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Global warming and hurricanes part 1: The natural cycle

By: Dr. Jeff Masters, 7:39 PM GMT on December 19, 2005

Before we can discuss the possible influence of global warming on hurricanes, we need to set the stage by talking about this natural cycle of hurricane activity we hear so much about. The Atlantic Multidecadal Oscillation (AMO) is a cyclic variation in the large-scale atmospheric flow and ocean currents in the North Atlantic Ocean that combine to alternately increase and decrease Atlantic sea surface temperatures (SSTs). As its name indicates, the AMO is "multidecadal"--meaning it operates on a time scale of multiple decades. The cool and warm phases last for 25-45 years at a time, with a difference of about 1�F (0.6�C) between extremes. These changes are natural. Analysis of tree rings, fossil coral, and sediments has shown that the AMO has been around at least 300 years, and probably much longer.

What has the AMO done in recent years?
As seen in Figure 1, the AMO has been though about two complete cycles since detailed measurements of the Atlantic began in the mid-1800s. A cool phase lasted 25 years from 1901-1925, a 44-year long warm phase from 1926-1969, and a 25-year long cool phase from 1970-1994. A new warm phase began in 1995, and the AMO index values since 2001 have been the highest on record. This has resulted in sea surface temperatures over the prime hurricane breeding grounds of the tropical North Atlantic being the highest on record, as well. The AMO index in 2004 was about the same as in 2003, but 2005 has seen about a 10% drop from 2004's level.

Figure 1. The AMO index, 1871 to 2003. The index was computed by averaging sea surface temperatures north of the Equator over the Atlantic Ocean, between 75�W and 7.5�W and south of 60�N. The red regions show warmer than average SSTs over the North Atlantic, and the blue regions, cooler than average. The "trend" has been removed, so the mean and long-term increase in SSTs are not visible. Image credit: Rowan, T.S., and Daniel Hodson, "Atlantic Ocean Forcing of North American and European Summer Climate", Science 309, 115-118, 2005. Reprinted with permission from SCIENCE, � 2005 AAAS. Permission from AAAS is required for all other uses.

How do hurricanes vary during warm and cool AMO cycles?
The AMO is thought to strongly influence the incidence of intense hurricanes, which more than double during the years when the warm phase of the AMO. For example, an average of 1.5 intense (category 3, 4, and 5) hurricanes per year formed in the Atlantic during the last cool phase of the AMO, 1970-1994, while 4.1 intense hurricanes/year formed during the current warm phase (1995 - 2005). The number of tropical storms and weak hurricanes do not change much between cool and warm AMO periods.

What causes the AMO, and can we predict it?
The causes of the AMO are not well-understood, but some "coupled" computer models that simulate the behavior of both the atmosphere and the ocean are beginning to shed light on this. One of the leading theories is that changes in the ocean's salt content causes a speed up or slow down of the Gulf Stream, due to the fact that density differences between lighter fresh water and heavier salty water drive weaker and stronger ocean currents, respectively. This circulation (called the "thermohaline circulation") is thought to cause the warm phase of the AMO and warmer Atlantic SSTs when it speeds up, and cooler SSTs and a cool AMO phase when it slows down. It is also possible, but less likely, that changes in atmospheric circulation cause the AMO. We are a long way from being able to predict when a particular phase of the AMO will begin or end. The last warm phase lasted for 44 years. The current cycle began in 1995, so it may not be until 2040 that the current active period of hurricane activity dies down.

What influence does global warming have on the AMO?
Since the instrument record extends back for only two cycles of the AMO, it is difficult to say if the record warmth in the current AMO cycle is unusual. It has been observed that the tropical North Atlantic SSTs have warmed approximately 0.3�C over the past 100 years due to global warming. However, the current thinking of climate experts is that global warming should act to dump increased fresh water into the North Atlantic and reduce the speed of the Atlantic thermohaline circulation. This would lead to a decrease in Atlantic SSTs, and a reduction of intense hurricanes. Either global warming hasn't acted to dump enough fresh water into the North Atlantic to affect the thermohaline circulation, or else the theory is wrong!

Jeff Masters

Climate Change

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Reader Comments

Thanks Dr Masters. ALWAYS Tremendously Informative & Compelling.

Great post Dr. Masters. Thanks a lot for your work!

Thanks Dr. Masters. The more I read about global warming and the various theoretical causes and effects, the more confusing it all seems. One thing that occurs to me is that if global warming was due to human activities, we would see more dramatic increases and decreases in the different measurements of climate change. I am looking forward to the next blog!
i am back on my blog and it have been update and will have one more up dat at 3pm and may be 9pm or 10pm and a very big storm comeing to ca and i will have more on this at 3pm so come on by and take a look
To get the NHC Epsilon report go to www.nhc.noaa.gov/,
look under "2005 Season Summaries and Reports",
& click on "Tropical Cyclone Reports".
Looks to me like the Cycle which causes an increase in the intensity of these hurricanes also changed the loop current. As you said, compared to 12 years ago, there has been a 30% reduction in the loop current...and when did this last Cycle 'start'? about 10 years ago... Hard to really know if the melting ice of the north pole is inducing this 30% reduction or its just the cycle we are in.

Very intersting stuff there Jeff Masters. THanks

Dr. Masters...

Many events leave perment "scars" on our earth. Has there ever been studies of our coast lines to see if there has been a long history of storms like we have seen in the last couple years? Like forest growth, shoreline reconfiguration, ect?

And also mother nature destroys herself cause she knows better then we do..is there any chance that by replacing and protecting the shores from damage that we could be damaging the "plans" mother nature has? For proof look at the island the AE just recently built. With in weeks they noticed a slight shift in temps and currents on the opposite side of the Persian Gulf. Just a thought.

Thanks for an awesome Blog.
look at this from the W storm

An unconfirmed report gave the minimum central pressure as low as 26.00 inches of mercury (880mb
hey KRWZ how are you?

where did you get that report from?
RMH, i personally dont really think coastline restoration works. I was reading something the other day talking about how they were going to restore 12 miles of this river. That sounds all fine and dandy, however the river is almost 1000 miles long. Now its nice that they are restoring it, however what will 12 miles out of say 500 miles of ruined coastline or riverway do? I say stop as much contaminating etc. as possible, and START TODAY!!!
KRWZ, I don't doubt you. In fact, I personally think it was 868-875 MB, based on the rate of intensification and the satellite presentation.
What is the relation to AMO and NAO (North Atlantic Oscillation) which has to do with winds?

I suppose it's critical where AMO is measured. If THC speeds up, SST from the equator towards Greenland will become more uniform. But it also means the downwelling process is getting significicant frigid cold, saline water.

If THC slows down (warmer, fresh water at the downwelling spots) then less tropical water will be drawn north. So the tropical water will tend to be warmer, and the extratropical water will be cooler.

Good writing on a critical subject.
TORN, how are you?

i wasnt questioning him or the report if thats what you thought i meant, i just wanted to ask where that report came from because the official minimum central pressure stands at 882mb. i also happen to agree with you as i believe in the 4-5 hrs that recon was not in wilma (while it was still intensifying on the morning of october 19th), that its pressure was between 873-879 mb and her winds were in the 180-185 mph range.
hi atmosweather

hi tornadoty

how is ever one tonight?
thanks, KRWZ

atmosweather try this one that was not the right one sorry for that it may say 1935 hurricane but on it it says a little bit about the W storm i hop you can find it
"The storm formed east of the Bahamas in late August and traveled due west through the islands. It then began a gentle turn to the northwest and headed straight for Islamorada in the Upper Keys, where it struck on Labor Day, Monday, September 2 around 8 p.m. The winds at landfall were originally thought to have reached 160 mph, but, reanalysis studies conducted by the NOAA Hurricane Research Division (HRD) have concluded that maximum sustained winds were as high as 185 mph. A central pressure was reliably reported as 26.35 inHg (892 mb). This was the record low pressure for the Western Hemisphere until it was surpassed by Hurricane Gilbert in 1988 and Hurricane Wilma in 2005. An unconfirmed report gave the minimum central pressure as low as 26.00 inches of mercury (880 mb)."

Actually they are talking about the minimum central pressure in the Labor Day Storm of 1935, not Hurricane Wilma. The 880mb report was probably unreliable from observations near the Keys at the time of the Labor Day Storm's landfall.
hey whats up
so winds in the W storm was 185mph at one time right atmosweather ?
hey theboldman where did your bolg go now?
atmosweather why is the nhc takeing a long time to do there updat on this year hurricane year


i would like to see what they will do with the E storm and K storm to see if they have updat the E storm to cat 5 to make it 4 cat 5 in a row wow and the K storm to see if they will update it to a cat 5 at landfall and to see what they will do with R and W storm to see if they will keep it at cat 3 at land fall or updat them to a cat 4 at landfall with R and W
where did ever one go?
no home maybe the all went out for a pizza can i have some?
I'm here, KRWZ

I know the nhc are taking a while this year, but look how many reports they have to write!!! And, like we have all said in the last few weeks, they have so much to revise and look at from the past season. They have so many statistics from storms in question and post-storm analysis from 6-8 storms takes a long time. I say we all should be patient and let them come to the right conclusions about every one of them. Remember, they are taking their time because if they make changes to storms, then all of those changes go in the record books forever, and cannot (should not) be altered. They are determining the final chapters in the books of these storms which will go down in history, so I encourage them to take their time and get their analysis right.
I am glad Dr. Masters is talking about this issue!!!!Hopefully we will get some facts that u guys agree on & then hmmmmm will my "liberal" views be questioned or not?????????
heres my part in this global warming thing

i will still drive my tractor with pride =)
LOL fshhead. You are entitled to your "liberal" views, just like I am with my "conservative" ones! But this is not an issue on liberal/conservative views. This has to be taken very seriously. Imagine the outcry if scientists did prove that global warming leads to increased natural disasters AND is caused by humanitarian ignorance?
LOL boldman. That's the spirit!!!!
i got you now atmosweather when do you think they will be down with it?

hey theboldman where your blog a few days ago it was there now it is not
They will start coming in this week and the weeks after Christmas and new years'. I expect the less controversial storms (i.e not Katrina, Wilma, Rita, Cindy, Emily, Delta ect. which are the ones they are conducting intense post-season analysis on) to be done first, perhaps the less damaging and shortest cyclones (Lee, Gamma, Franklin, Harvey ect.) maybe by the end of the week. I have no idea when the likes of Emily, Katrina, Wilma, Rita ect. (the ones we want to know!!!) will be done; they could take a long time since each of those storms are going through a ot of reanalysis and research. I am sending an email to one of the forecasters at the NHC right now to ask them how far along they are in their post-storm analyses.
Atmos..... everytime I post what I think are Facts.... Someone comes along calls me a liberal & tells me to move here there & everywhere LOL I agree that it is not liberalconservative issue but a "human" issue.
david my blog is up lol
Ah, Dr. Masters, the more we seem to learn the more questions seem to arise! Thank you for all the info!
atmosweather when you do ask them if they have update the E storm to a cat 5
I completely agree fshhead, unfair to be treated like that anytime but especially when the issue at hand is nothing to do with politics

KRWZ, if they knew the answer to Emily's strength I they would have completed her post-season report by now. I am just asking them how close they are to finishing some of the reports
atmosweather i got it

theboldman my favroite Christmas movie is narnia and tell me that the movie narnia is not a Christmas movie
atmosweather did you see narnia yet i have i have see it 4 times now
40. F5
The only thing we know for sure is that all ability to model the atmosphere and oceans is woefully inadequate. Pieces of the puzzle can and do fit some times, and other times, couldn't be more wrong. And that's without trying to account for whether or not humans are influencing weather in one capacity or another.

Frankly, IMO, and discussion about greenhouse gasses et al, should focus more on the pollution aspect than the weather aspect. We have the ability to accurately measue pollutants in the air, and the effect they can have on the lungs. That is the angle to attack, not CO2 from human activitity causing global warming or running out of oil. For years, chicken little has been running around claiming the world is on the brink of running out of natural resources. There's likely more oil and gas still in the ground than the sum of all that has ever been used. The question becomes one of extraction, not depletion.

Another blog talked about alternative energy resources. Frankly, nothing is likely to happen until the cost of oil becomes prohibitive. Then, you will likely see investment in alternative energy sources. After all, necessity is the mother of all invention. Until then, you can count on business as usual.

Potential alternative energy sources...

Hydrogen fuel cells

There may be others, I haven't kept up on all the latest.

I'm no engineer or scientist, but if we can use an electrical force to generate a magnetic force as in a coil, then why can't we do the reverse? Why can't we use a magentic force to generate an electrical force?
good night ever one and by the way have any one see hurricanechaser im the last few day i hop he is doing ok and his 4 year old is doing ok as well
have a good night KRWZ

i'm off to bed as well. hope everyone here has a good night

You can use a magnetic force to generate an electrical force.
That's how a generator works. For example, wind from a
hurricane turns the blades of a windmill. This spins a magnet
inside a coil of wire. This generates a voltage in the wire.
See "Electromagnetic induction" in Wikipedia for example.
44. Inyo
There's likely more oil and gas still in the ground than the sum of all that has ever been used.

entirely possible..

but it seems to me... right now we arent sure to the extent we affect the 'greenhouse' warming of the earth (the greenhouse effect exists regardless of humans, we just may intensify it)...

but anyway.. if there really is that much oil, and we burn it all, then i feel very strongly that it will have a large effect.

that isnt to say reducing pollution isnt.. it is. It won't matter what temperature it is if we all die of cancer.
Evening all. Hope everyone is well.

Want to take a moment to thank everyone that provided so munch information this season in WHATEVER fasion it was.

There were a lot of debates and arguments, but I hope that everyone learned somthing from each one of them. Emotions and personalities aside,I know I did.

I will be dropping in all winter, but to those that won't...THANKS! This goes for everyone.

Still working on my site. Stop by from time to time.


Also looking for good links to video from storms. The stuff we are not seeing on the national networks. Also any other good tropical links would be great. I have started a blog geared around this so if you have them please post them there.
There's likely more oil and gas still in the ground than the sum of all that has ever been used.

I recommend you read "Hubbert's Peak", by Deffeyes. A pretty good review of everything you ever wanted to know of petroleum geology, and how reserves are estimated. Complicated subject, but the takehome message is that we are probably right now at, just past, or within a few years of peak world petroleum production, and production will be declining from here on.

I'm no engineer or scientist, but if we can use an electrical force to generate a magnetic force as in a coil, then why can't we do the reverse? Why can't we use a magentic force to generate an electrical force?

As gippgig responded, that is exactly how a generator works. This doesn't give you a source of energy, however, just a means to manipulate existing energy.
47. F5
Yes, but generating the rotation of the electro-magent requires some other energy source for it's movement, which then generates the electrical force. If you could find a way to manipulate the magnets into rotating without having to use an alternate source of energy, that's what I'm talking about. Or, at least so that the output would be greater than the input, so that it becomes a self-sustaining energy source. I guess that's why we don't have perpetual motion machines...

As for whether or not we are past the peak of production, it may be true, but not, because, the oil isn't there. More likely will be that the cost of extraction exceeds what the demand will be willing to pay per barrel. This in turn, will drive demand towards alternative energy sources.

I am no fan of government, but if they are going to use our money for stuff I don't want them to use it for, then lets at least get them to do some serious funding of alternative energy resources. Again, I think the focus should be on the pollution aspect, not the nebulous "global warming", which we can't effectively model and prove.
48. Inyo
the thing about global warming is that maybe there's a 50/50 chance of it causing us problems (that number is up for debate of course)... if we cut down on oil consumption, it slightly weakens our economy in the short run but it also reduces our dependance on the Middle East, even if nothing happens. If we ignore it, and it turns out that it IS as bad as some people think, we are going to have major problems. It seems logical that we should think in the long term but people usually don't.

Also, like some of you said, there may be a lot of oil left. However, 'we never ran out before, why would we now' doesnt make much sense.

anyway this is off topic, but i am just waiting for the high to break down.
"Many events leave perment "scars" on our earth. Has there ever been studies of our coast lines to see if there has been a long history of storms like we have seen in the last couple years? Like forest growth, shoreline reconfiguration, ect?"

Sure, people find evidence of pre-historic storms all the time. I did my grad school field work on the Delmarva peninsula, which is basically a big sand bar. As you dug through the sand, you would come upon layers where instead of medium-grained sand, suddenly you had lots of pebbles, large shells, etc. These layers were overwash from old storm events.

I don't know if you would be able to determine how these old storms compared to recent ones, however. The climate was so different; these storms happened tens of thousands of years ago, during and between ice ages.
Sounds a little scary for the Florida Keys at least for the next 35 years. Maybe I should move back to Syracuse and fish 4 months out of the year? No, I think I will risk it and just get out of the way when they come.

Good afternoon everyone,

The National Hurricane Season have issued their final report on Hurricane Katrina and have decided to downgrade Katrina's landfall intensity in Buras, LA to 110 kts, or 125 mph (Category 3 strength). They have also reduced Katrina's maximum sustained winds at landfall in MS to 105 kts, or 120 mph (Category 3 strength).
Excuse the typo, that is a measure of how angry I am with that decision
: atmosweather what? cat 3 at land fall not cat 4 at land fall may be they sould take a look at the photo one more time do not think a cat 3 hurricane can do that i think it was a cat 4 at frist land fall with 145 or 150 mph and 130 or 125 for the 2nd land fall so i think the nhc sould take a look at some photo from that storm one more time to see iif that is right and did they up date the winds when it was a cat 5 storm at one time or did they keep it at 175mph winds?
Guys, take a deep, long breath before you get angry.

There are two reasons that you should not be angry with this decision:

1. The wind field did expand wildly from 90 miles to 125 miles, and the intensity given in the report is probably proper

2. If you read the report, then you will notice a paragraph that says that there is a good chance that cat. 4 winds reached the coast, thus possibly making it a cat. 4 strike, but a cat. 3 landfall.
tornadoty so it was a cat 4 at 1st land fall not a cat 3 at 1st landfall
hey did you all note that the Tropical Cyclone Reports from the K storm is not there no more where did it go?
Hey everyone,

I hope you are all doing well. I noticed that the NHC had the Katrina report that Rich (Atmos) alluded to earlier on their website. However, it's no longer there at the time of this writing. I wonder why they removed it. I guess we shall see soon enough. I find the downgrade ridiculous and their explanations to be very unconvincing as well respective to the extreme storm surge for instance. In other words, it needs to be removed and revised to reupgrade Kastrina back to at least a 115 knot..135 mph category four hurricane at Buras landfall in SE La.

I also noticed that their report even listed the Forrest counties EOC wind reading as Forrest, Mississppi when in reality it should read South Hattiesburg, MS. because that's the location I filmed the storm only 0.1 miles away from this building. In short, all they had to do was transfer this information directly from the Jackson, MS. NWS report and they couldn't even do that right.

Anyone wanna guess how I feel about the report?

Regardless, I hope everyone is doing well and I will continue to update my blog on the Global warming issue throughout the week.


KRWZ, it was a 125 MPH category 3 hurricane at its 1st Gulf Coast landfall. What the NHC is saying is that the norhtern eyewall may have had category 4 winds when it hit LA, but when the eye made landfall, the maximum intensity was category 3.
Hey Tony (hurricanechaser), did you get to read it?
I just read a couple new posts that were added while I was writing my previous one. Therefore, I thought I would add one further note to the discussion.

It's important to realize that it is highly likely that Katrinas strongest winds weren't sampled as ws the case with Andrew for instance. In very intense hurricanes such as these, it is very difficult to build a detailed wind field observation since most can't survive the storm. Likewise, the ones that do still may not sample the strongest winds especially in a storm like Katrina when her structure was changing at landfall. Moreover, the anemometers all throughout he coastal areas were disabled by storm surge in many cases well before they could obtain any significant wind measurements.

My central point is that all of our collective opinions regarding hurricane Katrinas true landfalling intensity is left to some subjectivity on those analyzing the data including those who wrote the report.
hey : hurricanechaser where have you been did you get my two e mail?
the Tropical Cyclone Reports from the K storm is back what see what they update lol
63. TBA
I always thought that basing landfall on the center of a hurricane, was a bit foolish. A hurricane could skirt the coast with high winds from the eyewall, then veer off to sea, and the official report would say that the hurricane never really made landfall.

Landfall should be defined as when the eyewall makes landfall, not the calm center of the storm.
Hey Tony and David,

I did get to read the report thoroughly, but I didn't think it was very well written to be completely honest.

My suggestion is that Katrina was most likely a landfalling 135 mph category four in La. and a 125 to 130 mph category three at Mississippi landfall.

I must add that the downgrade didn't surprise me given the HRD's desire to make her a 115 mph category three at Buras and a 95 mph category one at Mississippi landfall. Therefore, I have to admit that I was more surprised that they only reduced the Mississippi landfall by an unremarkable 5 mph and kept it as a strong category three.

This actually supports my suggestion that Katrina was most likely a 135 mph category four at Buras,La., although I can't prove it and neither can anyone truly prove otherwise. That goes back to my initial comment regarding the subjectivity of the individuals making the determination.

I made the appropriate changes on my blog.

Hurricanechaser, I think that if the fact that it may have had 135 MPH winds on the LA coast before landfall was important enough to bring up, then I agree, it should be a cat. 4 landfall, like TBA suggested.
I hope everyone has a great night and a very merry Christmas in case I don't get to talk wih you again between now and then.

Hey david,

I did receive your email and I was going to respond after I posted. I really appreciate your thoughtfulness and asking about how my family and I are doing. I also hope you and your family are doing great as well.:)
hurricanechaser did you het my 2nd e mail too?
I agree that both TBA and yourself make excellent points and I couldn't agree more. If a location gets category four sustained winds as noted in the report, how can they say that that area only received a landfalling category three strike. Both Hurricane Emily in 1993 as well as Alex last season brought their respective NW eyewalls ashore along the N.C. Outer Banks and both are considered landfalls. For Emily, she is listed as a major hurricane strike when her maximum intensity was 115 mph and those winds never reached the coast. For alex, they took the estimated sustained winds that most likely occured and listed this 100 mph category two hurricane at the time as a 80 mph category one landfall. My problem is with such inconsistency. Based on these two examples and the NHC report for Katrina stating that it's likely that a small area of the extreme SE La. coast received sustained category four conditions that there should be no reason that she isn't listed as a category four landfalling hurricane.
Can you send feedback to the NHC? And more importantly, would they read it?
Hurricane chaser I emailed you...
To be more specific..I don't think it matters to those in its direct path if the NHC says they only received a category three strike when they lost their loved ones and homes to a large category four. In other words, they can say she was a landfalling category one storm and it still wouldn't make it true. These residents who bore the absolute brunt of Katrina got hammered by a landfaling category four and writing a report saying otherwise can't change that reality. However, I think it's more of an injustice to these who did receive those sustained category four conditions for the official record to say otherwise. If you are going to err in such instances, I think it's best to go the other way.

Just think about it, we now have Katrina making landfall as a 920 mb category three with 125 mph sustained winds that will go down in the official records as hurricane Wilmas landfalling 125 mph winds when her lowest presure was 950 mb at landfall. That is a full 30 mb difference. Naturally, I am aware of the pressure gradient that creates such winds, but, I find it hard to reconcile a 920 mb presure with a 125 mph moderate category three storm.

The Missisppi landfall comes in at a 120 mph 928 mb hurricane that produces a 27 to 30 foot storm surge. Now that definately sounds logical. I read the NHC explanation for this huge surge and it was very unconvincing to put it mildly. The suggestion was that this is typical of a large category three hurricane that was a category five less than 24 hours prior to landfall which created a large wave setup. It is important to realize that the storm surge is the level of water rise above normal sea levels that doesn't consider wave setup nor their heights. That's why the look for still water marks on buildings rather than the highest water marks which are caused by the wave action. On the other hand, I by no means want to denegrate the catastrophic consequences that such wave action has caused to life and property and will do so again in the future. However, the historical record has to be accurate and that explanation doesn't hold water in my opinion (pun intended).

Hey Tony,

I have written the NHC about my wind observations for hurricanes Katrina and Ophelia and received a direct response. In addition, I also received a response from them regarding my lenghthy blog detailing why I believed that it would be a huge mistake to take the HRD's advice and downgrade Katrina to a 95 mph category one at Misissippi landfall. They will read it and respond.:)
Hey Katie,

I just read your email and I greatly appreciate your kind words and thoughtfulness as always.:) I hope you are doing well. I will write you at some point during the next couple of days. I have done a poor job of replying to emails as of late I'm ashamed to say. However, I fully intend to reply to each one of them this week, especially to wish each of you a wonderful and very Merry Christmas.:)

Honestly, I have been so busy with work that I barely can find time to add an additional paragraph or two to my curent blog that I am still in the process of writing.:)
Dr. Master's observes:"Since the instrument record extends back for only two cycles of the AMO, it is difficult to say if the record warmth in the current AMO cycle is unusual."

In my exerience analyzing time-dependent signals, I would have to go further and add doubts that this can even be properly called a cycle, especially since causality is in doubt. After all, we have only sampled two cycles, and I would imagine we have increasingly less confidence in the data the farther back in time we go. In other words, there is no way of knowing whether the mean temperature will remain constant averaged over the next ~140 years, as compared to the average shown in the graph. The mean may increase or decrease, the period of the "cycle" may change, or there may not be any more cycles in the next ~140 years.

I will be very interested in Dr. Master's explanation in his forthcoming blog. If there is strong evidence for a mechanism that causes cyclical behavior, my doubts would be lessened considerably.
Hey Katie, Tony, and David,

It was great talking with each of you again and I hope I get the pleasure to do so again in the very near future. I need to get some things accomplished around my house. :)

I hope each of you and all others who will visit this blog after I leave, have a wonderful night.:)

Thanks again,

76. Inyo
I understand why some people might disagree with the hurricane being downgraded but i don't understand the general anger that comes about when someone suggests it may have been weaker at landfall. If it hit at marginal cat 3/4 as opposed to 5, this doesnt mean that it lessens what happened to the people in their path. Instead, it just points out even more strongly that THIS WAS NOT THE WORST case scenario at all, and we are woefully unprepared for hurricanes as the coastline becomes more developed and their frequency and intensity appear to be increasing, at least for now.
Hi everyone sorry to go off Topic but I have always wanted my city to be the hottest city in the USA. We where so close today. It was 80 here in Whitter,CA today where I live. The hot spot of the nation was 82 degrees at Ramona, Calif. Its the ugliest 80 degree day here I have even seen. Real pore air quality do to high pressure along with mid and high clouds over the area.
Katrina was far from the worst case scenario. It was actually almost the best case scenario for a major hurricane hitting New Orleans. Only a little over 1000 were killed. If the
storm had veered to the west instead of east the storm surge would have demolished the city killing 10,000+. If the levees hadn't failed very few would have been killed - but the next time a category 4+ hurricane hit the city many people wouldn't
heed the warnings & 100,000+ would be killed.
Great information Dr Master. I like learning about this stuff. Hello to everyone and Merry Christmas, Happy Haunkkah, and everything else. And may you have Peace, Prosperity, Health and Happiness in 2006 (an no hurricane's hitting us!)

Hey everyone,

I thought that I would post one more comment before I call it a night.

First of all, my sentiments of disappoint about Katrina being downgraded is the fact that I strongly believe that she wasn't categorized properly and for many of the victims that were afffected by this devastating storm feel that it is an insult that they lost everything they have to a large category four hurricane only for those who have no choice but to use subjectivity due to the lack of reliable wind data decide to downgrade the storm to a moderate category three.

In other words, I take it pesonally because I have family that lived through this storm and they are upset abnout it. Moreover, this is the prevailing sentiment from a few people I have talked to about this that I met while covering the storm myself. It is the equivilant to some of being told you only had gotten over the common cold when in fact you were fortunate to recover from pneumonia.

So is it better for the person to be told they have the common cold when they are battling pneumonia so that they will realize how much worse it could be if they get an even worse case of pneumonia. In other words, I have heard the argument that is shouldn't matter if the storm is clasified as a weaker storm because it will just help more people become aware of how truly dangerous a real category four could be. Although I understand the logic, I still disagree with the perspective as do those I have talked to that truly experienced the event themselves. Who am I or anyone else to tell those who lost their home or even worse a loved one that you should feel fortunate because it could've been much worse. For them, that is no consolation nor should it be.

No one truly disputes that Katrina was by no means the worst case scenario for the New Orleans area or anywhere else. On the other hand, it was the worst case scenario for more tan 1200 people who lost their lives and the loved ones who will forever mourn their loss. So I don't believe it's appropriate to talk about how only a little over a thousand lives were lost when it could've been thousands more. If one person loses their life as a result of any storm regardless of its intensity, we should show respect for that one life cut short because it was someones loved one or friend.

I hope that all of the aforementioned we help some understand why I feel so strongly about this downgrade that I personally feel is not justified by the incomplete and limited wind data, massive storm surge, and the incredible inland wind damage that I saw first hand. In short, I believe it is an injustice to those like my family and friends who lost so much as a result of this storm for the NHC to downgrade this storm a full category when it came down to a subjective analysis when it would've been best to leave it the same than make il advised changes.

i think the nhc need to go over the update one more time i think they sould update her to a cat 4 or may be low cat 5 at fris land fall and then for 2nd land fall a high end of a cat 4 or a low rend have a cat 4 i think i will e mail the nhc and tell them that do you all think a cat 3 hurricane can do that march? lol
not a happy day lol with the nhc and i will e mail them and tell them that not a happy day i was hoping for a update of winds to a cat 5 at land fall not a cat 3 at land fall like the A storm back in 1992 and that was update to a cat 5 at land fall and did 26.4 B why the K storm did 100b and it is not up date to cat 5 storm all lol on the nhc for a not happy day lol
Good evening everyone. I am going to be writing a few blog entries tonight and tomorrow about controversial topics such as the Hurricane Research Division and the ENSO, so everybody is welcomed to read my views and share your own with me. However, I would like to say something about the National Hurricane Center's Final Report on Hurricane Katrina:

Having lived in Florida for 15 years of my life, I have on many occasions witnessed the power of a hurricane making landfall. Additionally, I have many friends and family that live in Mississippi and Louisiana, some of the worst affected areas of the 2005 Hurricane Season. Now, I could be biased and let this affect my judgements on the National Hurricane Center and the Hurricane Research Division. However, despite much of my family and a large number of my friends having been directly impacted by Hurricanes Katrina, Rita and Cindy this season, I am going to try and forget this and still give my views on the National Hurricane Center's final Katrina report. I would like to point out that I realize how little this will affect people who have been displaced by Hurricane Katrina. However, I still have very strong opinions on this subject. It is important, I think, to properly gauge the true intensity of Hurricane Katrina as it impacted our shores. By the way, I have read every single word of the final report twice, so I didn't miss anything if you are wondering.

I will start off on a positive note for the National Hurricane Center: I believe after looking at endless loops of Katrina and recorded wind and pressure reports, that the intensity judged by the National Hurricane Center when Katrina made landfall in southeast Florida is entirely accurate. The values of 70 kts (80 mph) and 984 mb seem extremely plausible and I credit the National Hurricane Center for being right on the money at Katrina's first landfall in Florida. Now, I would like to share my opinion on Katrina's final two landfalls, in Buras LA and on the MS/LA border. First of all, I will comment on Katrina's satellite presentation from time of peak intensity (1800 UTC August 28) until final landfall on the MS/LA border (1445 UTC August 29). There is no doubt, and many if not all of you will agree with me on this, that Katrina's satellite presentation in the 21 hours from peak intensity to her final Gulf Coast landfall was on a downward trend. Hurricane Katrina without question had weakened while approaching the northern Gulf Caost.

This brings me to my next point. In the National Hurricane Center's final report, the author mentions an unpublished study on the 11 hurricanes in the last 20 years with central pressures below 973 mb 12 hours before landfall on the northern Gulf Coast. The National Hurricane Center states that all 11 of those storms weakened significantlu in the 12 hours before landfall (Ivan and Dennis are 2 recent examples). By mentioning this type of study, it makes me wonder that because there was so much post-storm analysis with Katrina and they took such a long time to come to a decision about Katrina's landfall intensity, that they decided to base their final report measurements on their own study. I am not accusing them of anything, but if the real reason for Katrina's downgrade was because they didn't have a case to change her intensity and so decided to use climatology (which is only 20 years of studies and obviously very separate condition sets for each hurricane) to downgrade her just like the previous 11 hurricanes had weakened in the same position, then I have a serious problem with their decision. There is no sane explanation for doing that in any case. Hurricane intensity should NEVER be judged on climatology since there is so much data accompanying a landfalling hurricane in the United States (or anywhere in the world for that matter) to make an educated guess AT WORST on a tropical cyclone's intensity. In fact, it makes me wonder also how with so many satellite estimates, buoys, reporting stations that they couldn't at least prove their case for downgrading Katrina.

Almost all the reasons provided by the National Hurricane Center for the downgrade of Katrina are based on dropwindsonde, doppler radar and aircraft data. Well, it is a proven fact that neither dropwindsondes or reconaissance aircraft can accurately measure surface winds with a stable-intensity cyclone, let alone a hurricane going through structural changes like Katrina was during the final 12 hours before landfall. The National Hurricane Center talks about their "90% reduction rule for flight level winds versus surface winds", yet in their analysis of Hurricane Katrina, they seem to criticize their own system. They even mention that during the time of peak intensity that the reason for the dropwindsondes not finding any winds even close to the peak flight level winds and advisory winds were because they weren't being dropped in the same areas as the flight level winds were being recorded. Even better, they go on to list another reason for their downgrade as being the fact that none of the doppler radar velocities recorded or the dropwindsonde data collected near the time of landfall were near the operationally assessed intensities of 120 kts and 110 kts for each of the Gulf coast landfalls. Well, they answered their own question. They had already stated that dropwindsondes dropped in Katrina throughout her life never picked up the maximum sustained winds, so why would it be any different at the time of landfall, when it is even harder to assess the maximum sustained winds of a tropical cyclone using such precise instruments? Furthermore, the National Hurricane Center states this in their post-storm report: "Maximum 700 mb flight-level winds were still 130-135 kt east of the eye around that time and were the basis for the operationally assessed intensity of 120 kt at the Buras landfall and at 1200 UTC. NWS Slidell WSR-88D radar data confirmed the strength of these flight-level winds, but the center of the hurricane was much too distant for the radar to provide concurrent near-surface wind estimates close to the eye." So if the radar was too far away to accurately provide surface wind estimates, why use them as a reason to downgrade Katrina? It is also a fact that doppler radar estimates for surface winds are very inaccurate for such strong storms as Katrina, and after looking at numerous estimates by doppler radar for past hurricanes such as Charley, Dennis and Wilma, I have concluded that they actually might be too conservative with their wind estimates for strong hurricanes. Therefore, even if the National Hurricane Center were to use doppler radar estimates to determine the strength of tropical cyclones while approaching land or overland, there is no reason to use the precise estimates given by the radars to assess the strength of the cyclone, and instead should remember that even the most hi-tech doppler radars cannot accurately measure surface winds.

This is only part of what I have to say on the National Hurricane Center's report on Hurricane Katrina; the rest of my views and opinions can be found in my blog entry that should be finished by tomorrow.

Thank you for reading this comment and I hope everyone here has a great evening

Are you worried about global warming? Maybe you should be. Just consider that if all the Earth's glaciers were to melt, it is estimated that sea level would rise by about 250 feet.

atmosweather you give the nhc a lol you tell off atmosweather that made me mad lol you give them a lol for me
Hey David, how are you?

I am writing a very long email to the National Hurricane Center combining my views with some others' opinions about their decision to downgrade Katrina. The last time I emailed them I got a very swift response, so it shouldn't be long before I get a reply.
Anyone have a link to satellite video of some sort that shows the path of them?
Nice storms here on the west coast. The old Pinapple Express is rolling in dropping some snow but mostly rain in even the highest elevations of the sierras.

Path of what, Trouper?
hi atmosweather i am doing good i would like to few to the nhc to but i will let you do all the full that mad me mad
atmosweather i would like to say a few to the nhc to but i will let you have all the fun what where they thinking?
I emailed Dr. Masters with a question. After I get a response, I too will be making quite a lengthy email to the NHC. If we make them beat in their brains reading these, maybe something will be done.
Bad typing mistake hehe. The path of the hurricanes this year. Thanks atmos.
i like to see this up date to a cat 5 hurricane at land fall
there is no way a cat 3 can do that march and a cat 3 hurricane makeing land fall and doing more then 100B in lots come on now the A storm of 1992 was a cat 5 hurricane at landfall in fl and did this 26.4B
how do you e mail the nhc any way link on how to e mail the nhc
Yeah torn I also emailed Dr. Masters and have just written a 1400 word email to the National Hurricane Center!! I strongly suggest everyone that disagrees with the downgrade of Katrina and have evidence to back up their views to write to them. You're right; if we all send them our views, they might take notice.
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atmosweather i try that and they have not got back to me an i do not think they will
Well they got back to me very quickly (4-6 hours) when I last emailed them. I don't know why they would not reply to you. Anyway, those are the only email addresses they have and I don't know individual forecasters' email addresses, so I can't help you further. Try writing to them again.
Hey Atmos, could you post your letter here.

Also, I plugged all the new data into my scale. Katrina is still a 5 on it. No downgrade.
atmosweather did they ever get back to you last night when you e mail them i will give them 72hours to get back to me if not i will try one more time
Sorry torn, I forgot to save it and don't know if there is any way to get it back. Most of what I said was in my lengthy post about 30 mins ago, with much more added of course. Generally though, I just expanded on those points and added a lot about wind-pressure realtionships and storm surge.
hey tornadoty give what you have to the nhc and have them take a look at it
I just sent my email so I havent got a reply yet. But the last time I sent them an email they replied within a few hours
That's a good idea KRWZ. I just might.
can a cat 3 or 4 do that march when it made land fall i am thinking it was a cat 5
Yeah torn, everyone who can back up their views should definitely write to them. Something has to be done, if not for Katrina then for the next controversial storm. Not sure if they will accept anymore emails after reading my 1400 word opinion LOL!! I think I may have given all possible reasons for not downgrading Katrina!!!!
tornadoty do it do it lol
Well that's another point in itself, David. I didn't even mention that in my email because you really can't prove that a Category 3-4 Hurricane can't do that much damage.
atmosweather what did you tell them
atmosweather do you think that was cat 5 damage. and a cat 5 that made land fall
A lot of my email comes from my earlier post, and of course I added a lot to those points while also adding a lot on storm surge, wind-pressure relationships amongst many other things
atmosweather you give the nhc a lol i never want to her a hurricane being downgrade this look at all the damage that stom did and they call it a cat 3 like come on now
The damage was certainly category 5. Definitely. Now about its actual intensity at landfall. I would normally say it wasn't a category 5, but it really depends what you mean by intensity. If you mean meteorologically then it wasn't a category 5, i would say it was a category 4 145-150 at first landfall and category 4 135 at second landfall. However, if you mean by "pure strength" then it was a category 5 no question. No hurricane that did that much damage should be classified at anything below a category 5
i want that hurricane update to a cat 5 or cat 4
I am a bit more conservative than you Atmos. It was probably 135 MPH at LA landfall and 130 MPH at MS landfall. Small, but important differences fromt the NHC report.
It is an injustice if the costliest natural disaster in United States' history, the deadliest storm since 1928, and a storm that has displaced over 2 million people is rated as a category 3 storm
I can assure all of you even though that I respect each and every opinion here that Katrina was a category 4 at both landfalls. If you want me to explain I will. I am just stating my belief.
Atmos, I am not arguing with you. But please explain your reasoning so I can understand.
Yeah I know you're not arguing torn, and neither am I. I am just stating my belief and so are you. If you havent already you should watch the infrared movie of Katrina throughout its lifetime and pay attention to its structure and presentation near landfall on the Gulf coast. If you are not convinced after looking at that then I will give more explanations.

Katrina movies, click on IR next to "Hurricane Katrina Movies", it should open in Windows Media Player.
I saw it the day it made landfall and saw the burst of convection at landfall. It looked like it was strenghthening at landfall to me. I know where you are coming from. However, I think that the expansion of the pressure field dulled that effect.
The expansion of the pressure field also contributes to a much better "mixing down" process. Larger hurricanes can mix down flight level winds much better than small hurricanes. And, judging by the amount of deep convection that wrapped back around the western eyewall near BOTH landfalls, I think that Katrina attained category 4 status near landfall in LA. Since it didn't lose any of its deep convection and only weakened a little before the second landfall, I believe it was still at category 4 intensity.

By the way, I have just noticed a typo which may change your views. I meant to say 140-145, not 145-150 in my assessment that I posted.
what all go tell on the nhc or call them up
LOL David, maybe we should call them and get everyone in one place and put the phone on speaker. Then they can hear all of us complain LOL!!!!!
atmosweather whats do it call them up
That makes a ton of sense Atmos (no sarcasm).
LOL thanks torn. I agree that my estimates are very robust but I do believe I can back up everything I say, just like everyone else can back up what they say. Your estimates are pretty accruate though.
well good night you too i would like to give the nhc a lol for makeing that a cat 3 for land fall my god what will they do next? well night all
Have a great night David
Good night guys. See some of you in the morning.
Have a great night torn
atmosweather when the storm was a cat 5 at one time did they update the winds 180 or 185 or did they keep it at 175 mph
133. Inyo
it seems to me that doppler radar might be prone to error in cases of extreme wind like that of Katrina. It uses the speed of the particles (rain, etc) in wind to determine the speed, right? Well, does anyone really know how rain particles act in 140 mph gusty winds? with all the eddies, variation, turbulence, and the inertia of the raindrops themselves it seems that if anything the doppler will underestimate the winds.

also i was not trying to downplay the tragedy of Katrina at all. In my opinion, it was a human disaster as much as a natural disaster. In todays society no one should have to die in a storm you can see coming 24 hours in advance. The death toll 'could' have been much higher, in a worse case scenario, definitely. However, it could have been much lower with Katrina as well, with better systems of evacuation, more well-maintained levees, and maybe a push to get the poor (and if possible everyone else) out of these below sea level areas... not to mention better protection of the wetlands which naturally buffer storm surge. My friend who works for the park service in the area tells me that the only houses left standing in teh area he was working was the few that happened to be behind the swampland preserve.

Even if the climate never warms another degree, other hurricanes of this force WILL hit new orleans and other major cities along our coast. In my opinion, we (the US) need to do better.
I heard a few strange things during all of this that makes no sense... During its Cat 5 period seas were recorded at between 20-30 feet to the north of the eye to 50-60 feet south of the eye. How is that possible? Then seas were 20-40 feet 6 hours before landfall then it weakened more and 1 hour before they were 40-45 feet... did I miss read something or was this storm just a freak of mother nature?
Yea rmh very strange. Katrina was a freak of nature. It completed an eyewall replacement cycle lasting 24 hrs without losing a single mph in wind lol!!!
136. E
If Katrina was truly only a Cat. 3 at landfall...but yet caused phenomenal damage, what was the reason?

I know what I would say...but that's just because I'm a liberal...although were really not here to talk about politics. So, atmos, to what do you accredit the damage...because even if Katrina was a cat 4 at landfall, the most costly hurricane in U.S. history had to happen for a reason.

The bulk of the damage was caused by Katrina's world record 24-28 feet storm surge in LA and MS. Despite their being a huge amount of wind damage, the catastrophic economic losses and loss of life is attributed to the storm surge that destroyed entire towns and breached the New Orleans' levees. Now, the NHC actually try to provide a reason for that kind of surge with a mid-range Category 3 hurricane that they are trying to make us believe that Katrina was. They say that because Katrina was a massive Category 5 hurricane 12 hours before landfall it made huge ocean swells leading to 30-40 ft wave heights, and those cannot be decreased because they are already high and stick around for 24-36 hours after they generate. However, they forget that storm surge is the height of water above sea level, not the peak wave heights. That is why they measure the marks off buildings, not see how far a wave got up a building. Their reason that I just mentioned cannot be attriubted for storm surge, so they really have little explanation for Katrina's world record storm surge in a Category 3 storm. That is just one reason why the NHC are way off here and also why Katrina was the destructive force that it was.
Cat and damage don't always relate the way you think they would. Katrina was a cat 3 imo. She tore up pretty could just prior to landfall.

Surge would be my geuss as to why it was the most costly and geography. She carried a 4 to five surge with her when she made landfall and that coupled with the topography of that area led to tons of damage. And then the fact that we built a city in a fish bowl which was a disaster just waiting to happen. A slow moving cat one could realisticly cause more monetary damage then a fast moving five. or a very very large cat 1 could cause more monetary damage then a very small cat 5. So Category does not determine damage in any real way.

Great discussion though. Wish I had more time to read and comment.

Please check out my blog and help me if you can.

hey inyo i heard your from CA as well were about in ca are you ?
140. phelp
You should post your e-mail to the nhc as well. I would like to read what you have to say.
- Nick
With the types of storms we have had this year, I like the idea of a grading system that calculates pressure, windspeed and storm surge. All three components of the system can back each other up. For instance, katrina made landfall with supposed 125 mph winds and a pressure of 920. However, the storm surge was record breaking, being equally if not more destructive than the winds themselves. Thus, adding in a new catagory and taking up the 'slack of error' from the old classification system. Now, the storm surge catagory, might be been in essence 'not worthy' of making this calculation system in some peoples regards. Say if the storm would have struck a desolate place with nary a home or building, there would not be much structural damage and damage costs wouldnt be in the billions, However, storm surge is equally a factor for judging a storms sheer intensity and might, weather or not the storm strikes a densely populated area or not.
142. Inyo
Theboldman, I live in pasadena but i work in the Angeles National Forest (San Gabriel Mountians) which is why i am also occasionally talking about things like snow and summer thunderstorms LA doesn't usually get.
Folks, one small correction, the world record is 42 feet, by some Australian cyclone about 100 years ago.
And Trouper, look at my blog.
atmosweather wrote:

"The damage was certainly category 5. Definitely. Now about its actual intensity at landfall. I would normally say it wasn't a category 5, but it really depends what you mean by intensity. If you mean meteorologically then it wasn't a category 5, i would say it was a category 4 145-150 at first landfall and category 4 135 at second landfall. However, if you mean by "pure strength" then it was a category 5 no question. No hurricane that did that much damage should be classified at anything below a category 5"

I'm in agreement with you on the landfall strength...around 145 at first landfall in LA, and 135 at second landfall in MS. Katrina made landfall as a large and very powerful Cat 4 storm, carrying a record-breaking Cat 5 surge (28-30 feet) into the Gulf Coast. The NHCs downgrading of such an historic storm would be unprecedented, AFAIK. We have cases of storms being bumped up in strength after further analysis (Andrew, Charley), but not the other way around, at least not to the extent that Katrina's landfall strength is being "modified" by the NHC.

Katrina was a STRONG Category 4 at landfall...that is what the evidence shows, and that is how the NHC should write the final report. Anything less would ignore reality.
A couple questions about this post.. not directly hurricane related:

1. could you post your references, please. I've been trying to find decent explanations/theories for the atlantic multidecadal mode for some time, and have been unimpressed.

2. I am a little confused by your explanation. The gulf stream is a result of western intensification (aka, western boundary current). It is almost entirely wind driven; basically the trade winds blow the water south and west over the tropical Atlantic and the Coriolis force, conservation of momentum, and the existence of the continent (stopping the water from going further west) all combine to make a very strong, narrow current, which we call the gulf stream. There are similar currents on all the major western boundaries. The thermohaline circulation, as its name tries to imply, is driven by density differences of sea-water that arise from differences in temperature and salinity. Thus, the two currents are fundamentally different phenomena (dynamics versus thermodynamics). The blog entry seems to equate them and their variations, but that doesn't seem right. My guess is that "gulf stream" should not have been mentioned at all, as the rest of the sentence seems to implicate the THC. Is this the right interpretation, or am I missing something?