EPAC Tropical Action 2011

[battlebrick]

after seeing those loops I am very convinced that Hilary got to cat-5 strength.

[HurricaneJosh]

after seeing those loops I am very convinced that Hilary got to cat-5 strength.

Based on what? It looks to me like what it was-- a solid Cat 4.

As awesome as it looked, usually Cat 5s sustain a perfectly symmetric ring of the heaviest (dark grey) convection around the eye. Hilary did not do this. The NHC's estimate-- 125 kt-- sounds right to me. That is a very powerful hurricane, and a closeup, high-res visible loop of its core should be pure awesomeness.

[HurricaneJosh]

The 8 pm PDT advisory has Hilary slightly weaker, but it's still a Cat 4: 950 mb/115 kt. The models have trended W, so that a Baja landfall no longer looks as likely.

EDIT: The new advisory intensity is not weaker, but actually the same as 2 pm PDT. Oops!

[battlebrick]

Based on what? It looks to me like what it was-- a solid Cat 4.

As awesome as it looked, usually Cat 5s sustain a perfectly symmetric ring of the heaviest (dark grey) convection around the eye. Hilary did not do this. The NHC's estimate-- 125 kt-- sounds right to me. That is a very powerful hurricane, and a closeup, high-res visible loop of its core should be pure awesomeness.

What did Dora have that Hilary didn't?

[HurricaneJosh]

What did Dora have that Hilary didn't?

Nothing much, since Dora was also a Cat 4. (At its peak, Dora's winds were only 10 kt higher than Hilary's-- 135 kt.)

[battlebrick]

Nothing much, since Dora was also a Cat 4. (At its peak, Dora's winds were only 10 kt higher than Hilary's-- 135 kt.)

Well, I do think Hilary looked better than Dora at it's peak.

Pinhole eye with -80c cloud tops surrounding:

[HurricaneJosh]

Well, I do think Hilary looked better than Dora at it's peak.

Pinhole eye with -80c cloud tops surrounding:

I think it looked beyond awesome, but I don't remember those dark greys sustaining in a perfect circle for that long. The dudes at the NHC are experts at interpreting satellite imagery, and I feel cool with their estimate. Personally, I thought they were going to go a little higher when it was looking like that-- maybe 130 kt-- but I'ms sure they had their reasons.

[phil882]

Based on what? It looks to me like what it was-- a solid Cat 4.

As awesome as it looked, usually Cat 5s sustain a perfectly symmetric ring of the heaviest (dark grey) convection around the eye. Hilary did not do this. The NHC's estimate-- 125 kt-- sounds right to me. That is a very powerful hurricane, and a closeup, high-res visible loop of its core should be pure awesomeness.

I'm actually going to disagree with you. While you are right that the some intense Category 5 hurricanes have a ring of <-80C convection around the eye (the dark grey equivalent on the NHC enhanced IR), there are plenty of examples of Cat5 hurricanes that only maxed out at around -75C.

Some recent examples are Celia 2010, Felix 2007, Emily 2005, Katrina 2005... the list goes on. The reason why Hilary never made it to cat five using satellite estimates was that the eye was not warm enough in the center (it never cleared out 100%). However, satellite estimates typically have a lot higher of an error bar when you investigate small tropical cyclones such as Hilary. This is why it would have been great to get some reconnaissance missions in to investigate the system further and find out the "true" intensity.

The 8 pm PDT advisory has Hilary slightly weaker, but it's still a Cat 4: 950 mb/115 kt. The models have trended W, so that a Baja landfall no longer looks as likely.

It was 115 knots at 2pm. In fact that dropped the pressure a mb at 8pm, but we are splitting hairs here

[HurricaneJosh]

I'm actually going to disagree with you. While you are right that the some intense Category 5 hurricanes have a ring of <-80C convection around the eye (the dark grey equivalent on the NHC enhanced IR), there are plenty of examples of Cat5 hurricanes that only maxed out at around -75C.

Some recent examples are Celia 2010, Felix 2007, Emily 2005, Katrina 2005... the list goes on. The reason why Hilary never made it to cat five using satellite estimates was that the eye was not warm enough in the center (it never cleared out 100%). However, satellite estimates typically have a lot higher of an error bar when you investigate small tropical cyclones such as Hilary. This is why it would have been great to get some reconnaissance missions in to investigate the system further and find out the "true" intensity.

I said "usually". We usually see that with Cat-5 classification.

Back to the original point... Battlebrick said he was convinced it was a Cat 5 based on a really sexy, high-res visible loop. I don't see how he came to that conclusion from those loops, and I am cool with the NHC's verdict. If you agree with battlebrick, then please share what about the visible loop says "Cat 5" to you.

It was 115 knots at 2pm, but we are splitting hairs here

You get a gold star, dude!1!

[phil882]

I said "usually". We usually see that with Cat-5 classification.

Back to the original point... Battlebrick said he was convinced it was a Cat 5 based on a really sexy, high-res visible loop. I don't see how he came to that conclusion from those loops, and I am cool with the NHC's verdict. If you agree with battlebrick, then please share what about the visible loop says "Cat 5" to you.

I guess I should clarify. I stated that based on satellite classification alone, you couldn't classify this anything other than a cat 4 storm. However, I'm disagreeing with you that a ring of -80C minus temperatures is what you usually witness with regards to Category 5 formation. What is more important is the difference between how warm the eye is compared to how cold the convection surrounding the eye is. Its these two factors in combination that really tell the tale on how strong a tropical cyclone is based on satellite estimates. You can have warmer cloud top convective temperatures surrounding an eye if the eye is ridiculously warm. My thoughts are that Hilary could have easily been classified as a category 5 with the minimum cloud top temperatures experienced during its peak intensity. However, the eye was still a bit too cool allow Dvorak estimates to reach category 5 intensity.

The problem though with really small TCs is that the eye size becomes sufficiently small that IR alone might not be able to sample the warmest cloud top temperatures within the eye. Keep in mind both IR and WV imagery only have a resolution of 4km. As an eye approaches that size the number of pixels that can represent an eye also decrease. My understanding is that Dvorak was designed for an average sized tropical cyclone, so when a storm becomes so small that the pinhole eye can be properly resolved on satellite, then you will see a significant increase your intensity error with Dvorak estimates.

[HurricaneJosh]

I guess I should clarify. I stated that based on satellite classification alone, you couldn't classify this anything other than a cat 4 storm. However, I'm disagreeing with you that a ring of -80C minus temperatures is what you usually witness with regards to Category 5 formation. What is more important is the difference between how warm the eye is compared to how cold the convection surrounding the eye is. Its these two factors in combination that really tell the tale on how strong a tropical cyclone is based on satellite estimates. You can have warmer cloud top convective temperatures surrounding an eye if the eye is ridiculously warm. My thoughts are that Hilary could have easily been classified as a category 5 with the minimum cloud top temperatures experienced during its peak intensity. However, the eye was still a bit too cool allow Dvorak estimates to reach category 5 intensity.

The problem though with really small TCs is that the eye size becomes sufficiently small that IR alone might not be able to sample the warmest cloud top temperatures within the eye. Keep in mind both IR and WV imagery only have a resolution of 4km. As an eye approaches that size the number of pixels that can represent an eye also decrease. My understanding is that Dvorak was designed for an average sized tropical cyclone, so when a storm becomes so small that the pinhole eye can be properly resolved on satellite, then you will see a significant increase your intensity error with Dvorak estimates.

We might be talking past each other. I'm not suggesting that "symmetric ring of dark greys sustained for 6 hr" is a technical requirement to estimate winds at 140 kt-- I was just saying that's something I generally expect to see with Cat 5s. I wasn't intending it as a technical criterion. I agree that there are many other criteria.

Back to the original point, I don't know how Cat-5 intensity was gleaned from a visible loop. The NHC's call on this seemed reasonable to me.

I agree that the IR imagery often doesn't have the resolution to reveal the fine structural details of microcanes, with Charley 2004 being a good example-- it just didn't look that amazing on IR.

[phil882]

We might be talking past each other. I'm not suggesting that "symmetric ring of dark greys sustained for 6 hr" is a technical requirement to estimate winds at 140 kt-- I was just saying that's something I generally expect to see with Cat 5s. I wasn't intending it as a technical criterion. I agree that there are many other criteria.

Back to the original point, I don't know how Cat-5 intensity was gleaned from a visible loop. The NHC's call on this seemed reasonable to me.

I agree that the IR imagery often doesn't have the resolution to reveal the fine structural details of microcanes, with Charley 2004 being a good example-- it just didn't look that amazing on IR.

No you are right about visible... its a great tool to use to see structural chances with a system, as well as inner core features such as mesovorticies around and eyewall. However, their forecasting usefulness is normally limited to developing systems and weaker hurricanes. Once you see a system turn into a major hurricane, you expect a textbook visible satellite appearance and it becomes more difficult to infer the actual intensity of a system using visible imagery alone.

[HurricaneJosh]

No you are right about visible... its a great tool to use to see structural chances with a system, as well as inner core features such as mesovorticies around and eyewall. However, their forecasting usefulness is normally limited to developing systems and weaker hurricanes. Once you see a system turn into a major hurricane, you expect a textbook visible satellite appearance and it becomes more difficult to infer the actual intensity of a system using visible imagery alone.

Bingo Re: visibles. It's funny how visible imagery is so critical to understanding the intensity of weaker systems and then essentially useless with mature 'canes.

Back to Cat 5s without very cold cloud tops, which would you say is the best example, and do you have an image handy? (I'm not asking to be a pain in the butt, I'm just curious to see.)

[phil882]

Bingo Re: visibles. It's funny how visible imagery is so critical to understanding the intensity of weaker systems and then essentially useless with mature 'canes.

Back to Cat 5s without very cold cloud tops, which would you say is the best example, and do you have an image handy? (I'm not asking to be a pain in the butt, I'm just curious to see.)

Ok here are some comparisons. It seems that the main thing that Hilary lacked was a perfectly clear eyewall on enhanced IR.

Hilary (2011):

Celia (2010):

Felix (2007):

Emily (2005):

Katrina (2005):

[HurricaneJosh]

Thanks, Phil. And Jorge just pointed out perhaps the very best example of all. I was kind of embarrassed, because it's one I was actually in!

Jorge? Please post it. Drumroll...

My azz got handed to me tonight.

[wxmx]

Bingo Re: visibles. It's funny how visible imagery is so critical to understanding the intensity of weaker systems and then essentially useless with mature 'canes.

Back to Cat 5s without very cold cloud tops, which would you say is the best example, and do you have an image handy? (I'm not asking to be a pain in the butt, I'm just curious to see.)

One good example. I'm amazed that is the one you were actuall in and you forgot it!!

[HurricaneJosh]

So... If the coldness of the surrounding cloud tops were such an important criterion for Cat-5 status, and Dean had winds of 150 kt, then Hilary's winds must have been 180 kt.

Ugh.

I was wrong, I think, to suggest the closed circle of dark greys is even a broad indicator. Sorry, guys.

[phil882]

One good example. I'm amazed that is the one you were actuall in and you forgot it!!

To Josh's credit... it actually had a fair bit of colder cloud tops before landfall.

[HurricaneJosh]

To Josh's credit... it actually had a fair bit of colder cloud tops before landfall.

Thanks, but it was pretty-much peaking then. Peak intensity (905 mb/150 kt) was reached as it crossed the coast, so those darks should have been there if I was right. (Well, I guess the eye is a tad inland...)

[phil882]

Thanks, but it was pretty-much peaking then. Peak intensity (905 mb/150 kt) was reached as it crossed the coast, so those darks should have been there if I was right. Grrrrr.

Its all good. In reality we are really arguing over pretty minute details on satellite imagery. One of the main reasons why I mentioned the warmness of the eye also being is a big factor in Dvorak estimates is that traditionally enhanced IR has a much more muted color scale once temperatures increase beyond -30C. So what really seem like small changes in the enhanced IR scale of the eye are really much larger temperature variations. The differences between a white pixel and a grey pixel are quite great (~50-60C) while the difference between a red pixel and a yellow pixel are much smaller (~10C).

[HurricaneJosh]

Its all good. In reality we are really arguing over pretty minute details on satellite imagery. One of the main reasons why I mentioned the warmness of the eye also being is a big factor in Dvorak estimates is that traditionally enhanced IR has a much more muted color scale once temperatures increase beyond -30C. So what really seem like small changes in the enhanced IR scale of the eye are really much larger temperature variations. The differences between a white pixel and a grey pixel are quite great!

Interesting. Never thought about that before...

[wxmx]

To Josh's credit... it actually had a fair bit of colder cloud tops before landfall.

Not that colder... almost no yellow pixels

[HurricaneJosh]

Not that colder... almost no yellow pixels

Wow-- what a pussycane!

[tmagan]

I like Avila's headlines, like: 'Nothing new...' basically saying look to other storms for anything interesting.

[HurricaneJosh]

For such a small cyclone, Hilary is surprisingly durable. It's still going strong and looking healthy and symmetric this afternoon. Outflow looks maybe a tad restricted to the W, but the core is solid. Latest intensity is 953 mb/110 kt:

[apm]

Well, one point is that it is not such a small storm any more. It has completed the ERC and has re-intensified some this afternoon in addition to expanding considerably.

For such a small cyclone, Hilary is surprisingly durable. It's still going strong and looking healthy and symmetric this afternoon. Outflow looks maybe a tad restricted to the W, but the core is solid. Latest intensity is 953 mb/110 kt:

[HurricaneJosh]

Well, one point is that it is not such a small storm any more. It has completed the ERC and has re-intensified some this afternoon in addition to expanding considerably.

Actually, it's still quite small. In fact, the wind radii are the same or smaller than they were at peak intensity. The current estimated 64-kt radius is 25 nmi and the 34-kt radius is a tiny 60 nmi.

[apm]

There's no way that is still correct. The eye itself is nearly 25 miles across. And I'll bet there are TS force winds in those newly developed inner bands. Have you seen the latest images?

Actually, it's still quite small. In fact, the wind radii are the same or smaller than they were at peak intensity. The current estimated 64-kt radius is 25 nmi and the 34-kt radius is a tiny 60 nmi.

[HurricaneJosh]

There's no way that is still correct. The eye itself is nearly 25 miles across. And I'll bet there are TS force winds in those newly developed inner bands. Have you seen the latest images?

It still looks like a small system to me. Even if the eye is bigger, that isn't proof that the wind field is bigger. Anyhoo, I would need specific data beyond eyeballing some IR imagery to just say the NHC is flat-out wrong.

[wxmx]

Red isobarbs are below TS force (brown and purple are >35kts)...it's a dated ASCAT image (23 hours old), but it certainly looks pretty small