Super Typhoon Haiyan's Intensity

[Boris Konon]

This was posted on another forum:

"170 kts was the highest wind speed ever given to a typhoon by the JTWC. As the highest value in the
modern historical record, this has generated some controversy."

I thought the same thing when I saw 170 kt on the JTWC advisory. I couldn't recall anything higher
than 160 kt in an operational JTWC advisory the last 20 years. Keep in mind this 170 kt based solely
on satellite estimates.

I think the day before landfall when the eye of Haiyan just missed the island nation of Palau, it could have
been stronger. Why? The eye was about half the size it was the day it made landfall. It went through
an eyewall replacement cycle and the eye increased in diameter. That's a biggie. It's not about absolute
central pressure for the really extreme winds, it's about pressure gradient, and the smaller the
eye (pinhole eye we have heard many times), the lower the pressure and more intense sustained winds
in the inner core region. Two TCs can have the same exact central pressure, but if one does not have a
tight and compact inner core/small eye, the winds can be much weaker, 30-40 kt difference in
max sustained winds in some cases.

Here is the Haiyan IR loop the day before landfall.
http://home.comcast.net/~trwplusa/haiyanloop1.gif

And here it is the day of landfall, notice a difference in the eye size?
http://home.comcast.net/~trwplusa/haiyanloop2.gif

The CDO is more symmetric and larger the day of landfall, but the eye diameter is also larger.
The overall power of the storm may be the same or stronger with the larger eye, but again,
absolute extreme winds I think are more dependent on the tightness of the inner core than
overall power. Many ET storms have the power of Cat 3 hurricanes, but their max sustained
winds are not as high as a Cat 3 hurricane b/c the wind field is much more spread out.

Of note, trochoidal oscillations are evident with the eye in the first loop the day before landfall.
The pinhole eye of HU Wilma in Oct 2005 did the same thing when it peaked in (Atlantic) record
intensity for central pressure. Soon after, an EWRC occurred. Two days later you had a much
larger eye with the pressure up 47 mb and a decrease of 35 kt for max sustained winds. VIS
image comparison here:

http://home.comcast.net/~trwplusa/wilmaeyecompare.GIF

Granted, the eye diameter increase in Haiyan was not nearly as dramatic, but it does lend
credence that a decent rise of pressure and decrease of max sustained winds does
occur after an EWRC. I apologize if I am stating the obvious here, but sometime we can
overlook the obvious amidst intense speculation and thought!

So the question is, would a more symmetric, wider, and colder cloud top CDO compensate
and give winds as strong or stronger than a CDO a bit less organized but with an eye half
the size? Without in-situ data, there no way to really tell. However, as I pointed out above,
an eye diameter size could be more of a factor.

More factors -- vertical storm structure and efficiency of downward transport of momentum in the
boundary layer can significantly impact the winds at the surface. I realize this is more of a factor when
a TC gets out of the tropics, but even in the tropics, no two TCs or their surrounding environmental
conditions are exactly alike. This is one reason why Dvorak estimates is not always accurate
as to how intense the winds are in a TC. In recent years with GPS dropsondes and the SMFR, we have
found impressive IR satellite appearance and T numbers do not always equate to expected Dvorak
estimates of surface winds.

This may sound like splitting hairs, but when it comes to the absolute extremes (i.e. world records),
details like this are very important.

Thoughts?

Boris

 

[MClarkson]

That is the cyclostrophic wind balance equation. At larger radii you need less PGF, so eye size is not well correlated with wind speed (at least in theory). You can have cat 5 winds in both tiny and large eyes. I agree that in reality pinhole eyes typically have winds that are stronger than wide eyes, but I do not think this matters as much as posted. A large eye can still have its wind concentrated in its eyewall.

I don't have all the data yet but at first glance (from the chasers in Tacloban and Tacloban/Guiuan airports before they failed) it looks like the inner core was rather compact, with fairly weak winds until the eyewall itself. The symmetry and cloud tops were so much better in the most recent image that I would say it is likely that wind speed was highest when satellite presentation was best (just about as its right side eyewall scraped land near Guiuan). The only thing about the storm at that point that was not epic was its radar presentation, but I cannot say for sure whether this was an artifact of precip shading or range from the radar station in Cebu or a real weakness in the northern eyewall. Given the best-ever satellite presentation, I would lean towards radar limitations rather than any problem with the eyewall itself.

I don't know if some other storm that was nearly as powerful but more compact could have edged out this storm for absolute highest wind. We just don't have the measurements for specific statements like that. I think the most accurate statement is something like "Haiyan is the favorite for lowest central pressure and a contender for highest wind speed"

 

[Boris Konon]

That is the cyclostrophic wind balance equation. At larger radii you need less PGF, so eye size is not well correlated with wind speed (at least in theory). You can have cat 5 winds in both tiny and large eyes. I agree that in reality pinhole eyes typically have winds that are stronger than wide eyes, but I do not think this matters as much as posted. A large eye can still have its wind concentrated in its eyewall.

I don't have all the data yet but at first glance (from the chasers in Tacloban and Tacloban/Guiuan airports before they failed) it looks like the inner core was rather compact, with fairly weak winds until the eyewall itself. The symmetry and cloud tops were so much better in the most recent image that I would say it is likely that wind speed was highest when satellite presentation was best (just about as its right side eyewall scraped land near Guiuan). The only thing about the storm at that point that was not epic was its radar presentation, but I cannot say for sure whether this was an artifact of precip shading or range from the radar station in Cebu or a real weakness in the northern eyewall. Given the best-ever satellite presentation, I would lean towards radar limitations rather than any problem with the eyewall itself.

I don't know if some other storm that was nearly as powerful but more compact could have edged out this storm for absolute highest wind. We just don't have the measurements for specific statements like that. I think the most accurate statement is something like "Haiyan is the favorite for lowest central pressure and a contender for highest wind speed"

Good information on eye size and wind relationship. I didn't realize it was more complicated than the simple, "less eye diameter, more intense the winds"

The statement about Haiyan for the record books as to most intense I agree with. Certainly safe to say it is among the top five most intense TCs ever observed.