Typhoon Chanchu

[Josh Morgerman]

Thanks, Scott, for that info. Interesting that the Hong Kong Observatory (HKO) recurves to the storm to the NE and spares Hong Kong a direct hit. I did some additional research this morning and also checked out the Japan Meteorological Agency (JMA), which I've been told is the "official" source for info Re: systems in this region.

As with tropical cyclones threatening Australia, the different agencies covering the South China Sea give conflicting views.

INTENSITY
As of the time of my writing this, the JTWC estimates 120 kt. The JMA indicates ~104 kt when their 10-min average value of 90 kt is converted to a 1-min value. That's a big difference. Both agencies now anticipate weakening as Chanchu moves N-- so the prognosis does not seem quite as dire as last night. Even so, the JTWC forecast still implies a direct hit on Hong Kong by a 105-kt typhoon (Cat 3 USA).

I notice in the latest satellite imagery (below) that the N portions of the system seem to eroding a bit.

TRACK
Again, opinions significantly diverge. The JTWC keeps Chanchu moving pretty-much due N, to Hong Kong, whereas the JMA (and HKO) indicate significant NE recurvature, sparing Hong Kong a direct hit.

OVERALL
From a standpoint of both intensity and track, the JTWC prediction is the most threatening to Hong Kong. I would be curious to know what causes the rather large differences between the JTWC's and JMA's opinions on this situation.

Please note: This image will update dynamically and the commentary above will no longer apply as time passes.

 

[mark humpage]

I am reliably informed that the forecasters at the JTWC only have a couple of years tropical forecasting experience.

I'd go with JMA on the intensity.

Mark

 

[Mark Farnik]

All of a sudden the JTWC is calling for signifcant weakening as Chanchu approaches land, having it as a 85 knot storm hitting HK around 12Z on the 17th. Any explanations for why they are suddenly predicting this weakening trend and adjusting the landfall intensity so far downward? I'm confused, as the SST's and shear seem conducive to Chanchu remaining a Super Typhoon until landfall. Either something has changed drastically in the last 6 hours in regards to favorability for maintaining its present strength or intensifying or they're trying to prevent widespread panic in HK (which, if that is the case, which I hope it is not, is an incredibly bonehead maneuver on the part of the JTWC)
Any explanations on this dramatic change in forecast?

 

[mark humpage]

All of a sudden the JTWC is calling for signifcant weakening as Chanchu approaches land, having it as a 85 knot storm hitting HK around 12Z on the 17th. Any explanations for why they are suddenly predicting this weakening trend and adjusting the landfall intensity so far downward? I'm confused, as the SST's and shear seem conducive to Chanchu remaining a Super Typhoon until landfall. Either something has changed drastically in the last 6 hours in regards to favorability for maintaining its present strength or intensifying or they're trying to prevent widespread panic in HK (which, if that is the case, which I hope it is not, is an incredibly bonehead maneuver on the part of the JTWC)
Any explanations on this dramatic change in forecast?
[/b]

The JTWC is now calling storm intensity in line with JWA. Obviously the JTWC have been overplaying the call, which would explain my last comment with regards their forecasters inexperience. Stick with the JWA, which has been pretty consistent all along to date.
Mark

 

[Josh Morgerman]

Very interesting development. In addition to the significant weakening now indicated (85 kt at landfall), the JTWC track is also curving more to the right-- and coming more in line with the JMA's. This puts Hong Kong on the weaker side of the system.

What a difference a day makes...

 

[mark humpage]

Yes what a 24 hrs :blink: There is also still plenty of moisture between now and landfall for it to change again. We watch with interest.

Mark

 

[mark humpage]

SST's are currently riding 27 deg just off land. Can't find any buoy data further out near present position mind.

Mark

 

[mark humpage]

Found them http://www7320.nrlssc.navy.mil/modas2d/

The typhoon is currently in waters of 30/31 deg (the warmest in the south china sea). Temps are decreasing down to 27 deg nearer land. I would therefore agree with JMA in their assessment of decreasing intensity. Looking like a Cat 2 landfall.

Mark

 

[Josh Morgerman]

The threat to Hong Kong continues to diminish. The latest JTWC forecast is much more aligned with the JMA-- with both now indicating a moderate typhoon making landfall well E of Hong Kong. The JMA suggests ~80 kt around landfall (when their 10-min value of 70 kt is converted to a 1-min value using a standard 1.15 factor) whereas the JTWC-- always more bullish-- suggests 85 kt. Either way, there is consensus that Chanchu will be a borderline Cat 1/Cat 2 USA at landfall in China.

 

[Josh Morgerman]

The JTWC and JMA are in relatively good agreement that Chanchu will come ashore or graze the China coast near the city of Shantou within the next 12 hours or so as an 80-kt (Cat 1 USA) typhoon.

I am certainly happy for Hong Kong. But of course that tiny () side of me that sees hurricanes as a kind of grand natural theatre can only describe this ending as a slight anti-climax.

 

[Josh Morgerman]

The 12Z updates from JTWC and JMA have the center very close the SE China coastline, near Shantou, moving NNE.

The JTWC puts the intensity at a robust 90 kt, whereas the JMA puts it at ~86 kt (when their 10-min value of 75 kt is converted to a 1-min value using a standard factor of 1.15). Given this, both agencies put the intensity near landfall at Cat 2 USA.