Guest Post by Willis Eschenbach
When is a hurricane not a hurricane? Well, when it doesn’t blow 64 knots (33 m/sec, 74 mph), because then it’s only a tropical storm. Inspired by a post over at the Cliff Mass Weather Blog, I’ve been trying to find a single report of sustained hurricane force winds anywhere along Irene’s path at or near landfall … no joy. I knew exaggeration was the order of the day for some folks in the climate debate, but I hadn’t realized that the illness had infected the Weather Service itself.
Figure 1. The path of Tropical Storm Irene over the mainland of the US. Symbols with a yellow center to the black storm symbol indicate a (claimed) hurricane. SOURCE ibiseye
We were fortunate in that we have very good records of the wind speed when Irene made landfall. It went almost directly over the wind recording station at Cape Lookout, at the bottom of Figure 2.
Figure 2. A closeup of Irene’s landfall. There are four wind recording stations in the area, at Beaufort (below the “70” marker at lower left), at Cape Lookout (bottom left) and at Cape Hatteras (upper right). The Onslow Buoy is located offshore, southwest of Cape Lookout.
The wind record at Cape Lookout is quite interesting, as the eye of the hurricane passed right over the anemometer there. Figure 3 shows the wind dropping as the eye went over, coincident with the deep plunge of the barometric pressure to 950 hPa.
Figure 3. TS Irene wind (light blue) and barometric pressure (violet) at Cape Lookout before, during, and after landfall. Green line at the top shows the minimum wind speed for a storm to be classified as a hurricane (64 knots).
Figure 3 shows the classic pattern of a hurricane passing directly overhead. The “eye” of the hurricane has almost no wind, and is at the center of the low pressure area. You can also see the “calm before the storm. But what you can’t see is any trace of hurricane force winds.
Not finding hurricane force winds at the eye, I looked at the other nearby stations as well. The weather station at Cape Hatteras is in the “dangerous semicircle”, the right hand side of the storm track (Fig. 2) where the speed of the storm is added to the speed of the winds circulating around the eye. Beaufort, on the other hand, is in the safer half of the storm, where the speed of the storm is subtracted from the circulating speed of the winds. The Onslow Buoy is also in the safer semicircle, on the left of the storm track in Figure 2. Figure 4 shows those records.
Figure 4. Winds at TS Irene landfall for Cape Lookout, Beaufort, Onslow Offshore Buoy, and Cape Hatteras.
As you can see, although Irene definitely qualifies as a solid tropical storm (winds greater than 35 knots), it does not reach or even really approach the 64-knot threshold for hurricanes. Other than at the eye itself, the winds did not exceed 50 knots, much less reach 64 knots.
After crossing over the land near Cape Hatteras, Irene headed back out to sea again. I thought perhaps it might have picked up steam when it went out over the ocean again. It made a second landfall in Atlantic City and went along the coast to New York.
Figure 5. Second landfall for Irene.The nearest stations to Irene’s track are Costeau (near Mystic Island above Atlantic City), NY Harbor Buoy (outside the mouth of the harbor, in the dangerous semicircle), Sandy Hook (hook shaped peninsula just above Long Branch and central hurricane symbol) and Kings Point (near New Rochelle above New York City). Note that the storm is claimed to be a hurricane until it gets well into New York State.
It appears from an examination of the station data shown below in Figure 6 that it did not pick up strength over the water. By the time Irene reached land a second time, it barely qualified as a tropical storm, much less a hurricane.
Figure 6. Wind speed from Tropical Storm Irene as it made the second landfall.
So, despite looking at Irene before, during, and after both landfalls, there is no hint of a hurricane anywhere. By the time it got to New York the eye of the storm had dissipated, what was left were huge bands of rain clouds.
Is there a moral in this story? Well, I can understand people taking extra precautions, better safe than sorry is a good rule. And I certainly imagine that when the Weather Service re-examines the records, the error will be corrected.
But that doesn’t help in making the decisions. As soon as Irene hit land, it should have been downgraded immediately to a tropical storm. That’s what it was, not a hurricane making landfall but a tropical storm. As far as I can tell, we still haven’t had a hurricane make landfall during Obama’s presidency, a historical oddity.
Individuals and city mayors and the people in charge of the emergency response can call for any level of reaction to storm threats. They may decide an exaggerated response is appropriate.
But they need accurate information to do that, not exaggerated claims. They need the actual facts, the best estimates with no exaggeration on either the high or low side.
In this case, it appears that people got so wrapped up in the question of the winds, and the fear of the winds, that they overlooked what actually made Irene unusual. This was not the wind speed, but the size of the storm. Combined with Irene’s generally slow movement over the ground, Irene’s huge dimensions meant that any given area would get rained on for a really, really long time.
And in turn that meant that the cities and towns along the coast, the ones receiving all of the attention from the fear of high winds and attendant storm surges, weren’t the towns in danger. Unlike the coastal cities, the vast expanses inland were not able to have the rainwater just flow back into the ocean. Inland, the water piled up and overflowed the banks.
And so, because of the overestimation of the wind speeds, our attention was diverted from the real threat. Because of the claimed hurricane-force winds, a storm surge up to eight feet was predicted in New York Harbor. But in the event, the storm surge was barely three feet, a non-event … and meanwhile, New England was getting badly flooded.
So the moral to me is, honesty is the best policy for a National Weather Service. Don’t exaggerate the possible effects to be on the “safe side”, don’t minimize the possible effects. Just give us the best information you have, and let us make up our own minds. As Sergeant Friday used to say … “Just the facts, ma’am” …
w.
NOTE: All wind data is from the NOAA National Buoy Data Center http://www.ndbc.noaa.gov/.
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The conspiracy? The prevailing govt and the media want us citizens to believe in manmade global warming. Why? So they can have more control over us. The marxists figured out a while ago that the environment is a strong playing card. Some scientists are excited to play along. AGW was suspected 1000 years ago, but they are still trying to detect it. It has not been proven. Hurricanes are not drastically increasing in strength and frequency according to prediction. The AGW proponents have egg on their collective (no pun intended) face.
But now that all of Storm Irene’s energy can be declared a ‘hurricane,’ its cyclonic activity can be added to the cumulative sum for this season. This is necessary, since this year otherwise would be another disappintment just like last year.
I noted to friends as it happened that the storm might have been a hurricane, technically, as it crossed into NC, but if it was a hurricane, it was not for very long. I hear exclamations of 90mph winds at landfall, but saw no evidence. I knew the fix was in.
I do not know about “post-season analysis.” A Congressional Investigation might be needed, too. The feeding of the frenzy could not be done by one person.
When I saw that Irene was heading for NYC I decided to tune out. Knowing how the American Media works (everything seems to be centered around NYC/East Coast) I knew that the coverage would be the “OMG we’re all going to die!” style, and so it was.
I hate to see otherwise sane people, some of whom are widely respected, getting sucked into defending NHC on this. If there is some special category of hurricane that says “it’s a hurricane here, but the winds are over there” hurricane, then NHC needs to create a category for it. I’ve been in a Cat 1 on the east coast, and it wasn’t just gusts but a steady building wind that was blowing the rain sideway for a few hours either side of a dramatic wind shift. The sound of transformers blowing out was replaced over time by the sound of large limbs snapping and trees falling. When Georgetown SC was demolished by Hugo, it wasn’t due to winds in a patch somewhere east of the (actual) eye of the storm.
If the NHC says the thing has 85 knot sustained winds, it had better actually have winds of that intensity, otherwise the winds are …not …of …that …intensity! And if not at the presumptive eye, then they really should qualify their claims up front. In this case, were talking about the instance of landfall, when folk (as Obama would say), started wondering why there were NO actual reports of hurricane winds — even from NOAA. Even at sea east and northeast of the storm, according to buoy data. Despite all evidence, the bureaucrats insisted on maintaining their fiction until the bitter end. What confidence was thus inspired…
Meanwhile, lots of rain and low pressure do not make it a hurricane.
Chip Knappenberger-I think that the fact that the observation was made at 19.4 m could potentially mean it will not play that role (the other wind analysis very well could). Should not the wind speed be expected to increase with height? Granted it is a small height difference, but I would still like to see someone give a “surface estimate” for 10 m wind speed based on that.
BTW, someone asked about the 2 minute versus one minute distinction:
http://www.aoml.noaa.gov/hrd/tcfaq/D4.html
Apparently the change was to two minutes as a result of ASOS.
Well off the mark here I’m afraid. It’ll contribute to the ACE index by virtue of being a tropical cyclone, regardless of intensity. You seem to have overlooked that it was a hurricane for a good five days, no matter what its intensity at NC landfall may have been.
Hi Paul,
I guess the difficulty the NHC have been grappling with is that there isn’t such a hard and fast link between maximum surface wind speed, minimum central pressure, maximum storm surge, maximum wind field/radius, maximum expected rainfall and expected structural damage, that can be simply categorised in a scale.
Sure, it’s the effects of the hurricane that matter, rather than its raw statistics, but in the absence of simple and direct relationships between the different facets it makes more sense to categorise by the most obvious facet, wind speed, and give details individual to that system for the other facets.
A good case could be made for the driving facet to be minimum central pressure, as it’s the easiest to measure, but by itself it isn’t indicative of the likelihood of damaging effects, as the pressure gradient is what determines wind speed.
alexwade said: “I can tell you from experience that this was a hurricane. Barely a hurricane, but one nonetheless. The wind speed near the surface can be different than the wind speed higher up.” You must be ten meters tall to have been able to tell this.
When (historically) did this become a 1-minute average for hurricane strength?
It looks like with the advent of ASOS. The following text is from this URL:
http://www.aoml.noaa.gov/hrd/tcfaq/D4.html
“Since the inauguration of the Automatic Surface Observation System (ASOS) the National Weather Service has adopted a two minute average standard for its sustained wind definition. This is because the ASOS stations average and report their wind data over a two minute period. There is no conversion factor to change a two minute average wind into a one minute average wind, and it is pointless to try to estimate the highest one minute wind over a two minute period, as they are essentially the same.”
Sorry about my previous post. What I meant to say is that it looks like wind speed became a 2-minute average with the advent of ASOS. Otherwise, I believe that wind speed has always been a 1-minute average in the U.S.
Willis, the main contribution H*WIND makes is the “snapshots” of the data incorporated into the “gridding” routine. H*WIND combines the in-situ data + the US Air Force recon data. Many of the intensity estimates for flown storms absolutely rely on a combination of Dvorak satellite intensity estimates from visible and IR imagery as well as SMFR recon data.
It is this last piece of information that likely kept Irene as a hurricane in the forecasters’ analysis. My final appraisal suggests that Irene should have been downgraded about 6-hours earlier than it was. An email thread as developed elsewhere, and I posted this:
H*WIND provides snapshot maps of the observations that are included in each analysis window – an example is attached. Essentially, it coalesces all available in-situ and recon info into one package, which I find pretty handy even with the (un)known uncertainties in the gridding routines.
Even if your contention that H*WIND is unreliable and widely in error is correct, the H*WIND analysis still helps to make your case for downgrading Irene to a tropical storm no later than 00z 08/28 – with the benefit of hindsight.
At 1855z on 08/27, maximum observed surface winds of 71 knots were observed by SFMR (Air Force).
At 2106z on 08/27, the maximum observed surface wind was 63 knots 12 nm NE of the center (CMAN)
At 0102z on 08/28, SMFR observed 62 knots
If you look at each additional HWIND map, you will find that the maximum observed surface winds did not exceed 58 knots again, which were measured largely by SMFR.
Acknowledging that we cannot sample the entire storm and our measurements have uncertainty, the 08/28 06z intensity of 65 knots does not seem outlandish at all except that it represents the hurricane threshold, clearly your main point. I suspect in the post-season analysis, this will indeed be dropped to 60-knots, and Irene’s lifetime as a hurricane will be reduced by 6-hours.
Couple thoughts: how does the public respond to warnings of a “strong tropical storm” vs. a “weak hurricane”?
And, I think if we could predict earthquakes 12-24 hours in advance (with our Irene experience with the hyperactive media), then communicating that threat would be quite a challenge.
Main H*WIND page: http://www.aoml.noaa.gov/hrd/Storm_pages/irene2011/wind.html
snapshot link: ftp://ftp.aoml.noaa.gov/hrd/pub/hwind/2011/AL092011/0828/0130/AL092011_0828_0130_dataCoverage02.png
Irene was misrepresented on two fronts – the WS trumped it up and the blogosphere downplayed it. Very few called it what it was – a dangerous storm, worthy of much precaution, that was capable of sudden death, property loss and damage, and flooding. It was also capable of strumming up a seiche in Chesapeake Bay but that failed to materialize.
The lingering problem is not what resulted from the testosterone surrounding Irene – the problem is how Katia is perceived, and the one after, and so on. All the reshashing that continues around Irene seems to ignore the death toll, and the fact that people are without power and all the human necessities that provides.
With a lot of summer left, next will come the mosquitoes adding additional misery and disease to the now windowless homes of the Atlantic coast.
When the public loses faith in the official statements and either ignores or heeds the equally shabby blogosphere view of things the likelihood of greater disaster increases. It is clear from watching eye witness testimony that many people in harm’s way have no idea what a storm surge is. Many equate it to large waves gorgeously portrayed on Hawaii’s north shore – awesome entertainment between beers. In fact it is more like a dam breaking. Somewhere between the overshooting and underplaying is the truth and hopefully that is what will be reported next time. It does not have to be a hurricane class storm to be a killer – according one one noisy blog it required only 33 mph winds to do all that damage. Anyone believe that happened?
Mike Maxwell says:
September 1, 2011 at 6:56 pm
alexwade said: “I can tell you from experience that this was a hurricane. Barely a hurricane, but one nonetheless. The wind speed near the surface can be different than the wind speed higher up.” You must be ten meters tall to have been able to tell this.
Or have access to a flight or two of stairs and a window…
About trees going down in tropical storms or hurricanes (=cyclones/ typhoons):
If they are have barely broken branches and the roots came out when it fell it over, it is because of the rainfall that saturated the soil first. Any wind can then tip a weak/ exposed tree over.
If there are many broken branches or even roots or trunks on a fairly dry ground then blame hurricane winds.
I’ve see both and they are distinctly different.
By historical convention this was a tropical storm. It’s just that people wanted it to be a hurricane. The emergency response levels are different. Even one wind reading at CAT 1 levels wouldn’t mean it was a CAT 1 hurricane. Storms are dangerous at any level. Accurate forecasting is the desired outcome.
In the 70’s, there was a wind scale and all wind readings were taken a few feet off the ground. That is what went into the records. Hurricanes had the eye, and the spiral cloud bands, winds. Maybe at some point it becomes semantics, but convention still points to tropical storm.
Wind readings at higher off the surface elevations were by http://www.merriam-webster.com/dictionary/rawinsonde
Radar should also have picked up any tornadoes that were about.
If people want to count water damage, large power outages, low pressure as hurricane indicators. Well that calls for a conference.
Willis…I have a ton of respect for you when it comes to logical deduction on the climate issue, but you’re showing your basic lack of knowledge about weather reporting here. If Irene was not a hurricane over eastern North Carolina…then neither was almost any other storm that ever cross those outer banks. The fact is that we always ESTIMATED the wind in the bad old days and we called a storm a hurricane when it had what we ESTIMATED to be sustained winds over that 74 mph threshold. We had no way until very recently of measuring a “sustained wind” during a storm…our instruments would break and even if they didn’t, we would have to sort of…eyeball it as to what wind force was being sustained over at least three straight minutes. What IS a sustained wind anyway?
The bottom line is that Irene did have surface winds well over that 74 mph threshold according to dropsounde data from hurricane hunter aircraft all the way to very near her landfall in North Carolina…and that those winds had trouble making it all the way down to the surface because of frictional affects…but this is probably true of MOST category 1 and even category 2 hurricanes (as measured over the ocean). You obviously live nowhere near the impacted areas. I actually LIVE on Long Island and this was a hurricane here. Period. The amount of wind damage we suffered here was only matched in recent memory by Hurricane Gloria…which also failed to produce many confirmed reports of sustained winds exceeding hurricane force.
This is all silly…why we are so “precious” about what to call something…if it’s 63 knots…well that’s not a hurricane…but by god…3 more knots and now you’re talking!…is beyond me. I’m tired of reading this stuff about Irene being overhyped. You tell that to the people drowning in Vermont and New Jersey or the people still without power in Central Long Island.
Thanks Willis. Lucid prose and analysis as per usual. The problem as I see it is that a whole bunch of east coasters just got ‘trained’ to what a hurricane ‘is’.
Only …. it WASN’T a hurricane. If its a Cat 3 – the wind damage and surge can be amazing… TS and TD can carry a lot of rain and cause flooding – but what gets the coverage is the wind field.
They completely overhyped it. They should approach these things as ‘teachable moments’.
Keith says:
September 1, 2011 at 3:54 pm
That’s why I was glad to have the data from Cape Hatteras, in the eastern portion of the track, because that’s the semicircle with the highest winds. It was within 40 miles of the track and didn’t see hurricane force winds.
As to whether it was a hurricane at the time it made landfall, seems to me that the definition of that would be that a land station actually recorded hurricane force winds … no?
w.
Interesting post, Willis, and points taken.
Irene was a hybrid storm when she reached the mainland USA. When her center passed near me (I was out in it…oops) it was like a really intense mid-latitude cyclone or nor’easter and there was definitely no suffocating tropical air in the core. Actually, it was rather cool.
The classifications of tropical storm / hurricane / and the saffir-simpson system certainly have their limits…especially in the temperate latitudes.
Joe Bastardi proposes a power scale and that is more intuitive and less plastic.
Also the Integrated Kinetic Energy scale or, ironically, the “IKE” which did a good job of warning the populated areas in advance of the extremely destructive, but only “category 2” Hurricane Ike in 2008. Measuring the total energy output in terrajoules, seems like a good idea…and it no doubt saved many lives on the Bolivar Peninsula in Texas.
Even though Irene’s winds were not as intense as they could have been, and you rightly so point out the lack of storm surge at Battery Park (even though I think the mb pressure was within the range of a category 2 as well), even so…$7.2 Billion dollars and about 45 deaths out…Irene was no cakewalk.
Points taken however. Its just when a potential disaster could *could* affect the most densely populated region on in the United States with hundreds of high rises within eyeshot of the Atlantic, it is understandable why such precautions are taken.
But then weighing the risk from the Nanny State Government…and reality…is another thing. There is always the “cry wolf” danger, too.
We certainly need to evolve our “classifications” of destructive storms…based upon their potential to destroy and not on some rigid legalistic definition, so points taken and interesting post!
Chris
Norfolk, VA, USA
dp says:
September 1, 2011 at 7:08 pm
Irene was misrepresented on two fronts – the WS trumped it up and the blogosphere downplayed it. Very few called it what it was – a dangerous storm, worthy of much precaution, that was capable of sudden death, property loss and damage, and flooding. It was also capable of strumming up a seiche in Chesapeake Bay but that failed to materialize.
The lingering problem is not what resulted from the testosterone surrounding Irene – the problem is how Katia is perceived, and the one after, and so on. All the reshashing that continues around Irene seems to ignore the death toll, and the fact that people are without power and all the human necessities that provides.
==============================
Extremely well said. Entire post.
Chris
Norfolk, VA, USA
Chip Knappenberger says:
September 1, 2011 at 4:19 pm
Wind speed goes up rapidly with height, so it would have to be corrected.
More to the point, you are discussing gusts, not sustained winds. Since the sustained winds were never more than 58 knots, why would I be “hard-pressed” to say it was not a hurricane?
The NHC is free to call it what it will. Given that they called it a hurricane when it hit New Jersey/New York, at a time when it barely was a tropical storm … I’m not sure I how they choose what to call it.
I’m simply pointing out that according to their official definition, there is (so far) no evidence that it was a hurricane at landfall or at any time afterwards.
w.
timetochooseagain says:
September 1, 2011 at 6:35 pm
Outstanding, many thanks. They also say
So the 2-minute data we have is valid for the “sustained winds”.
w.
Perhaps they are using the humidex wave trick. When you factor in all the media activity, did it feel like a hurricane?
PaulID says:
September 1, 2011 at 5:24 pm
“The point here is I believe that the damage that was done was by a TROPICAL STORM they need to let people know that so they can know to get out if a real hurricane shows up.”
Right. If you get hit by a Cat1 then you will lose all trees that are 70 years old. Cat 1 and Tropical Storm are entirely different critters. If a Cat 1 is bearing down on you and you can leave town then you must leave town. Services will not be restored within a week.
Willis Eschenbach says:
September 1, 2011 at 8:10 pm
“As to whether it was a hurricane at the time it made landfall, seems to me that the definition of that would be that a land station actually recorded hurricane force winds … no?”
Ah, Willis, there you go again, demanding actual records and such. Don’t you know that a hurricane is what the “Consensus of Federal Bureaucrats” deems to be a hurricane. If you are going to go all factual on us, the Consensus will lose the joy of being the Consensus, the joy of theorizing, and the joy of looking down on the Rednecks who believe that land stations cannot be overruled by theory.