Discussion of Intense Tropical Cyclones

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Re: Discussion of Intense Tropical Cyclones

#121 Postby 1900hurricane » Thu Feb 16, 2017 11:38 pm

The Bulletin of the American Meteorological Society has a new paper on Patricia up.

Re-Writing the Tropical Record Books: The Extraordinary Intensification of Hurricane Patricia (2015)
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Re: Discussion of Intense Tropical Cyclones

#122 Postby 1900hurricane » Fri Feb 17, 2017 12:07 am

mrbagyo wrote:Was the 890 mb reading on STY Betty (August 1987 - recon farewell) just an estimate or recon data. Because if its recon, IMO, 140 knots is pretty low for such a compact tight storm. The reanalysis of Knaff would be pretty decent estimate(170+ knots peak).

Landfall intensity in best track is 135 I guess, that's just 5 knot reduction from peak. I think it's possible that Betty actually made landfall in N Samar as a Cat5 instead of "just" being a strong cat 4.

Betty doesnt possess the most impressive CDO but men, she is one tight system and there was also a strong ridging to its north that forced her to take a west track. Any thoughts?

The 1987 Joint Typhoon Warning Center Annual Tropical Cyclone Report doesn't explicitly mention that it was recon measured, but it can be inferred with reasonable confidence from the wording that it "had the lowest reported minimum sea-level pressure [of the year] (891 mb)." Unlike many of the other JTWC reports, the 1987 report doesn't list all the recon fixes for the year, but Nina was also estimated to have had a pressure of 891 mb (AH77 output for 145 kt), so that in itself is noteworthy enough to reasonably conclude that the 891 mb was a direct recon measurement.

It is also noteworthy that you brought up the appearance of Betty's CDO. It's not like it's horrible, but it wouldn't be something I would expect a pressure below 900 mb in on a glance. Flo '90 is another one of those storms, which had a recon measured 891 mb as well. Betty '87 and Flo '90 are pictured at peak intensity below, respectively. Storms like these are just a couple of examples that show how much more we still have to learn about tropical cyclones.

Image

Image
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Re: Discussion of Intense Tropical Cyclones

#123 Postby CrazyC83 » Wed May 10, 2017 11:35 pm

1900hurricane wrote:
tatertawt24 wrote:
1900hurricane wrote:I think one of the problems with the ADT study is the assumption that the most intense tropical cyclones of the satellite era were all rated at a category 5 intensity (since every system in that study was of SSHWS category 5 intensity with the lone exception of Hellen '14). It sounds weird to say at first, but several of the basins that didn't have recon early in the satellite era had some rather intense storms that were more than likely held down by Dvorak constraints. Early geostationary satellite resolution probably didn't help either. Possibly two of the most egregious cases are from Meli (SPac, 1979) and Raymond (EPac, 1983), which are both pictured below, respectively.

Image

Image

With that said, it is not an easy problem to address. Honestly, the other tropical cyclone basins probably need some sort of reanalysis project like what is currently being done for the Atlantic basin implemented. We know much more about tropical cyclones now than we ever did before, so reanalysis will likely go a long way in bettering the tropical cyclone climatology, especially at the higher intensities. However, as has been seen in the ATL reanalysis, these projects can take a very long time and a large number of resources to complete.


Agree with Meli but Raymond doesn't look terribly impressive imo. Tiny Wilma-esque eye but kind of ugly otherwise. :lol:

I would tend to agree that Meli is more likely to be the stronger of the two, but Raymond is likely no slouch. The CMG CDO yields a starting DT of 6.5, so any eye adjustment already brings the system up to a DT of 7.0. GOES 5 image resolution leaves something to be desired, but AVHRR imagery from around the same time shows at least an OW eye, and even this pass isn't ideal since the eye is somewhat near the edge, meaning a WMG eye (and thus a DT of 7.5) is a possibility.

Image

At the very least, it's easy to conclude that Raymond was likely more intense than its currently listed 125 kt peak intensity. In fact, Raymond was possibly the third of a trio of EPac SSHWS category 5s from 1983 that were not analyzed as so, following Barbara and Kiko.


I'm just going through these, but I would estimate Meli at 175 kt (clear T8.0; probably the S.Hem record holder) and Raymond at 150 kt (clear T7.0, but not quite T7.5) based on those imagery.

Recent storms - especially Megi, Haiyan and Patricia - have made us learn a lot more about the most extreme storms. There is often a low bias in Dvorak at the high end, and sometimes T8.0 is indeed broken. The Recon data from Megi and Patricia, plus analyzed data from Haiyan via surface obs, are extremely valuable. BTW I did an estimation on Haiyan's lowest pressure - using a 185 kt intensity I got 880 mb using the KZC method, while using the Schloemer equation from storm chaser data on land I got the main landfall pressuure at 897 mb.
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Re: Discussion of Intense Tropical Cyclones

#124 Postby WAcyclone » Thu Jul 06, 2017 3:05 pm

Apparently, Cyclone Winston from 2016 has been reanalyzed by RSMC Nadi. With 150 knots it is now officially considered the strongest TC worldwide in terms of 10-minute sustained wind speed (surpassing Typhoon Tip's 140 kt). However, Hurricane Patricia's 1-minute wind speed of 185 knots would of course lead to a higher value when converted to 10-minute winds. The central pressure has also been lowered to 884 mb which is a record for the southern hemisphere. I am not sure if I would agree with these changes but the observations from Vanua Balavu (which occurred before peak) might support such an incredible intensity. The Dvorak study from Velden et al. found Cyclone Pam to be stronger and more intense than Winston though.

Any opinions about this quite significant change?

 https://twitter.com/Cyclonebiskit/status/882986235022774273




The radar presentation was almost perfect but I have seen more impressive BD IR images:

Image

Image

This is the first post from a long-time lurker :D
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Re: Discussion of Intense Tropical Cyclones

#125 Postby 1900hurricane » Thu Jul 06, 2017 7:00 pm

Heh, not a bad first post! Image

I'm curious as to why Nadi decided to reanalyze Winston '16 with such an aggressive intensity. I can see that they have changed the best track (found here), but I wonder if their methodology is or will be explained in some sort of report. Using the standard 1.14 ration between 1 and 10 minute sustained winds, 150 kt 10 minute winds converts to 171 kt one minute winds. 150 kt/884 mb is carried for 00Z and 03Z on February 20th, while the 06Z intensity in the best track is listed at 150 kt/886 mb.

ADT was initially very high with Winston around the time of peak intensity, but the ADT algorithm changed from the EPac version to the WPac version when the system crossed the International Date Line, tanking the numbers by over half a T in the process. I imagine ADT was a big factor when JTWC originally put the 00Z February 20th intensity at 160 kt, and I also believe that the algorithm change is what caused them to take that intensity back. As I believe I've stated before, I'm not a fan of having two different ADT algorithms for each side of the International Date Line, but I certainly could learn some more on the subject as to why ADT is set up that way.

Aside from the EPac ADT, most objective intensity estimates weren't exactly smitten with Winston. The SATCON mean only yielded lower end SSHWS category 5 intensities around peak intensity, although it should be noted that CIMSS's ADT was re-run only using the WPac ADT. Still though, AMSU and the other microwave imagers did SATCON no favors. Winston did receive one very high SSMIS score >100 on February 20th, but it strangely did not translate to an actual intensity estimate greater than 140 kt per the CIMSS SATCON graph.

Image

I would have to think that such an intensity estimate would have to lean heavily on the Dvorak Technique, EPac ADT, and/or surface observations. The last one particularly interests me, especially considering the only surface observations that I am aware of from Fiji were those posted in the original Winston thread. If Nadi has numbers that I haven't seen, I wouldn't be surprised at all if they supported such an intensity.
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Re: Discussion of Intense Tropical Cyclones

#126 Postby Blinhart » Fri Jul 07, 2017 12:42 am

Is this the storm that messed up Survivor?
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Re: Discussion of Intense Tropical Cyclones

#127 Postby WAcyclone » Fri Jul 07, 2017 9:18 am

Thanks a lot for your in-depth analysis of the satellite intensity estimates, 1900hurricane!

As you pointed out, there really isn't much support for the 150 kt peak when just taking the satellite presentation into account. Therefore, my guess would be that Cyclone Winston's record-setting intensity was estimated mostly based on surface observations which makes it an extremely interesting case in my opinion. Below is a graph of the highest wind speeds and gusts recorded during February 20th:

Image

However, the stations of Vanuabalavu, Koro (probably the best-positioned station), Kubulau, Rakiraki, Yaqara and Viwa were all destroyed (marked with red) during Winston's passage as is shown in this graphic:

Image
Source

The 125 kt reading from Vanuabalavu is obviously the most interesting observation (but also note the 116 kt from Levuka which was recorded quite a bit away from the inner eyewall). Here is an interesting excerpt from the Fiji Climate Summary source given above:

"During tropical cyclone Winston, Vanuabalavu recorded sustained winds of up to 233 km/hr (125 knots) and gusts of up to 306 km/hr (165 knots), before winds toppled the station and systems stopped communicating. This makes it the highest ever sustained wind and gust to be recorded at land based station in Fiji. However, it is possible that Winston could have resulted in stronger winds over Fiji than the maximum that got recorded at Vanuabalavu as all other land based stations (including Vanuabalavu), which lay in the path of Winston, could not survive the full life of the cyclone."

At the time of the reading (18z on February 19th or 6am local time on February 20th), Cyclone Winston looked like this on IR BD imagery:

Image

I unfortunately don't have access to the best track data but it might be interesting to know what Nadi estimated for 18z February 19th.
There now are several factors which can contribute to a very high peak intensity estimate based on that 125 kt reading (provided it is valid of course):

1) It can be assumed that the Vanuabalavu station did not record the strongest winds at its location before the equipment failed (like already discussed by Nadi in the Climate Summary source).

2) The station was almost perfectly located in the left-front quadrant of the cyclone but it may nevertheless have underestimated the maximum windspeed at that time by a few percent (see Nolan et al.).

3) Land friction effects could also lead to a higher estimate for peak intensity.

4) Maybe most importantly: Winston clearly strengthened after passing Vanuabalavu. The evolution between 18z (time of observation) and 03z (time of peak intensity according to Nadi) was impressive, especially in terms of symmetry and eye structure:

Image

All these points considered, I think 150 kt may be reasonable if the Vanuabalavu reading is valid (not caused by wind-tunnel effects etc.). However, it is still quite unusual for an official agency to estimate 150 kt based on a 125 kt observation. I certainly would like to see a new report by Nadi as well. Maybe they have also taken damage patterns into account. Who knows...
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Re: Discussion of Intense Tropical Cyclones

#128 Postby NotoSans » Sat Jul 08, 2017 11:15 am

The reanalyzed value of 150 knots was based mainly on Dvorak estimates. I personally disagree with a CI value of 8.0 and find the intensity estimate from the FMS a little bit too high.

With respect to TC Winston, the Nadi RSMC has now completed their reanalysis of the intensity of TC Winston. They have now found a peak intensity wind of 150 knots with peak minimum central pressures in the 884-886 hPa range (Nadi adjusted its TC module to come up with the revised minimum central pressure data). When performing Dvorak Analysis, the following were arrived at:

At 20/02:0000UTC - Analysis based on Warm Medium Grey (WMG) Eye in Cold Medium Grey (CMG) Surr with banding yields a Current Intensity(CI) value of 8.0. A CI value of 8.0 yields 10-minute mean wind intensity of 150 knots (as opposed to the original value of 160 knots) A CI value of 8.0 was analyzed from 20/02:0000UTC till 20/02: 0600UTC.

Nadi recognized that their original pressure values needed to be revisited, and so they readjusted their TC Module columns/figures inputs in order correct the pressures.
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Re: Discussion of Intense Tropical Cyclones

#129 Postby Ptarmigan » Sat Jul 08, 2017 1:59 pm

Tropical Cyclone Winston looks impressive on satellite and Doppler radar.

It has to be Category 5 tropical cyclone with winds of 160 to 175 knots (185 to 200 mph). I know land interacting reduces sustained winds, while gusts go up.

It is most preferable that they be measured directly, not by satellite. I know for most areas, it is not practical to fly into these tropical cyclones.
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Re: Discussion of Intense Tropical Cyclones

#130 Postby 1900hurricane » Sat Jul 08, 2017 11:23 pm

NotoSans wrote:The reanalyzed value of 150 knots was based mainly on Dvorak estimates. I personally disagree with a CI value of 8.0 and find the intensity estimate from the FMS a little bit too high.

With respect to TC Winston, the Nadi RSMC has now completed their reanalysis of the intensity of TC Winston. They have now found a peak intensity wind of 150 knots with peak minimum central pressures in the 884-886 hPa range (Nadi adjusted its TC module to come up with the revised minimum central pressure data). When performing Dvorak Analysis, the following were arrived at:

At 20/02:0000UTC - Analysis based on Warm Medium Grey (WMG) Eye in Cold Medium Grey (CMG) Surr with banding yields a Current Intensity(CI) value of 8.0. A CI value of 8.0 yields 10-minute mean wind intensity of 150 knots (as opposed to the original value of 160 knots) A CI value of 8.0 was analyzed from 20/02:0000UTC till 20/02: 0600UTC.

Nadi recognized that their original pressure values needed to be revisited, and so they readjusted their TC Module columns/figures inputs in order correct the pressures.

Interesting. I was a little suspicious of that just based on the 150 kt being the T8.0 intensity. It's interesting that Nadi added for a banding feature since I didn't really see a good enough band to add for one near peak intensity. If they're adding for banding, that also assumes the Model Expected T# was at 8.0.

I can see one Dvorak analysis at the 8.0 intensity on the SATCON graph I have posted above. I guess that was Nadi's.
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Re: Discussion of Intense Tropical Cyclones

#131 Postby 1900hurricane » Mon Jul 17, 2017 10:44 pm

Regarding the Dvorak Technique, there is something I have been pondering: Cold Dark Grey rules. Rules for CDG don't technically exist when using the Dvorak Technique's EIR Eye Pattern to derive a Data T. It is said (but I cannot actually verify) that when first implementing the Dvorak Technique for estimating the intensities for Atlantic tropical cyclones, Vernon Dvorak did not believe a mature tropical cyclone could maintain the CDG tops in an organized manner, and thus no CDG rules were needed. The official Dvorak EIR Eye Pattern Diagram to derive a DT is provided below:

Image

The Dvorak Technique has long been implemented worldwide, including in places with a higher and colder tropopause than the tropical Atlantic, places that can support organized CDG convective tops in certain instances. As far as I can tell, everyone has followed the original Dvorak Technique's DTs, including for convective maulers like Nida '09 (image), Haiyan '13 (image) and Nuri '14 (image), up until rather recently. In December 2014, SAB utilized the first unofficial CDG rules that I am aware of for Typhoon Hagupit. They also went back to these unofficial rules for Severe Tropical Cyclone Pam in March of 2015. Images of both systems, respectively, at the time the unofficial CDG rules were used are provided below.

Image

Image

Based on these cases, it appears that SAB's CDG rules first involves giving the CDG embedded shade an eye number of 7.0, which is a reasonable extrapolation based on the existing framework. However, it is curious that Hagupit's medium grey eye received a 0.5 eye adjustment to arrive at a DT of 7.5. This is the same eye adjustment that Pam received for an off-white eye (two shades warmer than MG), meriting the same 7.5 DT. This is a little inconsistent with the existing eye adjustment procedures, since it takes a maximum of two shade colors of the eye to change the eye adjustment per each constant ring shade.

Are SAB's CDG rules correct? It's impossible to tell honestly due to the lack of direct observations in an already rare class of storms. I do think SAB's CDG rules do have merit, but there are still lots of unanswered problems. Should Hagupit and Pam really get the same eye adjustment in the two cases already mentioned? What about a case like Patricia '15? Near the time of Patrica's supposed peak intensity, from after recon left until sunrise, Patricia's WMG eye (thank you polar orbiting satellites) was surrounded by CDG, but it appears it does not quite meet the (assumed) 0.5º/30 nm ring thickness to count as an embedded shade. Would a +1.5 eye adjustment for WMG/CDG work better than adding a 7.0 eye number for CDG (bringing the Patricia '15 example up to an 8.0 DT)? Could both be utilized perhaps? However, if both implemented though, a system like Haiyan '13 with a WMG eye and full CDG embedded shade would then receive a DT of 8.5 (which extrapolates to 185 kt). Would that be alright, or should the 8.0 ceiling be preserved?

Image

Image

This is all speculation, but this kind of speculation is largely why this thread exists. If you were charged with implementing some kind of new Cold Dark Grey rules to the Dvorak Technique's Eye Pattern, what would you do?
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Re: Discussion of Intense Tropical Cyclones

#132 Postby euro6208 » Sun Aug 13, 2017 7:46 am

I know there are several basins out there besides the WPAC but the WPAC leads the way in terms of maximum sustained winds and lowest pressures worldwide and this was during the recon era. That ended in 1987 and still the WPAC leads both category by a tenfold. What a loss. I can't imagine how many low pressures and high winds they would have found with recon. 100>1 (Out of nowhere Patricia, lone WHEM equivalent, Wilma not exactly great 2nd).
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Re: Discussion of Intense Tropical Cyclones

#133 Postby 404UserNotFound » Tue Aug 15, 2017 7:21 pm

Seeing that one GIF of Nepartak makes me wonder: how good of a method would photogrammetry be for estimating intensity? (Yes, I know it's the cloud tops, not the surface, but it could provide some sort of benchmark.)
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Re: Discussion of Intense Tropical Cyclones

#134 Postby 1900hurricane » Tue Aug 15, 2017 10:56 pm

404UserNotFound wrote:Seeing that one GIF of Nepartak makes me wonder: how good of a method would photogrammetry be for estimating intensity? (Yes, I know it's the cloud tops, not the surface, but it could provide some sort of benchmark.)

I assume you are referring to this one (long version here).

Image

I've actually been curious about it myself. Like you said, the cloud tops don't move at the same rate as the winds at the surface move, but you'd think some sort of relationship could be established. Himawari-8's target window may make it possible with its superior spatial and temporal resolution. However, I could see some issues present themselves. Shearing upper level winds or collapsing convection from a dry air intrusion could throw things out of whack. Even unbalanced outflow channels could present a challenge. For an apex tropical cyclone like Nepartak '16 and the others discussed in this thread, these issued may be less pressing though.

I've always thought of Nuri '14 as a violent spinner too. MTSAT's spatial and temporal resolution doesn't hold a candle to Himawari-8, especially the target window, but I've aways been struck at how profoundly it seems to capture Nuri's violent rotation.

Image
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Re: Discussion of Intense Tropical Cyclones

#135 Postby 1900hurricane » Tue Aug 15, 2017 11:15 pm

Also, here is a very preliminary version of my CDG rules. I did include both the 7.0 eye number for CDG and 1.5 eye adjustment for a WMG eye surrounded by CDG for now, meaning a DT of 8.5 can be achieved, breaking the original 8.0 ceiling. I'm not sure I'm going to stick with it, but recent data has indicated that the most intense tropical cyclones can exceed a T8.0 intensity estimate.

Image
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Re: Discussion of Intense Tropical Cyclones

#136 Postby euro6208 » Fri Aug 18, 2017 7:29 am

Yeah Nepartak is just one of a handful of typhoons that seem to intensify even further when you think it had peak (Warmer and shaper eye, colder tops, Higher dvorak and ADT's and a more incredible satellite presentation for a much longer time period). Unlike the other basins like Wilma and Patricia who peaked for a shorter period of time.
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Re: Discussion of Intense Tropical Cyclones

#137 Postby 1900hurricane » Tue Sep 05, 2017 3:17 pm

Just going to bump this for Irma. I'll have some more to say when I get a break, but recon confirmed 160 kt is crazy, especially considering the Data T never exceeded 6.5.
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Re: Discussion of Intense Tropical Cyclones

#138 Postby euro6208 » Tue Sep 05, 2017 4:09 pm

Safe to say that ADT and dvorak fails. 6.5 from both yields only a Cat 4 but it's already a high end 5. It beats every intensity consensus estimates.

Previous typhoons who peaked at 7.5 or higher likely were severely underestimated.
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Re: Discussion of Intense Tropical Cyclones

#139 Postby tolakram » Tue Sep 05, 2017 6:30 pm

1900hurricane wrote:Just going to bump this for Irma. I'll have some more to say when I get a break, but recon confirmed 160 kt is crazy, especially considering the Data T never exceeded 6.5.


The T numbers are based on IR which will vary from basin to basin right, or is this adjustment already figured in.
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Re: Discussion of Intense Tropical Cyclones

#140 Postby 1900hurricane » Tue Sep 05, 2017 6:46 pm

tolakram wrote:
1900hurricane wrote:Just going to bump this for Irma. I'll have some more to say when I get a break, but recon confirmed 160 kt is crazy, especially considering the Data T never exceeded 6.5.


The T numbers are based on IR which will vary from basin to basin right, or is this adjustment already figured in.

The average tropopause height/temperature does vary basin to basin with highest/coldest tropopauses generally found near the Maritime Continent. There is no scaling applied in the Dvorak Technique though. Data Ts only depend on which temperature thresholds are met. There is some scaling in ADT version 8.2.1 since a slightly different algorithm is used on each side of the International Date Line, although I personally am a little skeptical that two different relations are needed. Anyway, Vernon Dvorak used data primarily (exclusively?) from the NAtl when founding the technique, so in theory, the Dvorak Technique should be the most accurate in the NAtl.
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