source of USA_RMW in v04r00

ben s.

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Mar 14, 2019, 6:07:21 PM3/14/19

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Dear IBTrACS Team-

I have been working with the recently released v04r00 IBTrACS data (thank you!) and I was wondering where the data for USA_RMW is being sourced from? When I compare the USA_RMW to the extended best-track (http://rammb.cira.colostate.edu/research/tropical_cyclones/tc_extended_best_track_dataset/docs/ebtrk_readme.txt), I notice substantial differences in some cases (e.g., twice as large in USA_RMW compared to the extended best-track). Any insight would be helpful. Thank you as always for your time.

-Ben

Ken Knapp - NOAA Federal

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Mar 15, 2019, 8:16:26 AM3/15/19

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Hi Ben

So it is easier to track down your issue, could you provide an example of the differences that you're seeing?

Thanks-

-Ken

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Ken Knapp - NOAA Federal

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Mar 15, 2019, 8:42:14 AM3/15/19

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Hi Ben

I did some digging.

The source for the RMW is the working best track. The official HURDAT does not provide reanalyzed RMW (i.e., the HURDAT2 file), so we grab the RMW from the working best track. For instance, you can see the sources used for IRMA in the source table at:

http://www.atms.unca.edu/ibtracs/ibtracs_v04r00/index.php?name=v04r00-2017228N14314

It lists the HURDAT2 file and the working best track. The working best track file is available from NHC here:

ftp://ftp.nhc.noaa.gov/atcf/archive/2017/

When I look at IRMA at 08/24 06Z,

IBTrACS RMW = 30 nm (see link above ... all IBTrACS data is in table near bottom of page)

NHC RMW = 30 nm (see FTP above of bal09)

CIRA Extended best track = 60 nm

So I don't know why the RMW in IBTrACS differs from the Extended best track, but IBTrACS agrees with the best track file at NHC. It is interesting to note that the RMW does agree for other times of IRMA, but not at 082106.

I will forward this question to CIRA.

Thanks-

-Ken

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Ken Knapp - NOAA Federal

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Mar 15, 2019, 9:04:25 AM3/15/19

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BTW ... The example is from HARVEY, not IRMA, sorry for any confusion, dates/and times are correct for HARVEY.

-Ken

ben s.

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Mar 15, 2019, 10:34:44 AM3/15/19

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Hi Ken-

Sorry for not providing an example. As you pointed out, the differences are sometimes large. It would be one thing if the differences were 5–10 nm, but 30 nm seems quite large at least to me. I was going to followup with John anyways because I think I noticed some typos in the Extended Best-Track as well. As an example of an error in the Extended Best-Track:

AL0399 BRET      082306 1999 27.0  97.9  80  963  15 -99 1009 125  90 90 75 75  60 40 25 25  25 20 15 15 *   -51.
AL0399 BRET      082312 1999 27.3  98.3  60  980  50 -99 1010 125 100100 25 25 -99-99-99-99   0  0  0  0 *   -91.
AL0399 BRET      082318 1999 27.6  98.8  35  993 305 -99 1010 125 100100 50 50   0  0  0  0   0  0  0  0 *  -145.

The radius of maximum winds for Bret on the last line is listed as 305 nm when the radius of tropical storm force winds only extend outwards to 100 nm. Moreover, Bret's RMW was only 50 nm in the previous advisory. Seems like a potential typo. Sorry again and thanks for the quick follow up.

-Ben

Jim Kossin

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Mar 15, 2019, 11:21:32 AM3/15/19

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As a related aside, I had asked Mark DeMaria sometime back what kind of QC they do on the operational and best-tracked wind radii. I don't think they do much, and in some cases they are unphysical. Not just having wind radii that are inside each other in an illogical way, but quite often they would represent a highly inertially unstable wind profile (decay more steeply than 1/r), which wouldn't exist for long, at least under order-1 axisymmetric assumptions. Might be a place where ibtracs can offer a value-added set of radii that are flagged when they are unphysical. --Jim

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Ken Knapp - NOAA Federal

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Mar 19, 2019, 3:30:54 PM3/19/19

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Hi Ben-

Thanks for your patience as we looked into this. The RMW information can differ between IBTrACS and the extended best track. Here's what I learned from those more familiar with extended best track

IBTrACS RMW - Source data is NHC ATCF b-deck (best track) files. As time goes on the best track can be modified.

Extended best track RMW - Source data is the CARQ in the A-decks (advisories). CARQ is primarily for running guidance, and is issued at that forecast time, where as the working best track and final best track are in flux.

So it appears that later modifications and corrections are applied to the best track but not to CARQ, hence the difference.

I hope this helps.

-Ken

ben s.

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Mar 19, 2019, 4:06:26 PM3/19/19

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Hi Ken-

Thanks for your input and time. Your answer is very helpful.

-Ben

Dan Chavas

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Mar 5, 2025, 10:58:15 AMMar 5

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Hi Ken,

I found myself in this thread while searching for more info about RMW sources in IBTrACS. Based on the above, I believe IBTrACS RMW is from HURDAT2 for 2021+ (when it is included because it has been Best Tracked) and then b-deck before then -- is that correct? If so, can you update the IBTrACS documentation to state this?

Right now it's not stated anywhere as far as I can tell. This issue of RMW data sourcing in HURDAT2 vs. IBTrACS vs. Extended Best Track (whose documentation does explain its RMW sources) is important and causing a lot of confusion for people.

Thanks! And thank you for all your hard work with this IBTrACS database.

Dan

Jennifer Gahtan - NOAA Federal

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Mar 10, 2025, 1:32:11 PMMar 10

to Dan Chavas, IBTrACS Q&A

Hi Dan,

IBTrACS prioritizes use of the HURDAT2 RMW where available and the b-deck where it is not. This means that the 2021+ RMW is from HURDAT2. Prior to this the majority of the data is from the b-deck, however in the February 2024 update of HURDAT2, RMW for some best tracks of Historical Atlantic TCs that impact the US (work of Delián Colón Burgos) were added to HURDAT2 and subsequently IBTrACS. These are often co-located with Landfall times and at most a few times per storm. We do not have this marked within the data itself, but recommend going back to the source if a specific USA dataset for RMW is desired.

Thanks for bringing this confusion to our attention and we will update documentation to reflect this information.

Jennifer

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