2017 TCRs

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Re: 2017 TCRs

#101 Postby Shell Mound » Thu Mar 08, 2018 6:55 pm

CrazyC83 wrote:
NotoSans wrote:Lee has been released. Peak intensity remains at 100 kt.
https://www.nhc.noaa.gov/data/tcr/AL142017_Lee.pdf


TAFB only supported T5.0 (90 kt) so that is likely why they kept it there. I know SAB was T5.5 and CIMSS was around T5.7.

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Lee certainly appears to have been stronger than 65-75 knots between 06:00 UTC and 12:00 UTC on 24 September 2017. Out of all the satellite fixes, the AMSUB estimate of ~90 knots best fits the outflow pattern, compact CDO, and small, distinct, stadium-effect eye. Personally, I think a case can be made that Lee was a major hurricane at this time, at least three days earlier than officially indicated in the TCR. Its presentation is among the most impressive I've seen, considering its minuscule size at the time of these frames. The lack of reconnaissance and remote sensing, especially drones, truly hindered the Hurricane Center, since only the AMSUB estimate may have come somewhat close to capturing the true intensity on 24 September.
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Re: 2017 TCRs

#102 Postby cycloneye » Fri Mar 09, 2018 9:36 am

Tropical Storm Bret and Hurricane Jose reports are up.
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Re: 2017 TCRs

#103 Postby NotoSans » Fri Mar 09, 2018 9:48 am

Surprised to see Jose maintained at C4 strength.
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Re: 2017 TCRs

#104 Postby Alyono » Fri Mar 09, 2018 10:28 am

I fail to understand the logic of keeping Jose as a category 4
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Re: 2017 TCRs

#105 Postby CrazyC83 » Fri Mar 09, 2018 11:26 am

Looking through the data for Jose, I agree that it should be at least 140 kt. I think they were trying to avoid a posthumous upgrade as much as possible.

The SFMR of 142 looked very reasonable to me, and that *alone* would support 140-145 kt. Even if that data is discarded, the Dvorak ratings were higher at 1800Z (between the Recon passes) than at either 1200Z or 0000Z. If you use 135 kt at 0000Z, then at 1800Z it should be 140 kt just on satellite interpretation.

I would have gone with a peak intensity of 145 kt at 1800Z as a result (with a reasonable range being 140-150 kt). The minimum pressure I would have set at 935 mb at that time on the same basis.
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Re: 2017 TCRs

#106 Postby Shell Mound » Fri Mar 09, 2018 11:44 am

CrazyC83 wrote:Looking through the data for Jose, I agree that it should be at least 140 kt. I think they were trying to avoid a posthumous upgrade as much as possible.

The SFMR of 142 looked very reasonable to me, and that *alone* would support 140-145 kt. Even if that data is discarded, the Dvorak ratings were higher at 1800Z (between the Recon passes) than at either 1200Z or 0000Z. If you use 135 kt at 0000Z, then at 1800Z it should be 140 kt just on satellite interpretation.

I would have gone with a peak intensity of 145 kt at 1800Z as a result (with a reasonable range being 140-150 kt). The minimum pressure I would have set at 935 mb at that time on the same basis.

From page 4 of the TCR:
Jose’s estimated peak intensity of 135 kt from 1800 UTC 8 September to 0000 UTC 9 September is based on a blend of SFMR and flight-level aircraft data from two consecutive Air Force Reserve Hurricane Hunter missions. During the first mission, the aircraft measured peak 700-mb flight-level winds of 146 kt and 142 kt at 1208 UTC and 1356 UTC 8 September, respectively, which equate to an intensity of about 130 kt. The highest “unflagged” SFMR measurement during the same flight was 125 kt. On the next flight, the plane measured a slightly lower peak 700-mb flight-level wind of 135 kt at 0026 UTC 9 September. The highest SFMR measurement was 142 kt a few minutes later, however this observation was surrounded by multiple flagged values and data dropouts, making the measurement somewhat questionable. Without entirely discounting this measurement, Jose’s maximum intensity is estimated to be 135 kt, which is a blend of the SFMR data and the highest flight-level-adjusted winds.

I actually think the reasoning for the intensities at the time of the two aircraft fixes (at 12:08–13:56 UTC/8 September and 00:26 UTC/9 September, respectively) is sound. The SFMR readings were not as reliable as I originally suspected, as I was unaware of the flagged readings, which give added context. I do support the intensities of 130 and 135 knots at 12:00 UTC/8 September and 00:00 UTC/9 September. The major issue, as you mentioned, is that the satellite estimates were higher around 18:00 UTC than at 00:00 UTC, which would support an increase of about five knots. To cite one past example from the Atlantic basin: the Hurricane Center used satellite estimates to derive Danny's 110-knot peak intensity in 2015, as the reconnaissance data supported 100 knots several hours after the satellite presentation had degraded substantially. The NHC also followed a similar reasoning in its assessment of Patricia's (2015) maximum intensity over the eastern North Pacific. Thus, the failure to apply similar scientific reasoning in this case is inconsistent with past practice, and may harm efforts to introduce consistency and accuracy to global tropical-cyclone records. It corrupts the data.

Why do you think "they were trying to avoid a posthumous upgrade"? The NHC has upgraded a number of storms, including Emily of 2005 (to 140 knots) and Otto of 2016 (to 100 knots).
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Re: 2017 TCRs

#107 Postby CrazyC83 » Fri Mar 09, 2018 2:07 pm

Shell Mound wrote:
CrazyC83 wrote:Looking through the data for Jose, I agree that it should be at least 140 kt. I think they were trying to avoid a posthumous upgrade as much as possible.

The SFMR of 142 looked very reasonable to me, and that *alone* would support 140-145 kt. Even if that data is discarded, the Dvorak ratings were higher at 1800Z (between the Recon passes) than at either 1200Z or 0000Z. If you use 135 kt at 0000Z, then at 1800Z it should be 140 kt just on satellite interpretation.

I would have gone with a peak intensity of 145 kt at 1800Z as a result (with a reasonable range being 140-150 kt). The minimum pressure I would have set at 935 mb at that time on the same basis.

From page 4 of the TCR:
Jose’s estimated peak intensity of 135 kt from 1800 UTC 8 September to 0000 UTC 9 September is based on a blend of SFMR and flight-level aircraft data from two consecutive Air Force Reserve Hurricane Hunter missions. During the first mission, the aircraft measured peak 700-mb flight-level winds of 146 kt and 142 kt at 1208 UTC and 1356 UTC 8 September, respectively, which equate to an intensity of about 130 kt. The highest “unflagged” SFMR measurement during the same flight was 125 kt. On the next flight, the plane measured a slightly lower peak 700-mb flight-level wind of 135 kt at 0026 UTC 9 September. The highest SFMR measurement was 142 kt a few minutes later, however this observation was surrounded by multiple flagged values and data dropouts, making the measurement somewhat questionable. Without entirely discounting this measurement, Jose’s maximum intensity is estimated to be 135 kt, which is a blend of the SFMR data and the highest flight-level-adjusted winds.

I actually think the reasoning for the intensities at the time of the two aircraft fixes (at 12:08–13:56 UTC/8 September and 00:26 UTC/9 September, respectively) is sound. The SFMR readings were not as reliable as I originally suspected, as I was unaware of the flagged readings, which give added context. I do support the intensities of 130 and 135 knots at 12:00 UTC/8 September and 00:00 UTC/9 September. The major issue, as you mentioned, is that the satellite estimates were higher around 18:00 UTC than at 00:00 UTC, which would support an increase of about five knots. To cite one past example from the Atlantic basin: the Hurricane Center used satellite estimates to derive Danny's 110-knot peak intensity in 2015, as the reconnaissance data supported 100 knots several hours after the satellite presentation had degraded substantially. The NHC also followed a similar reasoning in its assessment of Patricia's (2015) maximum intensity over the eastern North Pacific. Thus, the failure to apply similar scientific reasoning in this case is inconsistent with past practice, and may harm efforts to introduce consistency and accuracy to global tropical-cyclone records. It corrupts the data.

Why do you think "they were trying to avoid a posthumous upgrade"? The NHC has upgraded a number of storms, including Emily of 2005 (to 140 knots) and Otto of 2016 (to 100 knots).


Emily was the only case I know of that a storm jumped from 4 to 5 in post-analysis. Indeed, the 1800Z intensity is what is most questionable - the 1200Z intensity was probably accurate (either 130 or 135), while the 0000Z intensity the reasoning may need further investigation. I know there were flagged 149 kt SFMR readings as well in the flight around 1400Z, but I was never sure about their accuracy (they were not mentioned in the report).
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Re: 2017 TCRs

#108 Postby Chris90 » Fri Mar 09, 2018 3:01 pm

Regarding Jose, I understand their reasoning on why they considered the 142kt sfmr suspect, but there was a dropsonde in the NE eyewall that supported it, in my opinion.
The sonde measured a peak wind of 177kts 46mb above the surface, as well as 175kts at the 925mb level, which was 31mb/286m above the surface. The average wind was 162kts over the lowest 500m, and 153kts over the lowest 150m.

That data, especially the averages, to me, supports the 142kts sfmr, even if there was data dropouts and flagged values.
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Re: 2017 TCRs

#109 Postby cycloneye » Fri Mar 09, 2018 8:08 pm

I am posting some tweets from Eric Webb,Eric Blake and Philippe Papin that turned into a interesting discussion.

 https://twitter.com/wxtrackercody/status/972210497717178368




@webberweather
Yeah I don't understand how this wasn't raised to at least 140 KT especially given Jose was a small TC and capable of rapid intensity fluctuations and thus spinning down very quickly by the time recon got there.

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@EricBlake12
There are some science questions that have been raised this year by SFMR data at very high wind speeds. It is possible it is a little too hot at Cat 5 winds- remember the calibration points up there are few and far between

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@pppapin
I was always under the impression that #SFMR performs the best at high wind speeds, but perhaps the algorithm may suffer from lack of data points at >140kt.

Of course the dropsonde launched in the NE quad w/ that mission failed, so no way to validate SFMR there

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@EricBlake12
Indeed- As was I. For years it has problems even measuring the very high winds- had a documented low bias. But the algorithm was changed 2 years ago- possible it went too far but hard to say without a full study.

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@pppapin
I thought the algorithm change was mainly to reduce the high bias SFMR had in high rain-rate scenarios for TS wind speeds (as in Klotz and Uhlhorn 2014: https://journals.ametsoc.org/doi/pdf/10 ... 14-00028.1 … …)

From that paper, it looks like these flagged SFMR obs are related to noisy Tb from the radiometer.

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@EricBlake12
Replying to @pppapin @webberweather @wxtrackercody
Yep the main fixes were for weaker winds. But it affected the whole spectrum of winds- it really is a challenge because dropsonde failure rate is very high at Cat 5 winds. Plus they may or may not hit the RMW. Tricky tricky problem

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Re: 2017 TCRs

#110 Postby Chris90 » Fri Mar 09, 2018 8:28 pm

Thank you for posting that cycloneye.

Interesting discussion, and now I'm wondering if they are questioning Irma's 160kt sfmr. I wonder if they are questioning the performance of the sfmr based off comparing it with CYGNSS data. I know I read last September that they were timing some recon missions with CYGNSS flyovers to get data sets that were timed close together so they could compare recon findings with what CYGNSS was finding.

Also, does anyone know what exactly counts as the dropsonde failing? Phillippe Papin said the sonde in the NE eyewall failed in Jose, but the data I looked at went all the way to the surface.
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Re: 2017 TCRs

#111 Postby 1900hurricane » Fri Mar 09, 2018 9:45 pm

The SFMR algorithm change and the possible repercussions is interesting. This is something that could impact Irma in particular since the operational SFMR estimates were very close to the flight level winds for a great length of time. Based on the Twitter conversation above, it sounds like the change in SFMR occurred after the 2015 season (although I don't know for sure if this assumption is correct), meaning this could also have an impact on Hurricane Matthew from the 2016 season. Like Eric Blake mentioned, we can't know for sure without a full study.
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Re: 2017 TCRs

#112 Postby Shell Mound » Fri Mar 09, 2018 10:42 pm

For cases such as this, a reanalysis probably is in order, based on the evolving state of research. There are simply a large number of variables that affect estimates of intensity, including eye diameter, satellite angle, background pressure, intensity trend, and forward speed. Satellite data often fail to reflect the true intensity of compact systems such as Patricia (2015) and Jose. I do note that the peak DVORAK presentation of Jose was quite similar to Igor's in 2010, and there is ample, albeit circumstantial, evidence that Igor probably reached 140 knots (Cat 5) at one point. Since Jose was smaller than Igor and embedded in high environmental pressure, it was very likely of similar or stronger intensity. A similarly compact system with a less impressive appearance at its peak was Joaquin (2015), which, given its rapid intensification and subsequent weakening, probably briefly attained Cat-5 status between reconnaissance fixes. Incidentally, Robbie Berg wrote the TCR for Joaquin as well as Jose.
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Re: 2017 TCRs

#113 Postby Alyono » Sat Mar 10, 2018 12:55 am

as fr Irma, there was the surface observation that seemed to confirm the SFMR winds on St Barthelemy
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Re: 2017 TCRs

#114 Postby CrazyC83 » Sun Mar 11, 2018 5:36 pm

Chris90 wrote:Thank you for posting that cycloneye.

Interesting discussion, and now I'm wondering if they are questioning Irma's 160kt sfmr. I wonder if they are questioning the performance of the sfmr based off comparing it with CYGNSS data. I know I read last September that they were timing some recon missions with CYGNSS flyovers to get data sets that were timed close together so they could compare recon findings with what CYGNSS was finding.

Also, does anyone know what exactly counts as the dropsonde failing? Phillippe Papin said the sonde in the NE eyewall failed in Jose, but the data I looked at went all the way to the surface.


Even the flight level winds for Irma - peaking at 171 kt - support a 155 kt intensity at least.
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Re: 2017 TCRs

#115 Postby NotoSans » Mon Mar 12, 2018 9:16 am

https://www.nhc.noaa.gov/data/tcr/AL112017_Irma.pdf
Hurricane Irma is out - peak intensity lowered to 155kt in favor of fight-level wind speeds.
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Re: 2017 TCRs (Irma peak intensity lowered to 155kt)

#116 Postby CrazyC83 » Mon Mar 12, 2018 9:27 am

Interesting re: Irma, I guess there will need to be better investigations between SFMR and flight level winds at extreme intensities. I wonder if they might drop Maria to 145 kt on the same basis?
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Re: 2017 TCRs (Irma peak intensity lowered to 155kt)

#117 Postby NotoSans » Mon Mar 12, 2018 9:30 am

I’m interested to see whether they will revise the peak intensity of Matthew’16 on a similar basis.
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Re: 2017 TCRs (Irma peak intensity lowered to 155kt)

#118 Postby cycloneye » Mon Mar 12, 2018 9:35 am

I knew Maria was going to be the last report to be released of the biggies of 2017 because of the good deal of data of the Puerto Rico landfall.Based on what has transpired with Jose and Irma reports,I guess it will be cat 4 at landfall unless something surprising appears in the data.
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Re: 2017 TCRs (Irma peak intensity lowered to 155kt)

#119 Postby SouthDadeFish » Mon Mar 12, 2018 9:53 am

In regard to the maximum intensities of the most intense storms last year (e.g., Harvey, Irma, Jose, and Maria), we still have a lot to learn about the science of the wind profiles, among other things, in these storms. The SFMR measures ocean brightness temperature at six different C-band channels. It doesn't directly measure wind speed. We use these brightness temperatures to estimate the surface wind speed. It's quite possible at very large wind speeds, the emulsion that is the ocean surface behaves slightly differently than say Cat 3/4 wind speeds. It could be that the SFMR has a high-bias in these cases, or it could be that the surface wind speeds can actually become comparable to flight-level wind speeds in these cases. We need to gain a better understanding of the physics of these very intense storms. For now, I agree with the NHC for going with 155 kt for the peak intensity. It is a good compromise. At the end of the day, the difference between 155 or 160 kt is well within the margin of error for NHC intensity estimates.
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Re: 2017 TCRs (Irma peak intensity lowered to 155kt)

#120 Postby 1900hurricane » Mon Mar 12, 2018 10:00 am

The Irma report slashes over 2.5 units of ACE and over 5.5(!) units of PDI from Irma, by far the most drastic post season change with regards to those metrics.

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