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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Willis, with the benefit of hindsight, the NHC should have downgraded Irene for that 28/0900z advisory. From the HWIND analysis, which including data that comes in much too late for real-time processing, the last time a hurricane force surface wind could legitimately be claimed is probably 27/2230z when it was crossing the VA border.
ftp://ftp.aoml.noaa.gov/hrd/pub/hwind/2011/AL092011/0827/2230/AL092011_0827_2230_contour04.png
However, there was a finite chance that convection would re-fire as Irene moved over the somewhat warmer waters again. Mixing down the hurricane force winds in bursts of convection likely did happen, but those were not (and are not) easy to sample.
Thus, it should have been a 60-knot tropical storm for the 06z 08/28 advisory and I suspect the post-season analysis will show that.
The lesson to be learned is that large Tropical Storms are dangerous and costly.
Whether or not Irene was overhyped, the greatest sin was the quick accusations of “overhyped”, and “over-reactions” made by the MSM reporters.
Fortunately, Gov. Christie set many straight when he said in effect, “This isn’t about the wind. It is about the rain. Rivers are flooding. We have 3 dams that are at historic highs. One is 1.5 feet above record and I’ve orderd the evacuation of the town below it.”
Tropical Storm Allison (2001 Houston) taught me that a TS is nothing to pooh-pooh. Wind damage is over quickly and often limited to tornados within the wind field. Flooding on the other hand is where people most likely lose property and lives.
So the debate should not be whether Irene was a Hurricane or TS. The debate should be why fools think Tropical Storms are not worth evacuation, shutting down transporations systems, and other sensible precautions agains flooding.
Joe Bastardi says:
September 1, 2011 at 11:02 am
Sadly, this whole argument is probably finding its root with the maliciousness of the AGW crowd that wants to pump weather events up to emphasize global warming. And I understand our need to fight back.
==========================================================================
I agree with the above quote by you without any reservation.
You have my respect. I would normally not doubt any opinions that you may present. However, where are the wind records verifying what has been reported. Those records should be widespread. In real science and reporting on somthing as serious as a hurricane approaching landfall, report the facts!
To begin after the fact on changing the rules of classifyng hurricanes now would be in effect moving the goal posts or redefining the rules as best suites ones objectives. Does “redefine what peer review is” ring a bell. In weather/climate issues there has been too much of that already.
If you are caught playing politics or ‘Nanny State’ you need to get a job in one of those professions. Head, meet chopping block or tell the truth.
Put nicely above: “Just the facts, Ma’am. Nothing but the facts.”
JR says:
September 1, 2011 at 12:45 pm
My bad. The land stations are all two minute averages, and the buoys are 8 minute averages. From the definitions:
and “gusts” are
w.
Got here via link on ArsTechnica, parents have home near Morehead City, NC so this was interesting…
When I look at the Cape Lookout buoy data for 8/27, it looks like they showed gusts above 34 m/s (>66knots) from 7AM to 9AM, followed by the eye passing over the site. Data from http://www.ndbc.noaa.gov/data/realtime2/CLKN7.txt
This would be consistent with a Cat1 landfall, not a TS.
Thank you, thank you, thank you!
I have been following hurricanes since Dona went over my head in Sanford, Florida in 1960 and we were out of school for over two weeks. I have seen weak canes and strong ones like the recent Hurricane Charley; and I have seen tropical storms. Why have a hurricane definition and a hurricane scale if the government agencies are just going to make numbers up for the hell of it?
I watched the weather stations the whole life of Irene and never saw hurricane strength. Now either NOAA is incompetent or all the weather stations are broken. There seems to be no other possible choice.
,blockquote>Willis Eschenbach says:
September 1, 2011 at 12:30 pm
Keith says:
September 1, 2011 at 11:44 am
From satellite presentation, and from the location of wind reports, might Irene have been a subtropical storm of hurricane strength at landfall?
No, because the data to date clearly shows that Irene did not have “hurricane strength at landfall”.
w.
Hi Willis,
Thanks for responding. As others have said, I think it’s premature to say that no it wasn’t of hurricane strength. Preliminary/incomplete data can’t clearly show a negative, Additionally, if the Cape Lookout wind speed peaked at around 58kt (looks about that) for an 8-minute period, the rule of thumb difference for a 1-minute period would make it 66kt, just about hurricane force.
I always appreciate your forensic analysis and the way you present it. I think maybe you’ve jumped the gun a little in calling this one though.
Either way, it’s a marginal call. What it certainly wasn’t was a tempest worthy of making TV reporters hide behind shelters on Long Beach and stagger sideways, while regular folk strolled or cycled calmly along the promenade behind them 🙂
Ryan Maue says:
September 1, 2011 at 1:28 pm
Thanks, Ryan. As always, more questions. First, your link to the wind speed contours is great, thanks.
Second, what is the “HWIND analysis”? Is that what your link is to?
Third, do you have a link to the NHC advisory you quoted above?
Finally … if the HWIND analysis is too late for real-time processing, what data were they looking at when they claimed it was still a hurricane when it was just off of Atlantic City?
There’s an interesting comparison of the forecasts and the HWIND data here.
w.
Here in North Texas, we are quite familiar with dangerous thunderstorms. These cyclonic storms produce sustained winds in the range Willis discussed. They also produce the kind of wind damage that Joe wrote about. I would suspect there were outflow straight line winds that caused the major wind damage. In the Dallas area, it is not a rare occurrence to have these t-storms produce outflow winds exceeding 90–110 mph. These are not long lasting, but the mess they leave behind can take a while to clean up. As with Irene, the major disruption is due to flooding, not the winds.
Stephen Rasey says:
September 1, 2011 at 1:29 pm
Stephen, you miss the point. We can’t evacuate all possible areas and shut down all possible transportation systems for every tropical storm. We depend on the weather service to let us know how strong the storm is going to be, so that we can match our response to the threat.
In this case, the strength of the winds (and thus the resulting storm surge) was way over-estimated, leading to costly un-necessary shutdowns and evacuations.
w.
The U.S. Army Field Research Facility recorded a 1 minute sustained wind speed of 32.6 m/s at 1600 EST on Aug 27 from their 19.4m anemometer locatated at the end of the pier in Duck, NC. Not quite 64kts, but pretty darn close.
Data: http://www.frf.usace.army.mil/cgi-bin/metlist.pl?gage=undefined&syear=2011&smonth=8&eyear=2011&emonth=9&tzone=EST
Data description: http://www.frf.usace.army.mil/weather/aboutweather.html
Seems pretty fortuitous if this specific location were to be at the exact point of max winds.
-Chip Knappenberger
Willis
An interesting exercise would be to look at another recent landfall hurricane, one in the last 8 years for example, and compare the wind records on the ground at landfall to the data shown by the hurricane centre. If it is truly an altitude issue, and they must estimate it at 10 meters cause they are not actually measuring it, then past hurricanes should show the same difference between recorded ground level data and the reported windspeeds. If the gap doesn’t exist in past examples, then there is a real problem somewhere.
I’ve tried this exercise a number of times even on upper Category storms. Inevitably the ground measurements always look lower to me than what I would have expected. I think there is a systemic cause, maybe measurement devices are non linear above a certain wind speed.
Tom in Florida: “In the case of Irene, potential damage was estimated to be that of a Cat 1 hurricane and it certainly was without regard to the recorded wind.
End of story.”
It isn’t the end of any story. We were constantly told that Irene had maximum sustained winds of 80mph and would hit as a “strong” cat one. I want to know on what bases was that claim made. Some people seem to think that it is ok to panic people unnecessarily as long as the intentions are good. But I disagree closing the New York City transit system for no reason cost business and people $billions and may have cost people their life.
On the other hand the failure of The National Hurricane center and the News Media to adequately warn Vermont of flooding was almost malpractice.
Willis, Ryan, others: thanks for a good thread.
Joe Bastardi: Why do you continue to say that Irene was like Ike? In my estimation Irene was very similar to Gloria and was for quite some time. It went slightly more West and had more flooding in Vermont, but otherwise I think they were very similar.
I find it interesting how this story has fallen prey to the “hype” and “conspiracy” theorists that love to look at very specific facts that support their line of thought but miss the bigger story. Yes NYC was largely spared by the hurricane, but I live 30 miles due west of the city in NJ and we are still struggling to recover – power is still out through most of the area, some businesses have not been able to open due to structural damage to the buildings, and in our case, the start of school has been pushed back 1 week so engineers can assess the damage to the school buildings (which are still without power). The damage was caused by a combination of flooding and wind toppling trees and debris breaking windows that lead you to believe the winds in this area were quite severe. However, the NJ beaches and NYC made it through the storm with relatively minor damage compared to the damage inland.
To echo what other’s have said – Willis is assuming the Surface winds=Storm winds. A tropical storm is measured by the strength of winds at altitude, not on the surface.
Finally, I also echo other comments but in reverse – how could the forecasts be so wrong? I’ve been living in this area for 50+ years and never seen the amount of damage we experienced last weekend with Irene. JCP&L is forecasting complete restoration of power by September 6th – 10 days after the storm hit!
Not sure what the point of this post is. Even the NHC qualified its status with regard to category:
The 5AM Aug 28 bulletin (in part):
SUMMARY OF 500 AM EDT…0900 UTC…INFORMATION
———————————————-
LOCATION…39.2N 74.5W
ABOUT 15 MI…25 KM SSE OF ATLANTIC CITY NEW JERSEY
ABOUT 115 MI…190 KM SSW OF NEW YORK CITY
MAXIMUM SUSTAINED WINDS…75 MPH…120 KM/H
PRESENT MOVEMENT…NNE OR 20 DEGREES AT 18 MPH…30 KM/H
MINIMUM CENTRAL PRESSURE…958 MB…28.29 INCHES
DISCUSSION AND 48-HOUR OUTLOOK
——————————
AT 500 AM EDT…0900 UTC…THE CENTER OF HURRICANE IRENE WAS LOCATED
BY AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT AND NOAA DOPPLER
RADAR NEAR LATITUDE 39.2 NORTH…LONGITUDE 74.5 WEST. IRENE IS
MOVING TOWARD THE NORTH-NORTHEAST NEAR 18 MPH…30 KM/H…AND THIS
MOTION ACCOMPANIED BY A GRADUAL INCREASE IN FORWARD SPEED IS
EXPECTED DURING THE NEXT DAY OR SO. ON THE FORECAST TRACK…THE
CENTER OF IRENE WILL MOVE NEAR OR OVER THE COAST OF NEW JERSEY AND
OVER WESTERN LONG ISLAND THIS MORNING…AND MOVE INLAND OVER
SOUTHERN NEW ENGLAND BY THIS AFTERNOON. IRENE IS FORECAST TO MOVE
INTO EASTERN CANADA TONIGHT.
DATA FROM THE HURRICANE HUNTER AIRCRAFT INDICATE THAT MAXIMUM
SUSTAINED WINDS HAVE DECREASED TO NEAR 75 MPH…120 KM/H…WITH
HIGHER GUSTS. IRENE IS A CATEGORY ONE HURRICANE ON THE
SAFFIR-SIMPSON SCALE. LITTLE CHANCE IN STRENGTH IS EXPECTED BEFORE
IRENE MOVES INLAND LATER TODAY.
—
And from the same Discussion issued at the same time:
HURRICANE IRENE DISCUSSION NUMBER 32
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092011
500 AM EDT SUN AUG 28 2011
SATELLITE AND RADAR IMAGERY SHOW THAT DRY AIR IS NOW WRAPPING INTO
MUCH OF THE SOUTHERN SEMICIRCLE OF IRENE…AND THE CYCLONE IS
SLOWLY BEGINNING TO FILL AS MEASUREMENTS FROM THE AIR FORCE RESERVE
HURRICANE HUNTER AIRCRAFT SHOW THAT THE CENTRAL PRESSURE IS UP TO
958 MB. BASED ON DROPSONDE AND SFMR DATA SHOWING THAT SURFACE
WINDS HAVE CONTINUED TO SLOWLY WEAKEN…THE INITIAL INTENSITY IS
LOWERED TO 65 KT FOR THIS ADVISORY. DESPITE THE GRADUAL WEAKENING
OF THE CYCLONE…THE OUTER WIND FIELD CONTINUES TO EXPAND…WITH
34-KT WINDS OCCURRING FROM NEW YORK CITY SOUTHWARD TO NORTHEASTERN
NORTH CAROLINA. IRENE IS EXPECTED TO REMAIN NEAR HURRICANE
STRENGTH UNTIL IT MOVES INTO SOUTHERN NEW ENGLAND LATER TODAY…
AND IT WILL ONLY TAKE MODEST CONVECTION TO BRING DOWN STRONGER WINDS
ALOFT TO THE SURFACE AS SUSTAINED HURRICANE-FORCE WINDS OR GUSTS.
SLOW WEAKENING IS EXPECTED AFTER LANDFALL AS IRENE BECOMES A
POST-TROPICAL CYCLONE IN ABOUT 24 HOURS..
…
Collapsing was obviously occuring, but at the time, it was not clear just at point the huricane was at. So what is the NHC to do – tell everybody its a tropical storm, and have folks lower their guard and perhaps get caught short, or hold the cat 1 desdignation a little longer until the outcome was more clear, and perhaps protecting a few lives. You’ll be hard pressed to tell the people in Vermont it wasan’t a hurricane, even if it wasn’t by the time it got there. Much ado about nothing
The models had it to a cat 2 or 3 until it was right up to the coast, and as a cat 1 all they way to New England for the first early contacts.
….
The problem I see is up the east coast there is now a population of people who think a hurricane is a breeze (pun intended).
@Joe Kirklin Bastardi: I Second
Larry Miller says: September 1, 2011 at 12:38 pm
Larry put it best. The problem with trees was waterlogged ground with huge trees. We haven’t had a significant east cost wind storm in many years. So now we’re getting the damage all at once. I’ve been through a number of hurricanes, and, what we got in Baltimore was nowhere close. Loose tree limbs didn’t even get blown down in norther DE nor did they really lose power. Up in PA, I hear it’s a different story because of all the rain they received in August.
I support Willis in calling BS on the “hurricane” wind speeds.
Hi Willis,
To save Dr Maue some time (his is worth more than mine, that’s for sure), here’s the link to the NHC discussion he posted earlier from 08/28 5am:
http://www.nhc.noaa.gov/archive/2011/al09/al092011.discus.032.shtml?
and here’s a piece about HWIND:
http://www.aoml.noaa.gov/hrd/data_sub/wind.html
🙂
I am a bit late to this discussion, but I really want to thank you Willis, for an excellent article. You have captured the essential points very well.
Jeremy says:
September 1, 2011 at 1:27 pm
Dunno, that’s what I’m trying to find out, why they claimed hurricane force winds when there is no record of them either at the buoys or on the land …
w.
Protyase says:
September 1, 2011 at 1:37 pm
Gusts, whether above or below 34 m/s, are meaningless in deciding whether to call it a hurricane. I show the winds for the station you reference in Figure 4, it’s Cape Lookout, nothing over 64 knots. It’s also not a buoy, it is a land station,
w.
Likewise, but with the major ‘canes it’s often the case that the wind gauges are broken before they are able to record the strongest winds. That probably won’t be the issue with Irene, or else maybe some of those TV reporters weren’t quite as flaky as we thought…