the Southern Hemisphere and Indian Oceans, about 50% of all Category 1 and 2 hurricanes would have to be re-analyzed as Category 4 and 5 storms to invalidate their results in that region. While acknowledging the the data was bad in the 1970s, he maintained that nobody thought it was that bad.

Summary of the Southern Hemisphere and Indian Ocean data

If we restrict ourselves to just looking at the Southern Hemisphere and Indian Ocean data since 1989--the date when everyone agrees that the data quality is reasonable--there is not enough data to be sure of any kind of trend (Figure 5). So until better intensity estimates of hurricanes in the Indian Ocean and Southern Hemisphere ocean basins from 1970-1989 are available, one should view the results of Webster et al. with caution for these regions. Still, there is such a large increase in Category 4 and 5 hurricanes that it is unlikely that re-analysis will find that all of this increase in unreal.

--To be continued Tuesday afternoon--

Jeff Masters

References
Emanuel, K.A., "The dependence of hurricane intensity on climate", Nature, 326, 483-485, 1987.

Emanuel, K.A., "Increasing Destructiveness of Tropical Cyclones over the past 30 years, Nature, 436, 686-688, 4 August 2005.

Knaff, J.A., and R.M. Zehr, "Reexamination of Tropical Cyclone Wind-Pressure Relationships", accepted to Weather and Forecasting, 2006.

Knutson, T.R., and R.E. Tuleya, "Impact of CO2-Induced Warming on Hurricane Intensity and Precipitation: Sensitivity to the Choice of Climate Model and Convective Parameterization," Journal of Climate 17, 18: 3477-3495, 2004. http://www.gfdl.noaa.gov/reference/bibliography/20 04/tk0401.pdf

Webster, P.J., G.J. Holland, J.A. Curry, and H.-R. Chang, "Changes in Tropical Cyclone Number, Duration, and Intensity in a Warming Environment", Science, 309, 1844,1846, 16 September 2005.

Reader Comments

Comments will take a few seconds to appear.

Post Your Comments

Please sign in to post comments.

or Join

Not only will you be able to leave comments on this blog, but you'll also have the ability to upload and share your photos in our Wunder Photos section.

Display: 0, 50, 100, 200 Sort: Newest First - Order Posted

Viewing: 43 - 1

Page: 1 | 2 — Blog Index

43. Skyepony (Mod)
1:07 AM GMT on March 28, 2006
Dr Masters or anyone... Some have brought up how these papers & storms like Elipsion are showing that shear & other factors play a much smaller role, compared to SST, than previously thought. My problem with these theorys is the North Indian Ocean, with it's average SST, well the highest, around 29.5C. Yet the total # of canes for the NIO is by far the lowest.

Credit Webster bit on NOVA ScienceNow

It can't be all SST, what's the limiting factor? Little ocean?, shear?
Member Since: August 10, 2005 Posts: 161 Comments: 37433
40. Skyepony (Mod)
12:15 AM GMT on March 28, 2006
Another point on Dr Grays paper~ He starts comparing Cat 1&2 to 3,4&5. Totally diluting the #s forming part of his rebuttal. It would be all good except the papers he's trying to disprove are about #s of Cat 1,2,3 to 4&5's. Left me disappointed.
Member Since: August 10, 2005 Posts: 161 Comments: 37433
39. Skyepony (Mod)
11:38 PM GMT on March 27, 2006
Excellent blog~ We've been looking at some of this as it has been coming available, to see it all together, with added info we haven't checked into, alotta great info. Still reading through the links.

Had to check out Dr Gray's rebuttals. The abstract against Emanuel's paper was a little upsetting as he contended that Emanuel was tying this to human caused global warming. Sounded slanted from the get go, if you'd read Emanuel's paper.
(from Dr Gray's paper)
The author
associates these frictional energy dissipation increases with rising mean sea
surface temperatures (SSTs) and implies that these SST increases may, in part,
be related to human activity.


I saw a NOVA ScienceNow where Emanuel & Webster was asked at the end, if this was due to human caused global warming, both said that's not what this paper is about, there is no such kind of mention of anything suggesting that in the research & they didn't know. Reading their papers I saw no hint this was caused by humans. Also an interview with Judith Curry she says:

People have accused us of linking global warming with Katrina. We didnt even use the expression global warming in the paper. We talked about an increase in global tropical sea surface temperature.

I totally agree the numbers should be rechecked, it should be approached from all angles to see how the theory holds, but with an open mind, not misquoted intent.
Member Since: August 10, 2005 Posts: 161 Comments: 37433
38. rwdobson
10:49 PM GMT on March 27, 2006
sayhuh, i live in KC too. near downtown overland park...we barely even got 0.01" of rain out of the Mar 12 outbreak...near us, the bigger event was the fire at the gallery in downtown OP. we got a lot of nasty smoke hanging in the air during that.
Member Since: June 12, 2002 Posts: 0 Comments: 1588
36. sayhuh
10:16 PM GMT on March 27, 2006
MichaelSTL,
To followup on your blurg from SPC, its looking like a possible repeat of earlier this month..sigh. Living in KC, I don't like the NAM 18Z 78-84 500 vort. Also, the 300mb with RH and other factors are making me get ready to chase...we shall see. Link
Member Since: Posts: Comments:
35. PhantomPower
10:16 PM GMT on March 27, 2006
I have a possibly dumb question: What if the effects of SST are being looked at the wrong way? Maybe it's more clarifying to say that lower SST acts as a brake on storm development, and that as temps rise, that brake goes away. It would be related to the "deep vortex" theory that has been proposed to explain the rapid intensifications we say this year. Increasing frequency of storms, and cat-4-plus storms, are happening not because of the increase in heat energy at the ocean surface, but because the ocean surface is passing some critical point, where it fails to act as a brake on storm development. The resulting storm is out of proportion to the relatively small heat increase from the ocean surface.
Member Since: Posts: Comments:
34. rwdobson
9:39 PM GMT on March 27, 2006
"The principles are the same so yes you can."

no, not really. you may or may not be able to do the same thing. even if the theory holds, the fact is that water and air are fluids with very different fluid properties. so it is very likely that IN PRACTICE the results will be different. to use a simple analogy, you usually don't use the same pump to pump air as you use to pump water.

the burden of proof is on you, the "inventor" to show that the tunnels would work in practice. just because something works on hot air exhausting from a power plant does not mean it will work on cool water in the ocean.
Member Since: June 12, 2002 Posts: 0 Comments: 1588
31. HurricaneMyles
9:22 PM GMT on March 27, 2006
Yup, thats the picture. I'm having way too much trouble with html today, so thanks for taking care of it for me. :D
Member Since: January 12, 2006 Posts: 5 Comments: 827
30. rwdobson
9:18 PM GMT on March 27, 2006
"Ever hear of a STEAM JET AIR EJECTOR (SJAE). It creates an area of lower pressure so that air can be removed from condensers at power plant"

But we are not talking about power plants. We're talking about the ocean. Just because you can make something work in a condenser at a power plant doesn't mean you can do the same thing in the ocean.
Member Since: June 12, 2002 Posts: 0 Comments: 1588
27. HurricaneMyles
9:14 PM GMT on March 27, 2006
I would say the chances are good. She already has a well defined eye.

Navy
Member Since: January 12, 2006 Posts: 5 Comments: 827
22. rwdobson
8:58 PM GMT on March 27, 2006
and by the way, saying "bernoulli principle, airplanes can fly" doesn't cut it as proof.
Member Since: June 12, 2002 Posts: 0 Comments: 1588
21. rwdobson
8:53 PM GMT on March 27, 2006
No one has ever doubted that changing SSTs can affect hurricane intensity.

What everyone doubts is whether your tunnels would actually change SSTs, and whether the change would be enough to affect hurricanes, and what the affects on ocean life and the overall climate would be.

Your statement "my tunnels would have a devastating effect on hurricanes but not the environment" is absurd. You have absolutely no proof of either part of that statement, other than some conjecture. It is quite possible, in fact, that the tunnels would have more effect on the environment than on hurricanes.
Member Since: June 12, 2002 Posts: 0 Comments: 1588
19. snowboy
2:37 PM EST on March 27, 2006
Just a quick thank you Dr. Masters for such an excellent article, giving us lots of information, and the pros and cons of both sides' arguments..
Member Since: Posts: Comments:
18. HurricaneMyles
7:39 PM GMT on March 27, 2006
I'd ask what are you talking about, because I've seen nothing to support your tunnels, but I dont even want to know.

As far as why does it have to persist for 5 months to be an official la nina is because things can change rather dramatically in the short term. Why they picked 5 months, I dont know, must be where short term variation lowers to a certain point.
Member Since: January 12, 2006 Posts: 5 Comments: 827
15. louastu
2:10 PM EST on March 27, 2006
Is there a reason why La Nina conditions have to persist for 5 months before they list it as an official La Nina? It seems to me that if La Nina conditions are around for a week that they could begin to result in unusual weather patterns across the globe.
Member Since: Posts: Comments:
14. hurricanechaser
6:53 PM GMT on March 27, 2006
Hey everyone,

Here is the link from the CPC that shows that a weak La Nina began to develop in September of 2005 and continued to increase in intensity by November that mostly likely encouraged our record breaking 2005 hurricane season (i.e so many unusual late season storms).

It is important to note that it isn't considered an "offcial" La Nina phase of the ENSO cycle until there have been 5 consecutive months of below normal waters temps in the equatorial Central Pacific that in this case began in September and became an "official" weak La Nina in Febuary 2006.

Even though the 2005 season registers as an "official" neutral phase of ENSO cycle for the aforementioned reason, the La Nina conditions had begun to affect the 2005 season beginning in September and most likely played a very significant role in helping so many storms materialize thereafter.:)

Once again, I hope everyone has a great week and may God bless each one of you.:)

Your friend,
Tony

Link
Member Since: Posts: Comments:
13. HurricaneMyles
6:57 PM GMT on March 27, 2006
Finmet, Did you just say that a global temp rise of 2-4C will make it uninhabitable, less the spelling error?

If so, that's just completely wrong. Life is far too tenacious to die out because of a couple of degree change in temperature. Hell, it survived ice ages and metoer strikes, I think it will survive a little warming. In fact, in the long run, life does better in a warmer environment.
Member Since: January 12, 2006 Posts: 5 Comments: 827
12. HurricaneMyles
6:53 PM GMT on March 27, 2006
Actually, a low pressure system can gain tropical characteristics at any temperature water. Look at the low pressure system off Canada's coast, it's warm core with lots of clouds around the center and its over waters around 10C. Save for the fronts, looks pretty tropical, huh?

Also, polar lows develope hurricane like eyes and these are over the artic regions.
Member Since: January 12, 2006 Posts: 5 Comments: 827
11. mtwhitney
6:48 PM GMT on March 27, 2006
a low pressure system can gain tropical charactoristics over water that is in the 70 degree range, but this is rare in the summer when water temps are in the 80's.
Member Since: Posts: Comments:
10. Finnmet
6:30 PM GMT on March 27, 2006
For me its clear that at this moment we have to learn more about hurricanes.Global warming in the past century has increased ocean temperatures about 1F (0.5C) which should correspond at most to about a 2.5% increase in hurricane wind speeds. If this theory is correct, an upper-end Category 3 hurricane with wind speeds of 130 mph--like Hurricane Katrina at landfall--owes 2-3 mph of its sustained winds to global warming. Hurricane wind speeds are estimated to the nearest 5 knots (5.8 mph), and one can get a general idea of what percent increase we've seen in Category 4 and 5 hurricanes due to global warming by looking at the number of high end Category 3 hurricanes (winds of 130 mph) and low end Category 4 hurricanes (135 mph winds). If we assume a 2-3 mph increase in winds of these storms is due to global warming over the past 35 years, one would expect to see a 5% increase at most in Category 4 and 5 hurricanes.
I thing this is a wrong theory.If the global temperatures increas with 2-4 deegrees C,the our climate will make the planet anhabittable.A study in Europe shown that if the annual temperature rise from 8 to 9C,monthly temperatures will rise with 2 degrees and daily temperatures will rise with 3-4 degrees C and there will be dramatic changes in climate of any country.
I don't thing that a rise with 1 C in SSt have just a 5% in increasing number of cat.4 or 5.I thing that % is much higher,around 20-25%.When Wilma was forming in middle of october,the SSt was around 29-30C.Imagine if a hurricane like Wilma will forming this year in middle of september in the same region with SSt of 31C!
9. hurricanechaser
6:36 PM GMT on March 27, 2006
Hey everyone,

I am very busy right now with my wife recovering from a bad accident (doing so much better though) and our new baby expected literally any day now.:)

That being said, I don't have the time to write a blog giving my own personal reasons as to why I agree with Dr. Gray and Chris Landsea on this issue and not with the central premise that category 4 & 5 hurricanes have been increasing Worldwide during the past 30 years and the possible insuation that greenhouse gas emissions are somehow responsible for this perception.

On a different note, I thought I would add that the late season storms that led to our record breaking season were most likely the result of a weak La Nina that began to develop during the Month of September of 2005.

I wish I had time to write a couple of blogs on these two fascinating subjects, but unfortunately I won't for another two months or so at the earliest.

In the meantime, I hope each of you have a wonderful day and may God truly bless each and every one of you.:)

Your friend,
Tony


Member Since: Posts: Comments:
7. mtwhitney
6:25 PM GMT on March 27, 2006
"Theory predicts that hurricane wind speeds should increase about 5% for every 1 degree Centigrade increase in tropical ocean temperature (Emanuel, 1987)."

When a large area of water is 80 degrees f, it is capable of producing a catagory 1 hurricane. When the water temperature is around 83 - 84 degrees, a catagory 4 hurricane is possible, at 88 degrees the most powerful cat 5 hurricanes occur. This means that the difference between a cat 1 and a cat 5 is about 4 degrees celcius, this is a much greater increase than a 5% increase in wind speed for every 1 degree celcius increase in water temperature, can someone explain why there is an apperent difference in this?

Also, is it possible that in some hurricane basins the number of cat 4 and 5 storms is increasing while overall hurricanes are not increasing is because there can only be so many hurricanes in one spot, like in the pacific where each basin has 20 - 30 storms a year, the increase in water temperature or heat content can only increase the power of storms, not the number of storms.

also, if a hurricane needs water over 80 degrees to form, by increasing water temps a degree f, you are not only increasing the temperature of water from 80 to 81, or 81 to 82 degrees, but the area of 80 degree water is also expanding, thereby increasing the range where hurricanes can form and grow. There is also the factor of heat content, the depth of 80 degree water, with the arctic warming, there should be less cold water feeding into the deeper waters, increasing the total heat content of the waters. The warming of the arctic should have a much greater impact on the atlantic basin, as there is a much greater heat exchange between the atlantic and arctic oceans that there is with the pacific and indian oceans.
Member Since: Posts: Comments:
5. ForecasterColby
6:21 PM GMT on March 27, 2006
I still love that name...Landsea. What an appropriate name for a climate researcher.
4. fredwx
1:00 PM EST on March 27, 2006
Correction: The lack of data regarding tropical cyclones was for the Indian Ocean.
Member Since: Posts: Comments:
3. fredwx
12:25 PM EST on March 27, 2006
Great post.
I remember the 1970's as I was part of a ship weather routing company and there was indeed a lack of data regarding tropical cyclones. The area had little satellite coverage, no hurricane hunter planes and often the
cyclones were off the normal ship routes so there was very little surface reports to verify intensity.

Living in Florida, I am now concerned about an increase in major hurricanes (Cat 3-5) and took a look at this a few weeks ago. What I found is that Florida seems to targeted by major hurricanes during the warm phase of the Atlantic Multidecadal Oscillation (AMO).

The AMO is a long cycle of changes in the sea
surface temperature of the North Atlantic
Ocean. During the last warm cycle which lasted about 40 years (1925-1965) there were 18 major hurricanes that hit Florida.
That's about 1 every other year (0.45/yr)while during the 30 year cool phase from about 1965-1995 there were only 3 or about 1 every
10 years (.10/yr).

Link to my post
Member Since: Posts: Comments:
2. michalp
5:22 PM GMT on March 27, 2006
so it seams to me that there may be a sort of self fueling effect to higher ssts. If a hurricane has slightly higher speed, then it is slightly better able to control/overcome higher wind sheer, so it is able to go faster, and so on.

Also wouldn't global warming also lead to warmer air. If the air is warmer wouldn't the instability that causes hurricanes be weaker?
Member Since: Posts: Comments:
1. RL3AO
4:46 PM GMT on March 27, 2006
first!

nice post Dr. Masters
Member Since: Posts: Comments:

Viewing: 43 - 1

Page: 1 | 2 — Blog Index

Top of Page

About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.