Cyclone Yasi

[HurricaneJosh]

So... How strong was Cyclone Yasi at landfall?

As I mentioned above, damage seems heaviest in towns that were right at or just left of the center: Mission Beach (the landfall point - light-purple-A), Tully (a tad SW of Mission Beach, in the path of the center - red), Cardwell (on the coast, ~25 mi S of the track - orange), and Mourilyan (just S of Innisfail, a tad N of the center - dark-purple).

The pics in the Brisbane Times show what I would call extensive but not catastrophic wind damage. For example, even in Mission Beach and Tully, a lot of the homes and buildings look OK. In fact, overall Cardwell looks harder-hit to me, as some of the aerial shots show multiple unroofed houses, and a lot of the trees have that stripped, wintry look-- another indicator of very high windspeeds. This all suggests that Cardwell got raked pretty good. (Despite this, notice that the big, fancy homes in the marina, right on the waterfront, look unscathed.)

I'm generally not seeing what we saw, for example, after Andrew 1992 in the suburbs S of Miami-- like, a complete mowing down of all residences. Given this, I would say it most certainly wasn't a Cat 5 on the USA scale (as has been suggested here), and that Cat 4 seems more reasonable.

Let's see what else we can find in terms of evidence on the ground. These are just initial impressions.

[EastCoastLow]

I'm really looking forward to seeing where this one recurves and recrosses the coast at. It's a big storm still and is moving quite a way inland. Sydney got the remnants of a tropical storm in the early 70's and the rain event was devastating.

I'm surprised at the photos above, damage is not quite as bad as I expected, however, that wasn't a low lying area.

[HurricaneJosh]

I'm really looking forward to seeing where this one recurves and recrosses the coast at. It's a big storm still and is moving quite a way inland. Sydney got the remnants of a tropical storm in the early 70's and the rain event was devastating.

I'm surprised at the photos above, damage is not quite as bad as I expected, however, that wasn't a low lying area.

That's my feeling as well-- I expected those towns to be completely flattened. Since I'm estimating the intensity based on windspeed, I'm personally interested in imagery of areas that were not inundated by the surge-- so that the effects of the winds alone can be easily separated from the effects of water.

I am going to do some more hunting around, to see what else we can find. I think there's still more evidence to collect!

[Normandy]

That's my feeling as well-- I expected those towns to be completely flattened. Since I'm estimating the intensity based on windspeed, I'm personally interested in imagery of areas that were not inundated by the surge-- so that the effects of the winds alone can be easily separated from the effects of water.

I am going to do some more hunting around, to see what else we can find. I think there's still more evidence to collect!

Unless surge is the culprit wind won't flatten whole towns. Andrew i feel was an exception because most of the pictures you see of "total devastation" were of mobile home parks.

[HurricaneJosh]

Unless surge is the culprit wind won't flatten whole towns. Andrew i feel was an exception because most of the pictures you see of "total devastation" were of mobile home parks.

The Andrew damage I am referring to was to standard subdivisions of ranch houses.

To clarify, by "flattened" I don't mean literally not a stick left standing-- of course that only happens in EF5 tornadoes-- but what I do mean is massive, widespread damage not only to roofs but to walls as well, with many partial structural failures.

Getting back to Yasi, I haven't seen any photos yet which show this kind of damage.

P.S. Wind has been the culprit behind spectacular and widespread hurricane/cyclone devastation-- not only Andrew 1992, but also Charley 2004, Celia 1970, and of course Cyclone Tracy 1974, which practically destroyed a city entirely with its winds.

[HurricaneJosh]

And finally, almost 24 hrs after landfall, Yasi is no longer a tropical cyclone.

It took a very un-Aussie track-- essentially a clean, straight line for several days:

[jconsor]

More damage pics:

http://www.theage.co...0201-1acgp.html

A station in Clump Point, very near the landfall location, reported a minimum pressure of 930 mb.

Also, some historical perspective from Jeff Masters' blog:

According to an email I received from Blair Trewin of the Australian Bureau of Meteorology, ”Yasi is almost certainly the most intense landfall in Queensland since at least 1918, and possibly since 1899. In 1918 there were two cyclones (at Mackay and Innisfail) with measured pressures in the upper 920s/low 930s but it is quite plausible that the minimum central pressures were lower than that. The 1899 (Mahina/Bathurst Bay) cyclone had a measured pressure (ship near shore) of 914 mb.

[A-L-E-X]

The Andrew damage I am referring to was to standard subdivisions of ranch houses.

To clarify, by "flattened" I don't mean literally not a stick left standing-- of course that only happens in EF5 tornadoes-- but what I do mean is massive, widespread damage not only to roofs but to walls as well, with many partial structural failures.

Getting back to Yasi, I haven't seen any photos yet which show this kind of damage.

P.S. Wind has been the culprit behind spectacular and widespread hurricane/cyclone devastation-- not only Andrew 1992, but also Charley 2004, Celia 1970, and of course Cyclone Tracy 1974, which practically destroyed a city entirely with its winds.

Josh, I've heard Andrew described as a very large tornado because of how compact it's eye was.... same with Charley. Perhaps a smaller more compact eye contributes to a higher intensity of damage near the center?

[Normandy]

The Andrew damage I am referring to was to standard subdivisions of ranch houses.

To clarify, by "flattened" I don't mean literally not a stick left standing-- of course that only happens in EF5 tornadoes-- but what I do mean is massive, widespread damage not only to roofs but to walls as well, with many partial structural failures.

Getting back to Yasi, I haven't seen any photos yet which show this kind of damage.

P.S. Wind has been the culprit behind spectacular and widespread hurricane/cyclone devastation-- not only Andrew 1992, but also Charley 2004, Celia 1970, and of course Cyclone Tracy 1974, which practically destroyed a city entirely with its winds.

I see your clarification. Regardless for a structure to survive true Category 4 winds it has to be very strong (Re-inforced concrete or steel construction). Wood framed construction stands little chance in these situations. Looking at the damage though I think Yasi was definitely a Cat 4, not a Cat 5 at landfall. I don't see the Dean damage like Majahual in any of the photos.

[HurricaneJosh]

More damage pics:

http://www.theage.co...0201-1acgp.html

A station in Clump Point, very near the landfall location, reported a minimum pressure of 930 mb.

Also, some historical perspective from Jeff Masters' blog:

According to an email I received from Blair Trewin of the Australian Bureau of Meteorology, ”Yasi is almost certainly the most intense landfall in Queensland since at least 1918, and possibly since 1899. In 1918 there were two cyclones (at Mackay and Innisfail) with measured pressures in the upper 920s/low 930s but it is quite plausible that the minimum central pressures were lower than that. The 1899 (Mahina/Bathurst Bay) cyclone had a measured pressure (ship near shore) of 914 mb.

Omg, I'm so glad you posted this, as I was really wondering what the central pressure was at landfall. Since Clump Point is in Mission Beach, which is exactly where the center came ashore, I think it's safe to say that the 930 mb would be close to the minimum. Interestingly, it matches perfectly with the BoM's satellite-based estimate before and during landfall. Nice going, BoM!

Re: the damage pics... I went through all of them. My main conclusion is that Mission Beach, Tully, and Cardwell had the highest winds-- no surprise there. There's plenty of heavy structural damage at those locations. Other locations-- including Innisfail, Ingham, and Townsville-- apparently fared much better.

[wxmx]

I think the measured central pressure and wind damage pretty much validates a cat 4 (SS) landfall...probably between 115 and 125kts (1 min).

[HurricaneJosh]

I think the measured central pressure and wind damage pretty much validates a cat 4 (SS) landfall...probably between 115 and 125kts (1 min).

I agree with this assessment-- a low- or midrange Cat 4. I do not feel it was 130 or 135 kt (1-min).

For comparison purposes, the standard NATL wind/pressure relationship (Brown et al.) yields 130 kt for a steady-state cyclone with a pressure of 930 mb within a tropical latitude. For large systems with huge RMWs-- like Yasi-- you can "penalize" the windspeed by as much as 10 kt (Landsea et al.). Yasi's enormous size plus the fact that pressures in this basin are generally lower for the same windspeed lead me to believe that 120 kt might be a good landfall intensity estimate.

This is not to diss Yasi. It was a truly tremendous cyclone by any yardstick. Hugo 1989 was a large, 120-kt cyclone when it hit SC-- and no one has ever suggested that Hugo was anything less than a monster.

[am19psu]

Let me preface this by saying I have zero expertise in assessing damage. That said, a +16C eye temperature is extremely warm and we saw mesovortices on the radar at landfall. I think it was 125-140 kts (1-min) at landfall.

[HurricaneJosh]

Let me preface this by saying I have zero expertise in assessing damage. That said, a +16C eye temperature is extremely warm and we saw mesovortices on the radar at landfall. I think it was 125-140 kts (1-min) at landfall.

Well, I should clarify that I'm not technically qualified to assess damage, either. But I have a feel for it, having looked at enough aftermaths, and then there's the wind/pressure/size metrics which just don't seem to add up to 135 kt or higher.

By the way, did we really confirm those mesovortices? I mean, I know you had a suspicion, but that radar is awfully low-res for picking out such features.

[am19psu]

Well, I should clarify that I'm not technically qualified to assess damage, either. But I have a feel for it, having looked at enough aftermaths, and then there's the wind/pressure/size metrics which just don't seem to add up to 135 kt or higher.

By the way, did we really confirm those mesovortices? I mean, I know you had a suspicion, but that radar is awfully low-res for picking out such features.

Yeah, I trust your's and Jorge's damage assessments, but at the same time, have we seen the full sample of photos yet?

I also don't know what the P-W relationship is for Australia. This didn't come out of a monsoon trough, so is the Atlantic/E Pacific P-W relationship better?

I keep coming back to the +16C eye temperature, which is warm in any basin. For reference, STY Megi was around that temperature when it was T7.0 and aircraft from ITOP were in there verifying 155 kt winds.

I've not read any confirmation of the mesovortices. I'd imagine it will come from aircraft damage assessments, if we ever get them.

[Scott747]

I'm definitely with the group that has yet to see some solid photographic verification that Yasi was a legit five at landfall.

Of course as we know those winds were confined to a small area and we could yet see some better representation over the coming days.

Probably a good time to review the Mahahual images.

[am19psu]

I should probably point out, that I am not in the 5 camp. I'd go 130 or 135 kts based on Dvorak, SATCON, and the 929mb at Tully.

[HurricaneJosh]

Yeah, I trust your's and Jorge's damage assessments, but at the same time, have we seen the full sample of photos yet?

I also don't know what the P-W relationship is for Australia. This didn't come out of a monsoon trough, so is the Atlantic/E Pacific P-W relationship better?

I keep coming back to the +16C eye temperature, which is warm in any basin. For reference, STY Megi was around that temperature when it was T7.0 and aircraft from ITOP were in there verifying 155 kt winds.

I've not read any confirmation of the mesovortices. I'd imagine it will come from aircraft damage assessments, if we ever get them.

Thanks for the response, Adam. For sure, we need to see the full extent of the damage imagery, and I will be looking for more examples from Mission Beach, Tully, and Cardwell in the coming days.

I used the P/W relationship for the NATL, since I'm familiar with it-- and since I assume that the Aussie basin would yield a lower wind value for the same pressure. So, if the NATL P/W relationship yields 130 kt, I feel it's safe to assume the standard wind value would be lower for the same pressure in the SPAC-- especially with such a large system. But perhaps I'm oversimplifying all this. After all, no two cyclones are alike, and the P/W tables and attendant rules are only rough guides.

I see your point Re: the eye temp-- it is darn impressive-- but for me it doesn't take precedence over the pressure/wind/size metrics.

I'm definitely with the group that has yet to see some solid photographic verification that Yasi was a legit five at landfall.

Of course as we know those winds were confined to a small area and we could yet see some better representation over the coming days.

Probably a good time to review the Mahahual images.

Hey, Scott!

The Majahual images from Dean left me feeling a tad... unimpressed. I mean, the place looked beaten up, but I would expect the landfall point of a 150-kt cyclone to look like a nuke had landed there-- and it didn't quite look nuclear to me.

To clarify, official estimates from both the BoM and the JTWC make Yasi a Cat 4 (USA) at landfall. Neither of those agencies estimated it to be a 5.

[HurricaneJosh]

I should probably point out, that I am not in the 5 camp. I'd go 130 or 135 kts based on Dvorak, SATCON, and the 929mb at Tully.

Did Tully report 929 mb? The lowest I was aware of was 930 mb at Clump Point, which is nearby (in Mission Beach). Are we talking about the same station?

[am19psu]

I see your point Re: the eye temp-- it is darn impressive-- but for me it doesn't take precedence over the pressure/wind/size metrics.

The size bothers me, too. Its gale radius was larger than Katrina's. The reason why the eye temp takes precedence for me is that you need some insane updrafts to create that much subsidence in the eye and that can only happen if the pressure gradient in the eyewall is super strong. The eye temp is also why I think there were mesovorts in the eyewalls. Even though the radar was coarse, they almost had to be present to generate that much subsidence in the eye.

[am19psu]

Did Tully report 929 mb? The lowest I was aware of was 930 mb at Clump Point, which is nearby (in Mission Beach). Are we talking about the same station?

I don't know which station reported it, but it was confirmed by a forecaster with TCWC Brisbane.

[PSUBlizzicane2007]

Based on damage, trees, and pressure... this was very clearly a strong category 4 SS at landfall. Probably between 130-135 KT 1-min.

[Scott747]

Hey, Scott!

The Majahual images from Dean left me feeling a tad... unimpressed. I mean, the place looked beaten up, but I would expect the landfall point of a 150-kt cyclone to look like a nuke had landed there-- and it didn't quite look nuclear to me.

To clarify, official estimates from both the BoM and the JTWC make Yasi a Cat 4 (USA) at landfall. Neither of those agencies estimated it to be a 5.

Well as you know I tend to focus on the foilage and tree damage. There was a series of photos that were incredibly impressive from Mahahual that looked 'nuke' like and enough from a photographic representation to make it cat 5 worthy.

Yet to see anything comparable out of Yasi and why I mentioned reviewing some of the images.

[HurricaneJosh]

The size bothers me, too. Its gale radius was larger than Katrina's. The reason why the eye temp takes precedence for me is that you need some insane updrafts to create that much subsidence in the eye and that can only happen if the pressure gradient in the eyewall is super strong. The eye temp is also why I think there were mesovorts in the eyewalls. Even though the radar was coarse, they almost had to be present to generate that much subsidence in the eye.

Interesting. I didn't know all this about eye temperature. I mean, I knew it was an indicator of the system's potency, but I didn't realize it was to this degree. Ya learn something new everyday! Thanks for the info.

I don't know which station reported it, but it was confirmed by a forecaster with TCWC Brisbane.

OK, cool-- so we can take it as official? (P.S. Was it via eMail or is there a link somewhere? I'd like to find out more about the reading-- the time, etc.)

Based on damage, trees, and pressure... this was very clearly a strong category 4 SS at landfall. Probably between 130-135 KT 1-min.

Based on pressure? A cyclone of this size and this pressure in this basin wouldn't normally produce winds that high (see my post above), so I would say the pressure would not be used to support this wind estimate.

Re: the trees, lots are stripped, but not all-- it's not a complete strip job. Re: the damage, some of it looks impressive, but 135 kt? I'm not convinced. 135 kt is really extreme.

[HurricaneJosh]

Well as you know I tend to focus on the foilage and tree damage. There was a series of photos that were incredibly impressive from Mahahual that looked 'nuke' like and enough from a photographic representation to make it cat 5 worthy.

Ah, OK. Gotcha. Yeah, trees are a good indicator-- more reliable than buildings.

Yet to see anything comparable out of Yasi and why I mentioned reviewing some of the images.

Yep.

[aslkahuna]

A couple of points to make about wind/pressure relationships. First off with a La Niña, you are going to have pressures in SPAC somewhat higher than climo which brings up a second point. JTWC in their assessment of STY Paka when it passed Guam noted that when pressure are higher than climo in WPAC (or because of normally seasonal higher pressures) that the WPAC w/p relationship didn't work well and that the ATL w/r one was better under those conditions. This brings up Megi-the w/r relationship for JTWC for a storm with 890 mb pressure is around 140 kt yet Megi clearly had 155 kt (if not more as measured) so that particular w/p relationship may not really work out that well even in WPAC.

Steve

[HurricaneJosh]

A couple of points to make about wind/pressure relationships. First off with a La Niña, you are going to have pressures in SPAC somewhat higher than climo which brings up a second point. JTWC in their assessment of STY Paka when it passed Guam noted that when pressure are higher than climo in WPAC (or because of normally seasonal higher pressures) that the WPAC w/p relationship didn't work well and that the ATL w/r one was better under those conditions. This brings up Megi-the w/r relationship for JTWC for a storm with 890 mb pressure is around 140 kt yet Megi clearly had 155 kt (if not more as measured) so that particular w/p relationship may not really work out that well even in WPAC.

Steve

Hmmm-- interesting. So given the above, what are your thoughts Re: Yasi? Are you in the high-end Cat-4 camp-- or even higher?

I'm just having trouble imagining a steady-state, 929-mb cyclone of such enormous size producing winds of 135 kt.

[am19psu]

steady-state

Why steady-state? It had clearly intensified over the last six and twelve hours. From 614z to 1232z, the eye warmed from 9C to 16C, although the cloud tops remained the same -76ishC.

[HurricaneJosh]

Why steady-state? It had clearly intensified over the last six and twelve hours. From 614z to 1232z, the eye warmed from 9C to 16C, although the cloud tops remained the same -76ishC.

I believe the intensity had leveled off as the core approached the coast. If I remember correctly, it was not intensifying at the time it made landfall, but rather, maintaining-- as per the BoM's wind/pressure estimates. I'll check the records and confirm this later.

[PSUBlizzicane2007]

I believe the intensity had leveled off as the core approached the coast. If I remember correctly, it was not intensifying at the time it made landfall, but rather, maintaining-- as per the BoM's wind/pressure estimates. I'll check the records and confirm this later.

Satellite pictures showed Yasi getting better organized as it approached the coast.

Also, keep in mind that buildings in QLD are built fairly well... generally not like pre-Andrew south Florida.