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Typhoon 23W "Chebi"

Jim Leonard

Over the past 24 hours there has been quite rapid a intensification trend with typhoon Chebi which is about to hit the northern Phillipines. Just yesterday the system was only a 45 mph tropical storm, as of this morning it was brought up to a 145 mph almost supertyphoon. The typhoon is about to strike the same general area of Luzon where the last supertyphoon hit about two weeks ago.
I have been tracking this system for more than ten days when it was out near the International Dateline. The system remained a weak disorganized disturbance until about 48 hours ago when it began to organize and develop.
The Phillipnes can't seem to get a break. I think this is the third major typhoon to hit Luzon this year. It was amazing to see how organized Cimaron was when it hit there a couple of weeks ago.
The Philippines really are getting hit often this year. I've been watching all these latest strong storms as well and what impressed me the most was exactly this RAPID intensification from a small tropical storm into strong typhoon or almost super typhoons like Jim said.
Anyone did any researches around strong CAT4/5 typhoons with El Nino years? I assume this could have some effect there which leads into those rapid intensifications.

The super typhoon Cimaron was a class by itself, unbelivable what an intensification was that!
The cloud structure of typhoon Chebi is quite similar to hurricane Charley at the time of landfall on the SW coast of Florida in 2004. An extremely small storm with very tight inner core. Storms like this dissipate quickly when they move over mountianous terrain such as Luzon's 15k mountains.
The northern Philipines appear to be getting wacked more than usual this year. This is not that unusual as the westpacific averages 30 tropical storms each year and an average of 5 to 8 cross the Phillipines each season. Recent years there have been less than usual unlike Japan who had 10 hits in 2004 which is more than double they're average.
I stayed up a little too late last night watching the intensification, which you don't get to see too often. The timing was such that the NRL web site still had the typhoon satellite imagery labeled at 55 kt, when it was clearly over 100 kt (it was daylight there, and from the vis sat imagery you could see details of the eyewall and the CDO, and it was clearly a mature storm...when I get home tonight I'll update this post with a couple of images and go into a little more detail on that). When they did update it, they went from 55 kt to 115 kt. Ostensibly the pressure drop was something like 40 to 60 mbar in a couple hours. But I want to go back and take another look, because there was, if not an eye, an eye-like feature evident very early on in development, as well as a well-defined ring of convection. I'm wondering if it intensified at a slower rate at first, but didn't appear to be as far along as it actually was. Or if it did intensify just within that short timeframe, but serendipitously had the advantage of an unusually mature structure and organization to build on. And on this one the CIMMS objective ADT was lower than the JTWC and AWFA (usually the AODT runs higher). I need to learn more about Dvorak intensity estimates.
I've been reading about typhoons on wikipedia and found some informations about Chebi where it says the pressure drop this morning was 40hPa in three hours which is totally insane. As Jeff Masters said in his blog another shocking thing is that last three typhoons which hit Luzon had explosive intensification done practically at the same place. There has to be one good spot in the sea.
Hi All ! Long time no write.

Here in south China I closely monitored Xangsane, Cimaron and Chebi hoping that one of them would come close, but nothing.

All three storms shows a very strong tendency of exploding nearby Philippines, with Cimaron being the strongest among the three storms. Chebi, the latest one, after smashing Luzon it managed to stay quite well alive (because of the high speed of movement) and then slowly weaken in the South China Sea for high shear and dry air entrainment (in November China is full of dry air, no cyclone could ever make it to the coast alive...).

Overall, it has been a quiet season for Pacific, normally what happened across October/November should happen in September, with a tendency to affect southern China in at least one case.

Anyway, we got Prapiroon in August, which caused quite a mess around here: winds very strong well inland (I am located 100 km from the coast, exactly north of Macau) and a confirmed F3 tornado 3 km from my home the morning next to landfall, which caused more than 20 deaths..............

Bye to all,
As per the intensification rate of Chebi, here is Dvorak analysis of those moments, is something I have never seen before, worth to be saved and kept !

TPPN10 PGTW 100628
B. 10/0530Z
C. 16.1N/8
D. 125.5E/3
F. T6.0/6.0/D4.0/24HRS STT: D2.5/06HRS (10/0530Z)





Main reason for this intensification seemed to be the linkage of the poleward outflow with a divergent 150 knots jet streak exiting east China, which is not uncommon for the season.

;) Simone
Yes, that was very interesting! Moreso because it was one of those serendipitous things that I happened to catch when I wasn’t really looking for it (like staying up and so seeing the recon report from the flight that went into Wilma at 850 mbar, to find a pressure of, I think it was, 902 mbar, in October 2005). I had checked Chebi earlier in the evening, then looked later on and was surprised to see that it appeared to be organizing rapidly.

What I didn't (still don't) understand is why they didn't go with the data T-number (6.5). AFWA did. And why winds were not as advertised in landfall at Luzon, but weaker. I've been puzzling over it, but haven't had any time recently to go back and look at the satellite imagery.

Either it did intensify that much, and weakened before landfall, or the satellite signature didn't really match the actual windspeeds. Why that would be, I don't know, but it seems like a possibility. Perhaps there was a steady intensification up until landfall, rather than the quick intensification followed by weakening, as far as windspeeds: the apparent rapid pressure drop, as a small well-formed eyewall quickly developed, was followed by a decrease in organization prior to landfall, as the eye clouded over and the convection became less symmetrical. Maybe windspeeds didn’t have time to catch up to the pressure drop before the downturn in organization that appeared on the satellite images, but were only able to increase somewhat, and then continued increasing at a slower rate prior to landfall, still catching up to the pressure.

On the other hand my initial impression had been that there was some weakening before landfall, looking at the outflow (if you try to find other things to go by besides the eye and convective structure). It's harder for me to look at the convection in the West Pacific and get a feel for it, since cloud tops run colder there.

The drop in pressure that was associated with the satellite intensity estimates was, I think, 57 mbar over the six hour period. I'd initially seen a post by a met on storm2k that was titled "40 mbar drop in two hours," (they kept updating the title of the thread, so I think it now reads dissipating in the South China Sea or something like that), but since then, looking back, I don't think it could have been that dramatic.

I also don't know if there were any reliable wind measurements close to the center at landfall, or if windspeeds could be estimated from damage. The lack of damage from Chebi could be in part due to the previous two cyclones already taking down all the trees and buildings that would have come down in a significant storm. Also it appeared the core of stongest winds was very small, and may not have been observed at landfall (like Monica earlier this year).
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Hi Margie, unfortunately there was no reliable wind measurement near the center at landfall, stations in Philippines are sparse and not so reliable, except for a few.

The storm did weaken a little and did loose some of the incredible outflow before landfall. I remember that not only it was linked with the strong jet streak, but also provided a tropical "point of source" in that region (I'm not so technical, but in down-to-earth-words "point of source" means literally the place where the jet streak start from, in this case, a subtropical jet).

Altough would be always difficult to give a real estimate of pressure drop from DVORAK analysis, past recon flights in the Pacific has shown that the strongest deepening rates happens in west Pacific typhoons.

I live in China and as far as I know, I won't be surprised if one day China start, with asian countries, to set up a recon-flights system for west Pacific.

Bye !