Maximum "Sustained" Winds?

[cdcollura]

Good day all,

I am open to any input or corrections on this...

I seen the chases done on Typhoon "Krasa" in Taiwan and seen the maximum winds "lighter" than what was expected by us "western" storm chasers.

I understand that the 1-minute (60 second) mean wind speed is used to measure tropical cyclone winds according to the US (NHC / NWS) where a 10 m height is preferred in a marine environment (open sea area, marine exposure - such as an onshore eyewall flow off the ocean).

What determines the "gust" speeds? Do they use the 10-second mean / peak gust?

I see many reports saying maximum sustained at 120 MPH with "gusts" to 145 - Is that 145 for 10s or what about 3s?

I am also under the impression that typhoons, measured by JTWC / Japan use the 10-second sustained wind and not the 60 second (1 minute) rule like we do?

Is this why Krasa had "130 MPH winds" and those in Taiwan only felt 100+ MPH? Were these 130 MPH for 10s and not 1 minute? Just curious.

Or maybe the little loop it did just off the island upwelled cooler water causing Krasa's convection to crap-out and it simply weakened?

In comparison, the new EF scale uses a 3-second gust rule, making good sense for tornadoes, with an overlay of damage observed.

In comparison, a hurricane like Andrew back in 1992 with 165-MPH sustained winds gusting to over 200 (10 s) ... In 3 seconds a cat-5 hurricane like that is like an EF-5 tornado 10-20 miles wide? LOL!!

 

[IAN GIAMMANCO]

I would assume in Japan they use the WMO standard for sustained wind speed which is actually a 10-minute mean wind, I am not sure what JTWC uses as their sustained wind value. I am guessing the gust is still a 3-second gust which is used in most engineering applications for minimum design standards but I could be wrong there. The advisory maximum gusts values are probably computed from a gust factor applied to the mean wind speed given open terrain exposure.

 

[Jim Leonard]

JTWC uses the one minute average, all other agencies in the western and south pacific use the 10 minute average on sustained winds.

 

[Josh Morgerman]

My understanding:

Re: sustained winds... The USA uses a 1-min average to express a sustained wind, whereas most other agencies throughout the world use a 10-min average-- including Japan's JMA and Australia's BoM. Therefore, the JTWC (an American agency) uses a 1-min average (as Jim mentions above).

The factor for converting a 10-min wind to a 1-min wind is 1.12 to 1.15, depending on who you talk to. (Australia's BoM recommends 1.15, and that's what I use.) Of course, this factor won't yield precise values-- but it's helpful for making rough comparisons.

Re: gusts... I believe most world agencies-- including the USA-- use a 3-second extreme value.