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

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

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.

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).

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

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",, 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. 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.

Reader Comments

Comments will take a few seconds to appear.

Post Your Comments

Please sign in to post comments.

Log In 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: 213 - 163

Page: 1 | 2 | 3 | 4 | 5Blog Index

205. louastu
6:42 AM GMT on April 03, 2006
Wow, I found 8 reports of 4.25 inch diameter hail.
203. louastu
6:31 AM GMT on April 03, 2006
There have been 613 severe weather reports so far, including 62 tornado reports.
200. louastu
6:24 AM GMT on April 03, 2006
Oh, well I was right earlier about the St. Louis area being in for it.
198. louastu
6:22 AM GMT on April 03, 2006
Where do you live?
195. louastu
6:15 AM GMT on April 03, 2006
I forgot to mention that around 5,200 people lost power in Indiana due to the severe weather.
193. louastu
6:06 AM GMT on April 03, 2006
Ya, pretty much. There were bad storms pretty much everywhere, just not Plainfield, Indiana. It was actually a little boring here.
191. louastu
5:27 AM GMT on April 03, 2006
Well, I just checked the preliminary reports. Turns out that there was a possible tornado touchdown within half a mile of several members of my family, a 60 mph wind gust near another relative, and an 82 mph wind gust in Indianapolis. This is all within 15 miles of my location. All I got was a brief downpour, 25-30 mph wind gusts, and a little bit of lightning. We were under a tornado warning for a little bit, but nothing happened here.

There have been several reports of trees and power lines down. Also, several windows were blown out of the upper floors of a bank tower (I think it was Regions Bank) in Indianapolis, and the winds caused the sprinkler system to go off.

Fortunately, despite all the damage, there have been no reports of fatalities, or any serious injuries in Indiana.
189. HurricaneMyles
4:46 AM GMT on April 03, 2006
Thanks Michael! I thought it was you who had the excact stat on when the last F5 was.
Member Since: January 12, 2006 Posts: 5 Comments: 827
187. HurricaneMyles
4:43 AM GMT on April 03, 2006
It's ironic, but as temperatures have warmed tornado intensities have seemed to decrease. There hasent been a F5 tornado in what...5 years, the longest stretch recorded without one? Not sure myself, but someone had the excact number around here.
Member Since: January 12, 2006 Posts: 5 Comments: 827
185. Robert876
4:28 AM GMT on April 03, 2006
CNN Breaking News - "At least eight people were killed when a tornado slammed into northwestern Tennessee's Dyer County"
Member Since: Posts: Comments:
184. Skyepony (Mod)
3:45 AM GMT on April 03, 2006
Looks like it was a bad line of storms... In the last 3 hrs it looks like some of the worst hit was~
NEWBERN DYER TN (1 fatality)
MILLSFIELD DYER TN (homes destroyed, injuries)
4 N HOPKINSVILLE CHRISTIAN KY (nurmous homes destroyed, gas fires)
FAIRFIELD WAYNE IL (widespread damage)
PIKE IN (widespread damage throughout county)
SOMERVILLE FAYETTE TN (damage/injuries)

Here's some highlights as to force of winds. Anyone want to guess intensitys?


There's a red trail of tornado reports drawing a line across NE TENN.

Storm Prediction Center(last 3 hours 186 preliminary reports)

509 reports since 6am
Member Since: Posts: Comments:
183. Robert876
1:25 AM GMT on April 03, 2006
First wave didn't miss them, they still have a long way to go.
Member Since: Posts: Comments:
182. RL3AO
1:08 AM GMT on April 03, 2006
this first severe cell will miss the south side, but the squall line will be there soon
Member Since: Posts: Comments:
181. Robert876
1:02 AM GMT on April 03, 2006
Opening Day for Baseball, and there about to go into a rain delay once the rain picks up.
Member Since: Posts: Comments:
180. hurricanechaser
10:38 PM GMT on April 02, 2006
Hey everyone,

I managed to find some time last night and today to finish my very extensive hurricane research into all direct landfalls on the U.S. coastline for the period of 1950-2005, that I will outline in great detail in a four part blog siries as time allows.

That being said, I have just posted Part One of this series focusing on all the La Nina hurricane landfalls categorized by the three AMO cycles that influenced hurricane activity during this period, as well as specifying each hurricane landfall by individual State and geographical locality.

Please see the link below for full details into the aforementioned data, which should help all of us better understand our Hurricane history as well as our vulnerability for furture hurricane seasons that are impacted by the "La Nina" phase of the ENSO cycle.

Naturally, we are currently in the La Nina phase of the ENSO cycle which is most likely to influence this upcoming Atlantic hurricane season.:)

I hope everyone has a great day and a good upcoming week.:)

Your friend,

Member Since: Posts: Comments:
179. Levi32
2:28 PM AKDT on April 02, 2006
The storms are moving through St. Louis very fast. They are almost past.
Member Since: November 24, 2005 Posts: 635 Comments: 26780
178. Levi32
2:22 PM AKDT on April 02, 2006
Looking really dangerous for St. Louis metro. I hope no tornadoes go through a crouded part of town
Member Since: November 24, 2005 Posts: 635 Comments: 26780
177. RL3AO
10:15 PM GMT on April 02, 2006
St. Louis is getting pounded right now

St. Louis county is under a tornado warning
Member Since: Posts: Comments:
176. RL3AO
9:18 PM GMT on April 02, 2006
its about 60-80 minutes from you
Member Since: Posts: Comments:
174. louastu
8:44 PM GMT on April 02, 2006
That doesn't look good for you.
172. Skyepony (Mod)
8:10 PM GMT on April 02, 2006
As far as DST, they are slowly starting it earlier. A few years ago (as it had been for at least the last 25 years) it began on Easter Sunday. Making it sooner has been an energy conservation issue, which I'm glad to see it come to pass. My general observation (& I'm sure there are exceptions:) Morning people prefer SDT, night owls like DST.
Member Since: Posts: Comments:
171. lightning10
6:10 PM GMT on April 02, 2006
Hi friends first I would like to say I dont like daylight savings at all. I like the dark.

Anyways looks like I might have jinixed the storm that is coming toward the south west...

"The GFS continues it's trend in keeping the main upper low a bit further north than the NAM, and the nam's precipitation output is a half inch to one inch lower than earlier runs"

That tells me that most of the heavy rain and thunderstorms will stay north. It sounds like the last storm. I wouldnt be suprised if they downed the rain fall totals to 1-2 inches.

On the satellite imgae and the water vapor image last night it didnt look very impressive.
Member Since: Posts: Comments:
170. HurricaneKing
6:03 PM GMT on April 02, 2006

I'm in the 30%
Member Since: Posts: Comments:
168. grizzled
5:54 PM GMT on April 02, 2006
Oops, I'll try again


Looks like the tropical Atlantic has cooled a bit versus last year at this time
Member Since: Posts: Comments:
167. grizzled
5:50 PM GMT on April 02, 2006
Looks like Global Cooling may be underway

Oceans have cooled noticeably since this time last year
Member Since: Posts: Comments:
5:41 PM GMT on April 02, 2006
: MichaelSTL help help help in my yahoo e mail
5:34 PM GMT on April 02, 2006
did Daylight Savings Time come a little bit eary for any of you to where it sould be for

Viewing: 213 - 163

Page: 1 | 2 | 3 | 4 | 5Blog Index

Top of Page
Ad Blocker Enabled

Category 6™


Cat 6 lead authors: WU cofounder Dr. Jeff Masters (right), who flew w/NOAA Hurricane Hunters 1986-1990, & WU meteorologist Bob Henson, @bhensonweather

JeffMasters's Recent Photos

Lake Huron
Fall Color in Pictured Rocks
Pictured Rocks Beach Day
Pictured Rocks dunes and clouds