2018 JTWC BST - Discussion

[Nancy Smar]

https://www.metoc.navy.mil/jtwc/jtwc.html?best-tracks
JTWC published its BST just now, and there are many interesting changes in the BST, let us have a discussion on these changes.

[Nancy Smar]

WP, 03, 2018033012, , BEST, 0, 168N, 1391E, 130, 926, ST
WP, 10, 2018070818, , BEST, 0, 211N, 1351E, 145, 910, ST,
WP, 25, 2018083106, , BEST, 0, 182N, 1427E, 155, 907, ST
WP, 26, 2018091212, , BEST, 0, 142N, 1339E, 155, 896, ST
WP, 26, 2018091318, , BEST, 0, 153N, 1279E, 155, 897, ST,
WP, 28, 2018092418, , BEST, 0, 195N, 1290E, 140, 914, ST,
WP, 30, 2018100118, , BEST, 0, 173N, 1336E, 150, 906, ST

[Nancy Smar]

WP, 31, 2018102418, , BEST, 0, 153N, 1452E, 150, 904, ST
SH, 15, 2018032118, , BEST, 0, 155S, 1083E, 150, 906, ST

[1900hurricane]

Interesting moves. I like some of them, but some of them are just weird. Here's some of my thoughts on a first glance.

The Maria edits look ok for the most part. I probably would have retained the 140 kt for the initial peak, but I'm not up in arms about 135 kt, especially given how fast it suddenly had the DT of 7.0. The bump to the 145 kt second and overall peak actually looks very similar to the mock up best track I had at the end of the Maria thread. I still think surface obs supported 65 kt at Guam landfall at 18Z July 4th (the operational 55 kt was retained for that point).

I'm ok with 155 kt for Jebi. I might have kept it at 150 kt, but SATCON perhaps supported a bump even if IR wasn't traditional DT 7.5. Again, I think surface obs may have supported a little stronger for Japan landfall than JTWC went with. I'd probably go 95 kt or maybe even 100 kt instead of 85 kt.

I like the double 155 kt peak for Mangkhut, but the peaks are not where I would have had them (18Z September 11th and 18Z September 14th). Looked like it was clearly intenifying up to Luzon landfall too, not weakening to 140 kt.

The 18Z October 1st bump up from 135 kt to 150 kt for Kong-rey was perhaps the most needed edit I've seen. I'd argue that 155 kt or perhaps even 160 kt would have been more representative of true intensity given the extremely obvious T 7.5 and high microwave intensity estimates, but the original 135 kt at that point was perhaps my biggest gripe of the entire season...

...Until I saw what they did with the Yutu (first) peak intensity. A bump down to 150 kt? Really?? What is the basis for that??? How can you justify that move with perhaps the most obvious T 7.5 signature you'll ever see? Not to mention an almost 23ºC eye temp and an almost 104ºC eye/CDO temperature differential, which ranks only behind Haiyan and Nida! I think a 160 kt change is way easier to argue than a 150 kt drop. Yutu got a second 150 kt peak (which is probably fine) but that first change has me miffed.

[1900hurricane]

Not actually 155 kt, just "150 kt"...

[1900hurricane]

Anyway, here's my updated numbers.

[NotoSans]

JTWC's 150kt for Yutu's first peak is perhaps based on the assessment by NWS Guam (See: https://www.guampdn.com/story/news/2018 ... 370695002/), and second peak is based heavily on SATCON.

[euro6208]

I'm bummed by the decrease in intensity for Yutu. It looked mighty impressive and worthy of a 7.5. Peak sustained winds in cat 5's are not always observed due to instruments being damaged and of course human life is precious. No one wants to get killed documenting these storms!

Can't also believe the 3 known typhoon chasers never thought of intercepting this one! Would have been valuable data.

[SconnieCane]

I'm bummed by the decrease in intensity for Yutu. It looked mighty impressive and worthy of a 7.5. Peak sustained winds in cat 5's are not always observed due to instruments being damaged and of course human life is precious. No one wants to get killed documenting these storms!

Can't also believe the 3 known typhoon chasers never thought of intercepting this one! Would have been valuable data.

Josh M. (iCyclone) did intercept it, but in the Philippines, not for its Cat. 5 landfall in the Marianas.

[1900hurricane]

JTWC's 150kt for Yutu's first peak is perhaps based on the assessment by NWS Guam (See: https://www.guampdn.com/story/news/2018 ... 370695002/), and second peak is based heavily on SATCON.

Maybe, it is possible I guess. I don't know though, JTWC ignored such data for Soudelor '15, keeping the operational 90 kt instead of the 115 kt suggested by a similar assessment following that one. They also seemed not to really factor in surface data with Maria and Jebi, so why the sudden shift with Yutu? And even with the 150 kt assessment, I don't think it should disqualify a 155 kt or even 160 kt intensity at 12Z October 24th. Most eyewall locations in Tinian and Saipan probably easily saw category 5 conditions, but the Vmax may have been confined to the extreme southern portion of Saipan or extreme northern Tinian, or perhaps even stayed in the channel just between the islands.

[1900hurricane]

I make mock best tracks for Maria and Mangkhut prior to best track being released. Here's how final best track compares to operational best track as well as my thoughts for the two systems, in graphical format. I'm generally pleased with Maria at the two intensity peaks and especially between them. That was some of JTWC's best changes in my opinion, and the between peak period is actually almost identical to my mock best track.

Peak Mangkhut is actually closer to my mock than I originally thought, but I still think JTWC whiffed on the initial peak and period leading up to it (160 kt vs 140 kt by JTWC with very strong SATCON support) and the Luzon landfall (I strengthened up to 155 kt based on IR, microwave, and surface estimates while JTWC weakened to 140 kt). JTWC also went down a little near Hong Kong landfall while I went up.

[1900hurricane]

 https://twitter.com/1900hurricane/status/1179459850083815425

[euro6208]

Shocking too that Yutu was the only one downgraded in intensity. Probrably the best looking in 2018 globally.

[1900hurricane]

Yutu isn't the only one to get a drop, but it is certainly the highest profile. Jongdari and Shanshan also saw 5 kt drops. Despite the peak drop, Yutu actually saw a huge increase in ACE and other stats due to higher estimated intensity later on.

[404UserNotFound]

Oh hey, the 2018 Annual Tropical Cyclone Report is finally out...in 2020. Wonder what took them so long?