WPAC: GAEMI - Post-Tropical

[Hayabusa]

Latest 06Z synop from science garden (98430) has 207 mm accumulated rainfall for the past 6 hours since 00Z.

SMPH01 RPSG 240600
AAXX 24061
98430 11410 83202 10242 20237 39995 40044 58006 62071 79596 8392/ 333 56599 81715 82918 88457 94940 90410 91109 91534= JB

[doomhaMwx]

Buoy obs + radar velocities support supertyphoon intensity.

 https://x.com/doomhaMwx/status/1816033252274213269



 https://x.com/CyanideCN_/status/1815940064624730124

[mrbagyo]

strongest gust ive seen so far is 45.7 m/s at Heping station in Hualien county

[Hurricane2022]

????
 https://x.com/ak_1515/status/1816050341646901627

[R o x]

The mountains keep it at bay at 30 km of the coast moving more and more south
https://www.cwa.gov.tw/V8/E/W/OBS_Radar.html

[cycloneye]

 https://x.com/zoom_earth/status/1816080785251660168

[Hurricane2022]

 https://x.com/VortixWx/status/1816082194227396856

[kevin]

An overview of surface observations and analyses:
*Weather data = https://meteologix.com/
*Sea/land conversion factors for 10-min/1-min/gusts = https://www.researchgate.net/figure/Draft-Recommended-10m-Conversion-Factors_tbl1_237826652
*Altitude correction = https://www.nhc.noaa.gov/aboutwindprofile.shtml

Conclusion (see observations and analyses further down for details)

Note that none of the surface measurements listened below entered the eye or even the inner eyewall and still measured hurricane-force winds and adjusted gusts well over 100 kt. Based on satellite presentation and a blend of the radar analyses combined with the high confidence of the MW sounder I'd go with the lower range of the latter estimate -> 140 kt. Using the KZC analyses for this value (remaining inputs taken from JMA) results in a pressure estimate of 893 mb (input: 140 kt, 23.7N, 10 kt translation speed, 323 nm TS winds, 998 mb environmental pressure). Based on these analyses I'd conclude that Gaemi's official peak intensity is significantly underestimated and is closer to 893 mb / 140 kt than the current 940 mb / 125 kt. Even if Gaemi's wind speed is 125 kt, the storm's latitude, translational speed and especially its anomalously large gale radius would still result in a very low pressure of 909 mb instead of 940 mb.

Surface observations

Sustained winds

Yonagunijima Island (30m)
07:00AM CEST
10-min average wind speed = 122 kmh / 66 kt
-> Converts to 132 kmh / 71 kt for 1-minute sea-level winds (1.16 factor for 1-minute & 1/1.07 factor for altitude correction)
https://meteologix.com/nl/observations/1220-e-213-n/wind-average-10min/20240724-0500z.html#obs-detail-TA1280

Lan Yu (325m)
11:00AM CEST
10-min average wind speed = 163 kmh / 88 kt
-> Converts to 144 kmh / 78 kt for 1-minute sea-level winds (1.16 factor for 1-minute & 1/1.31 factor for altitude correction)
https://meteologix.com/nl/observations/1220-e-213-n/wind-average-10min/20240724-0600z.html#obs-detail-595670

Pengjia Yu (102m)
11:00AM CEST
10-min average wind speed = 133 kmh / 72 kt
-> Converts to 130 kmh / 70 kt for 1-minute sea-level winds (1.16 factor for 1-minute & 1/1.19 factor for altitude correction)
https://meteologix.com/nl/observations/1220-e-213-n/wind-average-10min/20240724-0900z.html#obs-detail-589740

Gusts

Yonagunijima Island (30m)
07:00AM CEST
Maximum 10-minute gust = 181 kmh / 98 kt
-> Converts to 230 kmh / 124 kt for instantaneous sea-level gusts (1.36 factor for 1-minute & 1/1.07 factor for altitude correction)
https://meteologix.com/nl/observations/1220-e-213-n/gusts-10min/20240724-0500z.html#obs-detail-TA1280

Tokorono (15m)
06:30AM CEST
Maximum 10-minute gust = 165 kmh / 89 kt
-> Converts to 218 kmh / 118 kt for instantaneous sea-level gusts (1.36 factor for 1-minute & 1/1.03 factor for altitude correction)
https://meteologix.com/nl/observations/1220-e-213-n/gusts-10min/20240724-0500z.html#obs-detail-TA1280

Yonaguni Airport (19m)
06:23AM CEST
Maximum 10-minute gust = 165 kmh / 89 kt
-> Converts to 218 kmh / 118 kt for instantaneous sea-level gusts (1.36 factor for 1-minute & 1/1.03 factor for altitude correction)
https://meteologix.com/nl/observations/1220-e-213-n/gusts-10min/20240724-0500z.html#obs-detail-TA1280

Sea-level air pressure QFF

Yonagunijima Island (30m)
06:40AM CEST
Mininum sea-level pressure = 967.4 mb
https://meteologix.com/nl/observations/1220-e-213-n/pressure-qff/20240724-0700z.html#obs-detail-TA1280

Other analyses at peak intensity
Source = https://tropic.ssec.wisc.edu/real-time/summary/summary.05W_2024.html

ADT
927 mb / 115 kt at 05:30z
2024JUL24 053000 6.0 927.2 115.0 5.9 6.0 6.0 NO LIMIT ON OFF OFF OFF -23.86 -73.28 EYE -99 IR 61.0 24.10 -122.54 ARCHER HIM-9 34.7

AiDT
114 kt at 07:00z
20240724 070000 115 114 125

D-PRINT
923 mb / 125 kt at 09:00z
20240724 0900 UTC 923 hPa 125 kts 118 kts 132 kts

DMINT
930 mb / 128 kt at 05:12z
20240724 0512 UTC AMSR2 930 hPa 128 kts 121 kts 135 kts

MW Sounders (CIMSS AMSU)
896 mb / 152 kt at 02:58z

| Estimated MSLP: 896 hPa
| Estimated Maximum Sustained Wind: 152 kts
| Estimate Confidence: Good ( +/- 10mb +/- 12kts )
-----------------------------------------------------------------
Storm is sub-sampled: Bias correction applied is -10.7 hPa

SATCON
911 mb / 137 kt at 05:30z
2024 WP 05 206.229 2024JUL24 053000 24.10 -122.54 2 911 137

ATMS
910 mb / 133 kt at 07:24z

SSMIS
910 mb / 133 kt at 07:24z

CIRA ATMS
948 mb / 101 kt at 07:24z

[1900hurricane]

I have tracked many TCs. From start to finish, Gaemi has been a weird one. I have not gotten many opportunities to post because I’ve been so busy with my own meteorology job, but I’ve definitely been watching closely.

[MarioProtVI]

Gaemi makes the EPac look even more pathetic if the analysis is right. Imagine the Atlantic and WPac having their first Cat 5s by the end of July while the EPac doesn’t even have its second named storm or first Hurricane yet still. Amazing.

[NotoSans]

 https://twitter.com/squirtleinhk/status/1816152199355080870

[qscdefb]

Gaemi is a very large storm, and the pressure drop before arriving at the eyewall is significant: the floating buoy registering 949hPa is roughly at r=2*RMW, and has a pressure 50hPa below the (already low) background pressure.
Provided that the maximum radar velocities hold up, the inner core above the boundary layer has an intensity perhaps on par with Rita/Irma, and would allow for another drop of 70hPa from twice the RMW to the center.

[kevin]

JMA lists 30 kt radii instead of 34 kt, so the JMA radii listed are going to be larger. I ended up creating a conversion factor by correlating the JMA and JTWC radii at the same time, but it breaks down for older systems before at least Quickscat in 1999, which almost always have listed JMA radii which must be way too large. It would be nice to have an apples to apples comparison, but that really isn't possible using that data.

I now used a conversion factor of 0.65 from JMA R30 to normalize to NOAA R34 based on the results of this paper based on 1913 storms: https://link.springer.com/article/10.1007/s13143-022-00274-5. This conversion factor results in a lower gale radius of 210 nm instead of 323 nm and as such a less intense peak pressure of 901 mb / 140 kt instead of 893 mb. This is also much more in-line with SSHWS/JTWC's estimate of 919 mb / 125 kt, since the 210 nm gale radius would result in a pressure of 917 mb if I use 125 kt as the input instead of 140 kt.

[NotoSans]

 https://twitter.com/weather_models/status/1816811467854823611



An interpolation using 4km radar velocity also yields ~885mb pressure. But do note that derivations using radar velocities are very sensitive to fine details and have large margin of errors.

[1900hurricane]

It's not impossible, but I am skeptical, especially considering how far outside the RMW the nearest pressure readings are. My first thought given limited information would be around 900 mb or so, near where the deepest sounders were.