Are Category 4 and 5 hurricane increasing globally? (Part II)

By: Dr. Jeff Masters , 2:04 PM GMT on March 31, 2006

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In my blog for Monday, I opened the discussion of whether Category 4 and 5 hurricanes were increasing in number globally. Here's Part II of that discussion:

Northwest Pacific typhoon intensities questioned
The question of the integrity of the typhoon intensity data in the Northwest Pacific is critical, since this ocean basin accounts for fully 46% of the global Category 4 and 5 hurricanes since 1970. Dr. Gray and Dr. Knaff both question typhoon intensities measured by reconnaissance aircraft in the Northwest Pacific during the 1973-1986 period. The technique used to determine typhoon intensities during this period (the "Atkinson-Holliday" or AH technique), is thought to have significantly underestimated the maximum winds. Looking at a plot of all Category 4 and 5 activity since 1945 in the Northwest Pacific (Figure 6), one can that intense typhoons were about as common in the 1950s and 1960s as they were during 1990-2004, but took a major dip in the 1970s and 1980s during the period the AH technique was used. I asked Dr. Webster and Dr. Holland about the intense typhoon activity back in the 1950s and 1960s, and they argued that this activity was the result of high SSTs in the Northwest Pacific during that period. On his website, Kerry Emanuel argues that typhoon intensities were overestimated in the 1950s and 1960s. However, Knaff and Zehr (2006) make some convincing arguments that typhoon intensities during the 1973-1986 period were too low due to measurement error, and the number of Category 4 and 5 storms in the region have been roughly constant for the past 50 years. This paper has been accepted for publication in Weather and Forecasting, and will likely be published late this year. Dr. Knaff and Charles Sampson of the Naval Research Laboratory have performed a preliminary re-analysis of maximum typhoon intensities for the period 1966-1987 based on the Knaff and Zehr (2006) results, and this re-analysis will be presented at the upcoming 27th Conference on Hurricanes and Tropical Meteorology (April 24-28, 2006). They show that after correcting for the AH technique errors, the number of Category 4 and 5 typhoons during the 1966-1987 period increased by 1.5 per year, leaving only a slight upward trend in Category 4 and 5 typhoons during the period 1970 - 2004. The 16% increase in Category 4 and 5 typhoons found by Webster et al. during the past 15-year period is reduced to just 3%. Based on this new research, the results of Webster et al. may have to be modified. In particular, their global increase in storms from 1990-2004 compared to 1975-1989, as presented in that paper will be reduced from 57% to 42% if Dr. Knaff's typhoon re-analysis is accepted.


Figure 6. Number of Category 4 and 5 hurricanes in the Northwest Pacific Ocean since reliable records began in 1945. Data taken from the Joint Typhoon Warning Center "best track" database. Typhoon intensities from the period 1973 - 1986 were estimated using the "Atkinson-Holliday" (AH) technique, which may have underestimated typhoon intensity.

Northeast Pacific
Dr. Gray formulates the reasonable hypothesis that if one compares global major hurricane activity for the most recent ten years (1995-2004) with the previous ten years (1985-1994), one should see a significant difference, since global surface temperatures increased about 0.4� C between the two periods. He shows that the number of Category 3-4-5 hurricanes stayed exactly the same between these two periods--218 for each time period--if one excludes the Atlantic. I tabulated the results for just Category 4 and 5 hurricanes, and the results were very similar--135 storms storms globally (excluding the Atlantic) from 1985-1994, and 142 for 1995-2004. As most of you are aware, the Atlantic has seen a big increase in the number of intense hurricane the past ten years. Dr. Gray attributes to the Atlantic Multidecadal Oscillation (AMO), a natural cycle I discussed in an earlier blog. Dr. Gray offers another comparison, but just for Category 4 and 5 storms. The most reliable comparison one can make is using data from the Northeast and Northwest Pacific from the past 20 years. This excludes the issues of dealing with the natural AMO cycles in the Atlantic, and the poor data quality in the other ocean basins. Again, the data show essentially no difference between time periods. Indeed, when looking at the plot of Category 4 and 5 hurricane for the Northeast Pacific--the ocean area off the west coast of Mexico (Figure 7), and responsible for 19% of the world's Category 4 and 5 hurricanes--one sees no increasing trend in recent years.


Figure 7. Number of Category 4 and 5 hurricanes in the Northeast Pacific Ocean since reliable satellite intensity estimates began in 1970. Data taken from the National Hurricane Center "best track" database.

Atlantic
The Atlantic contributes only 9% of the world's Category 4 and 5 hurricanes, so is not much of factor when considering global numbers of these storms. Dr. Gray shows that the number of Category 4 and 5 hurricanes in the Atlantic has remained constant when one compares numbers from the past 15 years with an earlier active period from 1950-1964. However, this is a poor comparison. The period 1950-1964 fell entirely within a time when the warm phase of the AMO dominated the Atlantic, and had significantly enhanced intense hurricane activity (see Figure 8). The period 1990-2004 includes five years from the cold phase of the AMO, when intense hurricane activity was significantly down. Thus, comparison of 1950-1964 with 1990-2004 in the Atlantic is poor. One should make the comparison between data from the 11 years from the most recent warm phase of the AMO (1995-2005), and the previous warm AMO period we have good data for (1944-1969). This comparison shows that Category 4 and 5 hurricanes in the Atlantic have increased by 60% in the past 11 years compared to the previous active period 1944-1969. One can make a similar comparison for the cold phase of the AMO, contrasting the years 1970-1982 with 1983-1994. This comparison show no increase in Category 4 and 5 hurricanes for the later period with warmer SSts. I asked Dr. Landsea about the 60% increase in Category 4 and 5 hurricanes during the most recent warm phase of the AMO, and he thought that at least part of the increase could be explained by inadequate information from the Hurricane Hunters during that period. He explained that during that time, it was common in intense hurricanes for the Hurricane Hunters to get close enough to the eye to fix the storm on radar, but not actually penetrate through the eyewall into the eye. Who can blame them! The older aircraft like the DC-6 used during that time period were not safe to fly into Category 4 and 5 hurricanes. Dr. Landsea is working on a re-analysis project for the entire Atlantic hurricane database, but has only made it to the 1930s, and hopes to have a more definitive answer on the intensities of hurricanes during the 1950-1969 period in a few years.



Figure 8. Number of Category 4 and 5 hurricanes in the Atlantic Ocean since reliable aircraft reconnaissance intensity estimates began in 1944. Data taken from the National Hurricane Center "best track" database and not corrected for any suspected biases. The warm AMO periods are associated with enhanced intense hurricane activity, and are thought to be part of a natural decades-long cycle that affects only the Atlantic Ocean (as far as hurricane activity is concerned).

Conclusion
So who's right? Given the uncertainties in estimating tropical cyclone intensity presented by Drs. Gray, Landsea, and Knaff, plus the very large disagreement with the theory of hurricane intensification, it is unlikely that the large 80% increase in Category 4 and 5 hurricanes found by Webster et al. is real. There does appear to be some increase, but it is likely much smaller. Many troubling questions need to be answered, such as why comparison of the most recent ten years (1995-2004) with the previous ten years (1985-1994) shows almost no increase in Category 4 and 5 storms globally, during a period when a substantial increase in SST occurred.

All the scientists involved in this debate have stated the need for a rigorous re-analysis of all historical tropical cyclone data. However, there is currently little funding for such work. Dr. Knaff told me that his typhoon re-analysis work was unfunded, and that he did it because he felt strongly that the results of Emanuel (2005) and Webster et al. were inaccurate and needed to be challenged. Dr. Landsea's reanalysis of Atlantic storms is funded, but something he can only devote time to when his duties at NHC allow him. Dr. Knaff wrote me, "While I realize there are plans to reanalyze the Atlantic, the West Pacific, Southwest Pacific, and Indian Ocean are all being done piece by piece as part of several unfunded projects with little general support. If people are going to use the data for global studies, then NOAA, NSF or some other entity should fund a global reanalysis." I agree completely! Before I am willing to conclude that Category 4 and 5 hurricanes are indeed showing a significant increase, I want to see the science done with a better dataset, and covering a longer period of time. The NOAA Office of Global Programs or National Science Foundation needs to step in and fund this research.

While Category 4 and 5 hurricanes may indeed be increasing in frequency globally, one cannot yet say that global warming is the cause. Webster et al. close with the sentence, "attribution of the 30-year trends to global warming would require a longer global data record and, especially, a deeper understanding of the role of hurricanes in the general circulation of the atmosphere and ocean, even in the present climate state." Furthermore, global warming cannot be cited as the cause of recent intense storms, such a Hurricane Katrina, Hurricane Wilma, or Australia's Cyclone Larry and Cyclone Glenda.

Webster, Holland, and Curry have submitted another paper for publication titled, "Testing the Hypothesis that Greenhouse Warming is Causing a Global Increase in Hurricane Intensity". I'll be sure to review the paper when it comes out. In addition, earlier this month, the authors published another paper linking increasing SSTs to higher numbers of Category 4 and 5 hurricanes. The paper was called, "Deconvolution of the Factors Contributing to the Increase in Global Hurricane Intensity", and I plan to say more about this paper in my next blog on the global warming-hurricane intensification debate. Later on this Spring, I'll also talk about the 2005 paper by Dr. Kerry Emmanuel of MIT in Nature that found increases in global hurricane duration and power dissipated due to increasing SSTs.

Be sure to tune in Tuesday, when the Colorado State University forecasting team founded by Dr. Bill Gray releases their updated 2006 hurricane season forecast.

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.

Hoyos, C.D., P.A. Agudelo, P.J. Webster, and J.A. Curry, "Deconvolution of the Factors Contributing to the Increase in Global Hurricane Intensity", www.scienceexpress.org, 16 March 2006, 10.1126/science.1123560.

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

Virmani, J.I., and R. H. Weisberg, "The 2005 hurricane season: An echo of the past or a harbinger of the future?", Geophysical Research Letters 33, L05707, 2006 doi:10.1029/2005GL025517.

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.





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112. HurricaneMyles
4:16 AM GMT on April 02, 2006
I'm sure they said 'they work'. More likely they said they could possibly work. Anyways, please, just stop posting about it here. We've heard all you've had to say and you've failed to pursuade most, if not all, of us, so go somewhere else and try to win them over.
Member Since: January 12, 2006 Posts: 5 Comments: 827
109. HurricaneMyles
4:07 AM GMT on April 02, 2006
You're very good at switching to topic. Whatever their main goal may be these days, it's obvious that they doubt that your tunnels work just as much as most people here do. So please, stop spamming us with unsubstantiated claims.
Member Since: January 12, 2006 Posts: 5 Comments: 827
107. HurricaneMyles
4:01 AM GMT on April 02, 2006
I guess, like the rest of us, they dont believe your tunnels will do all the amazing things you say they do. I guess they, like all of us, need more evidence then speculation, too.
Member Since: January 12, 2006 Posts: 5 Comments: 827
105. HurricaneMyles
3:57 AM GMT on April 02, 2006
Honestly, I'm not as impressed as you guys all seem to be. I think MichaelSTL put it well when he said the storms over the midwest look more impressive.

The flare up, to me, appears to be any other mid-level disturbance interacting with an upper trough. Like I said before, if this were June or later, a surface low could persist and out live the shear, but the shear simply wont relax enough during this time of the year for that to happen now.

I know everyone is anxious about the upcoming season, but it seems to me as though every little disturbance has been looked at as unprecidented. Its not unusual to see a few fair looking disurbances over the winter time. And unless I missed one, I think we've seen three.
Member Since: January 12, 2006 Posts: 5 Comments: 827
104. MZT
3:46 AM GMT on April 02, 2006
Those maps show shear to be fairly light off the Atlantic coast of Florida and in the Gulf of Mexico. So even this early in the year, if surface temperatures in those areas are warm enough, then....
Member Since: September 24, 2005 Posts: 0 Comments: 793
103. Levi32
3:37 AM GMT on April 02, 2006
Agreed HurricaneMyles, though it is interesting seeing something like this on the first day of April.
Member Since: November 24, 2005 Posts: 635 Comments: 26685
102. HurricaneMyles
3:24 AM GMT on April 02, 2006
If this was June or later, it might have chance to develope once the trough leaves the area and shear weakens. This is a similar situation to how Wilma developed, except the trough was over the whole Caribbean, not just PR. However, since this is April, and shear is not going to weaken, this thing has <1% chance. And If I hadent witnessed 2005, I'd give it a 0% chance
Member Since: January 12, 2006 Posts: 5 Comments: 827
101. RL3AO
2:29 AM GMT on April 02, 2006
looks like the shear will lighten very little, from dark blue to light blue ;)
100. DAVIDKRZW
2:18 AM GMT on April 02, 2006
Link


her is the forcast for shear for the next few days
99. Levi32
5:12 PM AKST on April 01, 2006
I have to go give the dog some time outside for a half hour. I'll be back as soon as I can this is very exciting!
Member Since: November 24, 2005 Posts: 635 Comments: 26685
98. Levi32
5:10 PM AKST on April 01, 2006
I agree, if the shear lightens to less than 50 knots, then I think it has a chance. I find it impressive that it is holding its own on radar. Very remarkable for being under 85 knot shear.
Member Since: November 24, 2005 Posts: 635 Comments: 26685
97. RL3AO
2:07 AM GMT on April 02, 2006
oh, sorry, I didnt read that right

I don't think they will unless this shear lightens up.
96. Levi32
5:05 PM AKST on April 01, 2006
I don't mean fly into it, I mean on their site will they name it an Invest storm which means a disturbance.
Member Since: November 24, 2005 Posts: 635 Comments: 26685
95. RL3AO
2:04 AM GMT on April 02, 2006
no, they wouldn't fly out if this was a Cat. 5. Because of its location, and its moving east.
94. Levi32
5:01 PM AKST on April 01, 2006
Do any of you think that the Navy will upgrade this disturbance to an invest storm?
Member Since: November 24, 2005 Posts: 635 Comments: 26685
93. RL3AO
2:01 AM GMT on April 02, 2006
so far, only one tornado reported

currently 2 tornado warnings in OK?
92. Levi32
4:57 PM AKST on April 01, 2006
Yeah they are sure firing up out there. Shaping up to be a long night for people in the plains.
Member Since: November 24, 2005 Posts: 635 Comments: 26685
90. Levi32
4:47 PM AKST on April 01, 2006
Maybe so.
Member Since: November 24, 2005 Posts: 635 Comments: 26685
88. Levi32
4:38 PM AKST on April 01, 2006
Here is another nice satellite loop. This also shows the remains of the cold front that could develope similar systems like the one we are dealing with now. The latest GFS shows what I mean.
Member Since: November 24, 2005 Posts: 635 Comments: 26685
87. Levi32
4:35 PM AKST on April 01, 2006
What I find unusual is that if there were favorable shear, this system would develope. That is rare to have a system with potential to develope so early in the year.
Member Since: November 24, 2005 Posts: 635 Comments: 26685
84. louastu
1:14 AM GMT on April 02, 2006
Any idea which direction that system will move?
80. NONAME4
8:00 PM EST on April 01, 2006
Ok then you should Find someone one that will endorse you and not have people argue because that just make some people frustrated and mad.
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79. grizzled
1:01 AM GMT on April 02, 2006
Indeed the low north of Puerto Rico has no chance of developing into a standard tropical system, it could develop into a low-atmosphere hybrid. The intense convection wrapped around the center is impressive.
On sea surface temperatures, please look at the latest NOAA anomaly mapLink
I think that most of the world's oceans are near-normal, despite all the global warming publicity.
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77. NONAME4
7:47 PM EST on April 01, 2006
Your tunnels would Damage the enviorment even more you also need to know the benfical factors of hurricane they help the enviorment. What doesnt help is man made stuff ruining the enviorment like MichaelSTL they are natural. You actully dont know as much as you think about the enviroment.
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76. NONAME4
7:17 PM EST on April 01, 2006
Cyclonebuster if you destroy hurricane it would cause problem also because they transfer heat from the tropics north and there upwells are very benificial to marine amimals.
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75. lightning10
12:22 AM GMT on April 02, 2006
I think we should all let the tunnel theory go. All its going to do is fire people up and then it will be flame war city.

Anyways how is everyone today? On another web site that deals with weather they have a total of 3.10 inches of rain coming for my area with 2-3 inches for most of Southern California. Looks like some of that subtropical moisture from the 50'th state could combine with a cut off low and slam the socal area with a lot of rain.

For the thunderstorms that might affect the area it should be interesting because I remember a situation a few years ago that looks like the one we might have on Monday. Where several areas reported small hail and a few areas around where I live reported a microburst. There was residual showers and thundershowers that lasted all day. Looks like it could be the big weather story this week.
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68. Levi32
2:49 PM AKST on April 01, 2006
There is a low level circulation with it on radar. This is very very interesting.
Member Since: November 24, 2005 Posts: 635 Comments: 26685
67. ForecasterColby
11:46 PM GMT on April 01, 2006
That low isn't anything right now, but shear is dropping over it, now only 60kt. With a break after the next front, it is possible, if highly unlikely, that we'll see Alberto live a day or two.
65. Levi32
2:44 PM AKST on April 01, 2006
Check out the 24-hour GFS. Look at that vort max ENE of Puerto Rico
Member Since: November 24, 2005 Posts: 635 Comments: 26685
64. Levi32
2:42 PM AKST on April 01, 2006
Check out the 24-hour GFS. Look at that vort max ENE of Puerto Rico
Member Since: November 24, 2005 Posts: 635 Comments: 26685

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