ATL: KARL - Post-Tropical - Discussion

[cycloneye]

Extracts from 11 AM discussion:

recent water vapor
imagery suggest that the strong southwesterly shear that has been
plaguing the cyclone for the past few days is beginning to relax.


Although Karl's convective pattern is currently somewhat disheveled
due to the hostile shear and dry mid-level conditions that the
cyclone has been encountering the past several days, the surface
wind field has remained remarkably robust, including a tight
inner-core.

[Kazmit]

Karl is still a TS according to the NHC. They mention it having a tight inner core, so an open wave is not the case here. Might as well keep it as a TS too, for the sake of Bermuda needing to track it.

Although Karl's convective pattern is currently somewhat disheveled
due to the hostile shear and dry mid-level conditions that the
cyclone has been encountering the past several days, the surface
wind field has remained remarkably robust, including a tight
inner-core. The GFS and ECMWF models are forecasting the vertical
wind shear to decrease to less than 5 kt from 24-120 hours, which
favors a strengthening trend, especially since Karl will be moving
29-30C SSTs during that time. However, only a marginally moist
mid-level environment is expected, a condition that could slow down
the intensification process. The official intensity forecast
follows the trend of the previous advisory, showing gradual
strengthening throughout the forecast period, and remains on the
conservative side close to the intensity consensus model IVCN.

[JaxGator]

A ship skirting the east side reported winds of 32 knots.

[Kazmit]

Bermuda almost in the cone.

[Alyono]

Karl is still a TS according to the NHC. They mention it having a tight inner core, so an open wave is not the case here. Might as well keep it as a TS too, for the sake of Bermuda needing to track it.

Although Karl's convective pattern is currently somewhat disheveled
due to the hostile shear and dry mid-level conditions that the
cyclone has been encountering the past several days, the surface
wind field has remained remarkably robust, including a tight
inner-core. The GFS and ECMWF models are forecasting the vertical
wind shear to decrease to less than 5 kt from 24-120 hours, which
favors a strengthening trend, especially since Karl will be moving
29-30C SSTs during that time. However, only a marginally moist
mid-level environment is expected, a condition that could slow down
the intensification process. The official intensity forecast
follows the trend of the previous advisory, showing gradual
strengthening throughout the forecast period, and remains on the
conservative side close to the intensity consensus model IVCN.

Nhc is "wrong" in this case. The ascat is conclusive that this is a wave. I suspect advisories are continuing because there is a very high chance of regeneration. That is why wrong is in quotes. Sceintifically inaccurate but best from a public warning vantage point

[TheAustinMan]

12z ASCAT from the METOP-B satellite.

[floridasun78]

i looking new run from cmc and gfs and other their showing more west track even one got bit north of leedward so calling Bermuda getting hit too early to call

[TropicalAnalystwx13]

12z ASCAT from the METOP-B satellite.

http://i.imgur.com/109gNOa.png

Looks like a tropical cyclone--not a wave--to me.

[cycloneye]

12z GFS after moving far west it recurves and at the same time it goes boom just south of Bermuda.

[Alyono]

Circulation has reformed

[CrazyC83]

I don't think the NHC puts short-lived dissipations in the best track typically, although a case could be made it was a wave/disturbance (albeit TS strength) at 0000Z and 0600Z.

[AutoPenalti]

Looks like circulation reformed to the north?

[cycloneye]

Yes,position of SSD dvorak confirms the relocation.And it went up from 1.0.

18/1745 UTC 18.3N 44.1W T1.5/1.5 KARL -- Atlantic

[Kazmit]

CMC a bit more north, making what looks like landfall on Bermuda as a 64kt hurricane



GFS stronger as an 87kt Category 2, but more south. Giving Bermuda TS force winds.

[wxman57]

Still no tropical storm-force winds, though. Just a depression.

[cycloneye]

12z GFDL.



12z HWRF.

[Kazmit]

One thing to note is the time Karl will take to reach Bermuda. Some models take it to the island by Sunday, while others like the GFS don't let Karl approach Bermuda until Wednesday (but this is probably because it goes on a more westerly track before recurving).

[stormreader]

Storms firing right now at site of "relocated" center near 18.3N.
http://www.ssd.noaa.gov/PS/TROP/floater ... imated.gif

[Kazmit]

A burst of convection on that last frame there.

[cycloneye]

TROPICAL STORM KARL DISCUSSION NUMBER 18
NWS NATIONAL HURRICANE CENTER MIAMI FL AL122016
500 PM AST SUN SEP 18 2016

Deep convection has gradually been increasing and becoming a little
better organized since the previous advisory now that light
upper-level southeasterly flow has replaced the previous hostile
vertical wind shear conditions. Visible satellite imagery and ASCAT
surface wind data from 1200Z-1300Z indicate that Karl's circulation
remains well-defined, especially the inner-core wind field. The
ASCAT data also revealed a large patch of 35-kt winds 60-100 nmi
north and northeast of the center, and that is the intensity used
for this advisory. The ASCAT data supports trimming back the 34-kt
wind radius in the northeastern quadrant.

Karl continues to move westward or 275/13 kt. Karl is expected to
move westward along the southern periphery of the Bermuda-Azores
ridge for the next couple of days, followed by a west-northwestward
motion on days 3-5 as the cyclone approaches a weakness in the ridge
located between Bermuda and the Bahamas. The global and regional
models are in general agreement on this track scenario through 72
hours, After that time, the models diverge significantly with the
GFS, Navy COAMPS, and GFDL models taking Karl farther west as a
weaker and more shallow cyclone, whereas the ECMWF, UKMET, and HWRF
models move Karl more northwestward as a stronger and deeper system.
For now, the official forecast track remains a compromise between
these extremes, close to the consensus model solutions, due to the
lack of a stable, consistent run-to-run forecast by the models.

The GFS and ECMWF models continue to forecast the vertical wind
shear to decrease to less than 10 kt from now through the end of the
forecast period, with near-zero shear values occuring at times
between 72-120 hours. Such low shear values continue to favor a
strengthening trend, especially since Karl will be moving over 30C
SSTs by days 4 and 5. However, a somewhat dry mid-level environment
is expected to temper the intensification process a little due to
occasional intrusions of dry air into the inner-core region of
Karl's circulation. Once the cyclone develops an eye feature, then
strengthening will become more robust due to the low wind shear
conditions and high sea-surface temperatures. Since these
parameters can not be forecast very far in advance, the official
intensity forecast continues to show slow strengthening throughout
the period and remains close to the intensity consensus model IVCN.

FORECAST POSITIONS AND MAX WINDS

INIT 18/2100Z 18.3N 45.0W 35 KT 40 MPH
12H 19/0600Z 18.5N 47.0W 40 KT 45 MPH
24H 19/1800Z 19.0N 49.7W 40 KT 45 MPH
36H 20/0600Z 19.7N 52.2W 45 KT 50 MPH
48H 20/1800Z 20.5N 54.7W 50 KT 60 MPH
72H 21/1800Z 22.9N 59.7W 60 KT 70 MPH
96H 22/1800Z 25.4N 64.2W 70 KT 80 MPH
120H 23/1800Z 28.0N 67.0W 80 KT 90 MPH

$$
Forecaster Stewart