Cyclone Yasi

[k***]

Slowly strengthening? C'mon. It may not have been in RI mode, but it was definitely deepening at a rate that was above climatology, or any other suitable midpoint on the strengthening continuum.

I went to bed and it looked like an upper 3, maybe fake 4. I woke up and was convinced that we were talking cat 5.

[HurricaneJosh]

It wasn't steady state. Adam has already weighed in twice.

And as I have said twice already, there isn't a big difference between slow strengthening and steady-state when we're talking about augmentation of surface winds.

Plus, there is no standard w/p relationship, so I am not sure why you keep bringing it up as if it's ironclad fact.

Yes, there are standards-- standard guidelines that everyone uses. Unlike old P/W assumptions, the newer guidelines from Brown take into account a cyclone's latitude (since of course higher latitude systems have lower winds), and the Knaff-Zehr guidelines also take into account size, environmental pressure, and translational speed. And then from those guidelines, you make adjustments based on a variety of factors, like size and translational speed (if you're using Brown), intensity trend, etc.

The entire NATL reanalysis project uses these standards as a stepping-off point for estimating max winds.

You can disagree all you want with my desire to use some objective P/W standards here, but I will continue to use them. You can say there are no P/W standards-- but, in that case, why do you even care what the central pressure is? You act as if it has no relevance. The reality is that when you factor in central pressure, wind radii, latitude, and intensity trend, you can usually get a pretty decent wind estimate-- not all of the time, but most of the time.

As for the 3 hours part, look at the microwaves you yourself posted--they are classic and really can't be improved upon. Same with the water vapor.

Post which one you mean. The ones prior to landfall didn't look so hot. The ones with the eye on the coast looked good but were so low-res I felt I couldn't draw a decent conclusion from them.

Is it normal for place on the coast "exactly at the landfall point" to have higher pressures than those further away and inland?

You can't seriously be suggesting that Tully's pressure was lower than Clump Point's in a statistically significant way. That is silly. The point is that they were two locations, within a few miles of each other, in the exact path of the center of the eye, with essentially the same pressure-- thus nicely corroborating each other.

Central pressure is not like wind-- where the difference between the immediate coast and a few miles inland is large. A cyclone's pressure rises much more gradually than the winds decrease, so it's reasonable that a station just a few miles inland would have a pressure that's essentially the same as the landfall value.

Not the North Atlantic. Why do you feel generous using it? Your conversions here are really just your own subjective massaging.

I feel generous using it because it yields higher wind readings than one would expect from this basin.

Please go through the BoM's records (like I have) and look at the pressures and max winds of their landfalling cyclones. You'll see their pressures are usually much lower than ours for the same wind speeds.

At the end of the day we are arguing over maybe 5 knots. I think I feel safer being uncertain about where this sits than declaring based upon other basins WP relationships and a few photos that this was definitely not a 5. I think it very well could have been. Do I have evidence? Only speculative...I'll admit that. But based upon how little of an area really experiences max winds in any landfalling system, it's like finding a needle in a haystack. There could be a strip of jungle south of mission beach that caught the absolute max and we'd have missed it since that's not the type of stuff that makes news accounts.

I am not saying it's definitely anything. We can't ever know. What I said is that I strongly doubt, based on my figuring, that this was a USA Cat 5.

[am19psu]

Re: P-W relationships, I'd wager something that there are probably two different ones for this basin. One for when the monsoon trough is present (more like the WPAC) and one for when it isn't (like the ATL/EPAC).

[HurricaneJosh]

Re: P-W relationships, I'd wager something that there are probably two different ones for this basin. One for when the monsoon trough is present (more like the WPAC) and one for when it isn't (like the ATL/EPAC).

Yeah, totally makes sense. So for Yasi, the NATL one would apply better probably-- right?

[am19psu]

Yeah, totally makes sense. So for Yasi, the NATL one would apply better probably-- right?

Yep. I don't know the equations off the top of my head, but I'm sure ambient pressure is somewhere in the new P-W relations.

[HurricaneJosh]

Yep. I don't know the equations off the top of my head, but I'm sure ambient pressure is somewhere in the new P-W relations.

The Knaff-Zehr version takes ambient pressure (and size) into account-- the Brown version does not. I think of Brown more as a stepping-off point-- you have to really massage the initial value.

[k***]

And as I have said twice already, there isn't a big difference between slow strengthening and steady-state when we're talking about augmentation of surface winds.

What about steady state versus a clearly moderate rate of strengthening...a sudden jump of 7C in the eye isn't slow strengthening. Another thing that I haven't mentioned because I just thought about it and it's fairly anecdotal, but it seems strengthening storms tend to hold their eye better for a couple hours as they plow onshore--alex, richard etc. This one did that.

Yes, there are standards-- standard guidelines that everyone uses. (Unlike old P/W assumptions, the newer guidelines from Brown and Knaff-Zehr take into account a cyclone's latitude, since of course higher latitude systems have lower winds.) And then from those guidelines, you make adjustments based on a variety of factors, like size, intensity trend, etc.

Another thing that hasn't been discussed is forward motion--this one was booking and that is another adjustment that needs to be made when we are playing with these relationships. Funny that you ignore that.

The entire NATL reanalysis project uses these standards as a stepping-off point for estimating max winds.

And the North Atlantic relationship is different. In fact, Austrialia uses three different WP relationships in their offices, and Brisbane's has been found to be fairly inaccurate

http://journals.ametsoc.org/doi/full/10.1175/WAF965.1

You can disagree all you want with my desire to use some objective P/W standards here, but I will continue to use them. You can say there are no P/W standards-- but, in that case, why do you even care what the central pressure is? You act as if it has no relevance. The reality is that when you factor in central pressure, wind radii, latitude, and intensity trend, you can usually get a pretty decent wind estimate-- not all of the time, but most of the time.

The whole point is that scientists haven't worked out a consensus on the appropriate relationship, and even then they are just general guidelines that are subject to serious error bars. To continually take other basins relationships and then extrapolate them may be better than just guessing, but not much better. And certainly not conclusive.

Post which one you mean. The ones prior to landfall didn't look so hot. The ones with the eye on the coast looked good but were so low-res I felt I couldn't draw a decent conclusion from them.

You posted them. 671 I think. If you don't think those microwaves could support a 5 you are CRAZY. You posted a high rez and a low rez---the high rez was nice and the low rez was sweet too. I don't know why you can't use them to paint a picture, even if not conclusive.

You can't seriously be suggesting that Tully's pressure was lower than Clump Point's in a statistically significant way. That is silly. The point is that they were two locations, within a few miles of each other, in the exact path of the center of the eye, with essentially the same pressure-- thus nicely corroborating each other.

Tully and Mission Beach are 11 miles apart and semi-parallel to the track of the storm. Cardwell caught Eyewall and is 20 miles from there. Somewhere inbetween could have been the true area of lowest pressure.

Central pressure is not like wind-- where the difference between the immediate coast and a few miles inland is large. A cyclone's pressure rises much more gradually than the winds decrease, so it's reasonable that a station just a few miles inland would have a pressure that's essentially the same as the landfall value.

That's fair.

I feel generous using it because it yields higher wind readings than one would expect from this basin.

Please go through the BoM's records (like I have) and look at the pressures and max winds of their landfalling cyclones. You'll see their pressures are usually much lower than ours for the same wind speeds.

It's just not appropriate--they are different basins. As for BOM records, they are imperfect at best. They have never had recon, have sparse data collection, and have some seriously egregious errors in their database (monica 916?).

I am not saying it's definitely anything. We can't ever know. What I said is that I strongly doubt, based on my figuring, that this was a USA Cat 5.

I've been arguing with you mostly because I find your attitude to be pretty smug. Maybe that's just online miscommunication, but your ongoing attempts to downplay the strengthening trend are the lolz.

[k***]

Five different WPRs have been used at the operational TC centers throughout the world. They are the following:

Atkinson and Holliday (1977, 1975), used at the Regional Specialized Meteorological Center (RSMC) on La Reunion island, RSMC Fiji, the Perth tropical cyclone center, and at the Joint Typhoon Warning Center;

Koba et al. (1990) used at the RSMC Tokyo;

Love and Murphy (1985) used in the Australian Northern Territory tropical cyclone warning center in Darwin;

a method attributed to Crane used at the Brisbane tropical cyclone warning center (Harper 2002); and

Dvorak (1975) (i.e., the Atlantic part of the table column in Fig. 5) is used for the Atlantic and east Pacific at the National Hurricane Center/Tropical Prediction Center (NHC/TPC) and for the central Pacific at the Central Pacific Hurricane Center.

[HurricaneJosh]

kush, those are all ancient guidelines. The new versions are Brown (2006) and Knaff-Zehr (2007). That's what's being used now, and even the BoM referenced Knaff-Zehr in their reanalysis work on Tracy.

[k***]

Can I get a link to this knaff-zehr article?

nvm...that was the article i posted! I thought I had clicked on the brown article.

[am19psu]

Can I get a link to this knaff-zehr article?

http://journals.ametsoc.org/doi/pdf/10.1175/WAF965.1

[aslkahuna]

Re: P-W relationships, I'd wager something that there are probably two different ones for this basin. One for when the monsoon trough is present (more like the WPAC) and one for when it isn't (like the ATL/EPAC).

That was the point brought out with the JTWC analysis of the passage of STY Paka over Guam. The in-situ wind reports and damage surveys clearly supported a 130 kt STY as it passed Guam but the pressure reported at Andersen AB on the north end of the island did not and could not be made to conform with the W/P value of 910 mb for such as storm but a higher one. Paka was a December storm and by then the monsoon trough is usually not a factor in WPAC-certainly not at the latitude of Guam. This lead the JTWC forecasters to conclude that for off season storms like Paka a higher pressure for a given intensity was likely since ambient pressures are then higher. In their report they suggested that the NATL W/P relationship seemed to have worked well with Paka.

Steve

[HurricaneJosh]

What about steady state versus a clearly moderate rate of strengthening...a sudden jump of 7C in the eye isn't slow strengthening. Another thing that I haven't mentioned because I just thought about it and it's fairly anecdotal, but it seems strengthening storms tend to hold their eye better for a couple hours as they plow onshore--alex, richard etc. This one did that.

Another thing that hasn't been discussed is forward motion--this one was booking and that is another adjustment that needs to be made when we are playing with these relationships. Funny that you ignore that.

And the North Atlantic relationship is different. In fact, Austrialia uses three different WP relationships in their offices, and Brisbane's has been found to be fairly inaccurate

http://journals.ametsoc.org/doi/full/10.1175/WAF965.1

The whole point is that scientists haven't worked out a consensus on the appropriate relationship, and even then they are just general guidelines that are subject to serious error bars. To continually take other basins relationships and then extrapolate them may be better than just guessing, but not much better. And certainly not conclusive.

You posted them. 671 I think. If you don't think those microwaves could support a 5 you are CRAZY. You posted a high rez and a low rez---the high rez was nice and the low rez was sweet too. I don't know why you can't use them to paint a picture, even if not conclusive.

Tully and Mission Beach are 11 miles apart and semi-parallel to the track of the storm. Cardwell caught Eyewall and is 20 miles from there. Somewhere inbetween could have been the true area of lowest pressure.

That's fair.

It's just not appropriate--they are different basins. As for BOM records, they are imperfect at best. They have never had recon, have sparse data collection, and have some seriously egregious errors in their database (monica 916?).

I've been arguing with you mostly because I find your attitude to be pretty smug. Maybe that's just online miscommunication, but your ongoing attempts to downplay the strengthening trend are the lolz.

• If the BoM can reference NATL W/P work when analyzing their systems, I feel OK doing it, too-- just to get a starting number.
  
• You're right-- Tully and Mission Beach are a little farther apart than I remembered-- but not far enough to change my feeling that their readings corroborate each other, especially given that they're along the basic path that the center took. I plotted the BoM's coordinates, and both Mission Beach and Tully were in the eye and are within a few mi of the exact track of the eye's center. Given that the eye was pretty large and the system as a whole was very large, I believe they probably got close to the lowest pressures. (In a microcane, the few miles could make more of a difference, I'd think.)
  
• Again-- I have to keep saying it-- if anything, the NATL P/W relationship is generous for this region, meaning it would yield values closer to what you think it should be-- so I don't know why you're complaining about it. Again, please go through the BoM's records and look at the pressures and winds for landfalling Aussie cyclones. (I don't think it's reasonable to be so dismissive of them.) You will see that they generally have much lower winds for the same pressures, compared to what we're accustomed to. Please look-- because having that perspective will help you understand why I'm not all "Omg it was a Cat 5!!11!1"
  
• How is it smug for me to agree with the BoM, who did not show strengthening leading up to landfall? I apologize for deferring to the official agency that was in charge of monitoring the cyclone.
  

[k***]

Be back later...my interwebs are intolerably messed up now and I keep losing chunks of posts.

[HurricaneJosh]

P.S. I was thinking the cyclone's forward motion would really augment winds left of the center, but it slowed a bit before landfall and was moving at a more normal rate when it crossed the coast-- thus I'm not giving any "bonus knots" for that.

[am19psu]

P.S. I was thinking the cyclone's forward motion would really augment winds left of the center, but it slowed a bit before landfall and was moving at a more normal rate when it crossed the coast-- thus I'm not giving any "bonus knots" for that.

Actually, it sped back up right at landfall. It was moving SW at 19kts, did a trochoidal wobble which slowed it down, then accelerated again right at landfall.

[HurricaneJosh]

Actually, it sped back up right at landfall. It was moving SW at 19kts, did a trochoidal wobble which slowed it down, then accelerated again right at landfall.

Did it? The advices had it slowing down-- from 30 km/hr for most of the day before to 25 km/hr as it neared the coast-- but I don't remember exactly what they said right at landfall. I'll check over the advices later.

[Scott747]

Video of Dunk Island with some aerial footage. Video link is on the right of the article.

http://www.theaustralian.com.au/in-depth/cyclone-yasi/new-storm-surge-threatens-cairns-and-townsville-as-cyclone-yasi-weakens-heads-inland/story-fn7rj0ye-1225999868555

[Ed Lizard]

<LI>How is it smug for me to agree with the BoM, who did not show strengthening leading up to landfall? I apologize for deferring to the official agency that was in charge of monitoring the cyclone.

Nitpicking, but the UN WMO RSMC is Fiji, not the BoM.

http://www.metoffice.gov.uk/weather/tropicalcyclone/warnings.html

The BOM is listed as "other", like the Canadian Hurricane Centre...

Anyway, continue on about the 5 or 10 knot difference of opinion.

I had never heard of Knaff before.

[HurricaneJosh]

By the way-- and I'm going to get so flamed for saying this-- but if I wanted to followed my normal MO with these wind estimates, I would harshly penalize Yasi for its large size and estimate something closer to 120 kt. The fact that Townsville-- almost 120 mi S of the track!!-- practically had hurricane winds (when converted from 10-min to 1-min) is ridiculous and suggests a very broad circulation. But I think that would cause several of you to attack me, and I don't feel like dealing with that, so I'll bow to peer pressure and just say 130 kt.

In all seriousness... I'm cool with at least 130 kt because, despite the very large size. The discussion here has had a slight impact on my thinking. Slight.

1. It was certainly in a healthy state when it crossed the coast, and comments by am19psu and kush make me feel perhaps it was strengthening a tad (although not bombing out).

2. As per am19psu's comment, it actually did cross the coast at a brisk speed (~19 kt), so that motion probably augmented the winds in the S eyewall a bit.

3. The MW image of the eye on the coast does show some really good structure. I was slightly hesitant to really factor it in because it's so low-res, but you can see that red ring is fully closed around the center.

4. The trees on Dunk Island got pretty stripped.

[HurricaneJosh]

Nitpicking, but the UN WMO RSMC is Fiji, not the BoM.

I'm not understanding. The cyclone originated in Fiji turf, but once it crossed 160E, it was in BoM turf. BoM's region starts W of 160E-- it's not Fiji's region.

[Ed Lizard]

I'm not understanding. The cyclone originated in Fiji turf, but once it crossed 160E, it was in BoM turf. BoM's region starts W of 160E-- it's not Fiji's region.

The same way a typhoon approaching the Philippines will have warnings issued by Pagasa, but the official United Nations World Meteorological Organization Regional Specialty Meteorology Center is the JMA.

Would I trust Fiji over Australia? Probably not. But it is the UN.

[HurricaneJosh]

The same way a typhoon approaching the Philippines will have warnings issued by Pagasa, but the official United Nations World Meteorological Organization Regional Specialty Meteorology Center is the JMA.

Would I trust Fiji over Australia? Probably not. But it is the UN.

Read it again. After Fiji, it says: "(South Pacific Ocean east of 160° E and north of 25° S)". They have no jurisdiction over the waters around Australia.

Look here: http://www.nhc.noaa.gov/gifs/wmo-tcp2.jpg

[Ed Lizard]

Checking Wiki, Australia has 3 TCWCs, but the RMSC is Fiji.

Well, checking Wiki, a TCWC is official per the WMO for naming cyclones and issuing advisories.

[Ed Lizard]

Read it again. After Fiji, it says: "(South Pacific Ocean east of 160° E and north of 25° S)". They have no jurisdiction over the waters around Australia.

Look here: http://www.nhc.noaa....fs/wmo-tcp2.jpg

Ah, I stand corrected.

[k***]

By the way-- and I'm going to get so flamed for saying this-- but if I wanted to followed my normal MO with these wind estimates, I would harshly penalize Yasi for its large size and estimate something closer to 120 kt. The fact that Townsville-- almost 120 mi S of the track!!-- practically had hurricane winds (when converted from 10-min to 1-min) is ridiculous and suggests a very broad circulation. But I think that would cause several of you to attack me, and I don't feel like dealing with that, so I'll bow to peer pressure and just say 130 kt.

In all seriousness... I'm cool with at least 130 kt because, despite the very large size. The discussion here has had a slight impact on my thinking. Slight.

1. It was certainly in a healthy state when it crossed the coast, and comments by am19psu and kush make me feel perhaps it was strengthening a tad (although not bombing out).

2. As per am19psu's comment, it actually did cross the coast at a brisk speed (~19 kt), so that motion probably augmented the winds in the S eyewall a bit.

3. The MW image of the eye on the coast does show some really good structure. I was slightly hesitant to really factor it in because it's so low-res, but you can see that red ring is fully closed around the center.

4. The trees on Dunk Island got pretty stripped.

You'd look like such a tool if you estimated 120kts out of that. You'd definitely get attacked.

I'm fine with agreeing to disagree over the fine details--regardless, this was definitely one of the most impressive landfalls of the decade, irrespective of whether it was a high 4 or low 5.

[k***]

Another thing I thought of while out grocery shopping was: Why can't an Atlantic analog for this be the 1928 San Felipe? ~930, large, cat 5 hit on PR.

[HurricaneJosh]

You'd look like such a tool if you estimated 120kts out of that. You'd definitely get attacked.

I'm fine with agreeing to disagree over the fine details--regardless, this was definitely one of the most impressive landfalls of the decade, irrespective of whether it was a high 4 or low 5.

No argument there. It definitely was.

In the end, our disagreement is over 5 kt and whether it was possibly a USA Cat 5-- you think it was quite possible, I think it was unlikely. Relatively small differences in the end.

You are still my friend, ya little b*tch!!1!

[HurricaneJosh]

Another thing I thought of while out grocery shopping was: Why can't an Atlantic analog for this be the 1928 San Felipe? ~930, large, cat 5 hit on PR.

I'm not aware of the dimensions of that one offhand. It was recently reanalyzed, so I'll do some reading about it tonight.

[am19psu]

Not to mention that 5 kts is well within the error bars of any satellite based intensity estimation or P-W estimation...