ATL: SEBASTIEN - Post-Tropical

[DioBrando]

Sebastien is turning out to be a really interesting storm! It’s also one of the longest lived storms of 2019!

No one:

Dorian, Humberto, Lorenzo: Sebasti-WHO?

[Sciencerocks]

[Sciencerocks]

Tropical Storm Sebastien Discussion Number 18
NWS National Hurricane Center Miami FL AL202019
500 PM AST Sat Nov 23 2019

Sebastien's cloud pattern is beginning to resemble that of an
extratropical cyclone, with a shield of moderately cold cloud tops
extending well to the north of the cyclone's surface center. That
said, Sebastien is still producing enough convection near its center
to be considered a tropical cyclone for now. ASCAT-B data that
arrived shortly after the last advisory was issued had support for
55 kt and that is the basis for the initial intensity. The ASCAT
data also showed that the surface wind circulation of Sebastien is
elongated but still closed.

Sebastien is accelerating northeastward, with an initial motion of
045/26 kt. Most of the 12Z models show a significantly faster
northeastward track for the tropical storm and the official forecast
has been adjusted accordingly. However, the NHC forecast is slower
than the model consensus and additional large changes may be
required in the next advisory. Confidence in the track forecast
remains low due to the continued lack of run-to-run consistency
amongst the models. With regard to intensity, a majority of the
guidance calls for little change in strength since it seems that
baroclinic forcing will at least offset the negative influences of
decreasing SSTs and high shear during the next day or two. The NHC
intensity forecast is very near the consensus. Cyclone phase-space
diagrams derived from the GFS and ECMWF indicate that extratropical
transition could occur by Sunday afternoon, but the NHC forecast is
slightly more conservative. The reality is that Sebastien could
become extratropical or open into a trough at nearly any time
between this evening and early next week.

Sebastien or its remnants are expected to bring gusty winds and
rain to the Azores beginning on Sunday. Please see products issued
by the Portuguese Institute for the Sea and the Atmosphere (IPMA)
for more information.


FORECAST POSITIONS AND MAX WINDS

INIT 23/2100Z 32.4N 45.4W 55 KT 65 MPH
12H 24/0600Z 35.0N 41.5W 55 KT 65 MPH
24H 24/1800Z 37.8N 35.3W 55 KT 65 MPH
36H 25/0600Z 40.9N 27.6W 55 KT 65 MPH...POST-TROP/EXTRATROP
48H 25/1800Z 44.8N 19.3W 50 KT 60 MPH...POST-TROP/EXTRATROP
72H 26/1800Z...DISSIPATED

$$
Forecaster Zelinsky

[Astromanía]

Lol this is still around

[Buck]

Wish I didn't want him to peak at hurricane status so bad, because it doesn't matter and his longevity this time of year was interesting anyway.

[DioBrando]

AHAHHAHA WHAT


...SEBASTIEN REFUSES TO WEAKEN AS IT RACES NORTHEASTWARD...

"Sebastien is quickly moving up on my list of most annoying storms
during the 2019 season, and hopefully this isn't another night of
it making my forecast look silly. I think (hope?) the intensity
outlook is getting easier since the storm will be moving over
sub-20C waters by tomorrow morning. There are no signs of
significant upper-level cooling at that time, so Sebastien will
probably be struggling to produce any organized deep convection.
Since baroclinic forcing also appears to be on the wane, a slow
weakening is anticipated, and a more complete extratropical
transition is forecast by this time tomorrow. This is also
indicated by cyclone phase space diagrams derived from the GFS and
ECMWF models. While I might have a little more confidence in this
prediction than a couple of days ago, I also wouldn't be surprised
if Sebastien had another trick up its sleeve."

LOL WHAT

could he pull a humberto and strengthen using baroclinic forcing while peaking at a high latitude though?

[TallyTracker]

401
WTNT45 KNHC 240255
TCDAT5

Tropical Storm Sebastien Discussion Number 19
NWS National Hurricane Center Miami FL AL202019
1100 PM AST Sat Nov 23 2019

Over the large scale, Sebastien appears to be undergoing
extratropical transition, with a large cirrus shield on the
northern side of the storm and unimpressive convection overall.
Near the center, however, the storm still has a small inner core,
with what appears to be a faint eye feature forming during the past
few hours in conventional satellite imagery. This feature also
shows up in recent microwave data, suggesting that Sebastien still
has more of its tropical character than a cursory look would
indicate. Thus, Sebastien is held as a tropical cyclone and, since
Dvorak and SATCON estimates remain at 55 kt, the initial wind speed
is held at that value. Unfortunately all 3 scatterometer satellites
missed the cyclone this evening.

Sebastien is quickly moving up on my list of most annoying storms
during the 2019 season, and hopefully this isn't another night of
it making my forecast look silly. I think (hope?) the intensity
outlook is getting easier since the storm will be moving over
sub-20C waters by tomorrow morning. There are no signs of
significant upper-level cooling at that time, so Sebastien will
probably be struggling to produce any organized deep convection.
Since baroclinic forcing also appears to be on the wane, a slow
weakening is anticipated, and a more complete extratropical
transition is forecast by this time tomorrow. This is also
indicated by cyclone phase space diagrams derived from the GFS and
ECMWF models. While I might have a little more confidence in this
prediction than a couple of days ago, I also wouldn't be surprised
if Sebastien had another trick up its sleeve.

The storm is accelerating northeastward, now estimated at
045/27 kt. The evening model guidance continues the trend noted
by my predecessor of a faster motion, so the new NHC prediction is
shifted in that direction, and somewhat to the north. Sebastien or
its extratropical remnants are expected to bring gusty winds and
rain to the Azores beginning on Sunday. Please see products issued
by the Portuguese Institute for the Sea and the Atmosphere (IPMA)
for more information.


FORECAST POSITIONS AND MAX WINDS

INIT 24/0300Z 34.4N 43.1W 55 KT 65 MPH
12H 24/1200Z 37.0N 38.7W 55 KT 65 MPH
24H 25/0000Z 40.1N 31.1W 50 KT 60 MPH...POST-TROP/EXTRATROP
36H 25/1200Z 43.9N 22.3W 50 KT 60 MPH...POST-TROP/EXTRATROP
48H 26/0000Z 48.0N 14.5W 45 KT 50 MPH...POST-TROP/EXTRATROP
72H 27/0000Z...DISSIPATED

$$
Forecaster Blake

The forecasters are starting to get really funny with Sebastien! Starting to remind me of Hurricane Epsilon discussions! lol

[DioBrando]

401
WTNT45 KNHC 240255
TCDAT5

Tropical Storm Sebastien Discussion Number 19
NWS National Hurricane Center Miami FL AL202019
1100 PM AST Sat Nov 23 2019

Over the large scale, Sebastien appears to be undergoing
extratropical transition, with a large cirrus shield on the
northern side of the storm and unimpressive convection overall.
Near the center, however, the storm still has a small inner core,
with what appears to be a faint eye feature forming during the past
few hours in conventional satellite imagery. This feature also
shows up in recent microwave data, suggesting that Sebastien still
has more of its tropical character than a cursory look would
indicate. Thus, Sebastien is held as a tropical cyclone and, since
Dvorak and SATCON estimates remain at 55 kt, the initial wind speed
is held at that value. Unfortunately all 3 scatterometer satellites
missed the cyclone this evening.

Sebastien is quickly moving up on my list of most annoying storms
during the 2019 season, and hopefully this isn't another night of
it making my forecast look silly. I think (hope?) the intensity
outlook is getting easier since the storm will be moving over
sub-20C waters by tomorrow morning. There are no signs of
significant upper-level cooling at that time, so Sebastien will
probably be struggling to produce any organized deep convection.
Since baroclinic forcing also appears to be on the wane, a slow
weakening is anticipated, and a more complete extratropical
transition is forecast by this time tomorrow. This is also
indicated by cyclone phase space diagrams derived from the GFS and
ECMWF models. While I might have a little more confidence in this
prediction than a couple of days ago, I also wouldn't be surprised
if Sebastien had another trick up its sleeve.

The storm is accelerating northeastward, now estimated at
045/27 kt. The evening model guidance continues the trend noted
by my predecessor of a faster motion, so the new NHC prediction is
shifted in that direction, and somewhat to the north. Sebastien or
its extratropical remnants are expected to bring gusty winds and
rain to the Azores beginning on Sunday. Please see products issued
by the Portuguese Institute for the Sea and the Atmosphere (IPMA)
for more information.


FORECAST POSITIONS AND MAX WINDS

INIT 24/0300Z 34.4N 43.1W 55 KT 65 MPH
12H 24/1200Z 37.0N 38.7W 55 KT 65 MPH
24H 25/0000Z 40.1N 31.1W 50 KT 60 MPH...POST-TROP/EXTRATROP
36H 25/1200Z 43.9N 22.3W 50 KT 60 MPH...POST-TROP/EXTRATROP
48H 26/0000Z 48.0N 14.5W 45 KT 50 MPH...POST-TROP/EXTRATROP
72H 27/0000Z...DISSIPATED

$$
Forecaster Blake

The forecasters are starting to get really funny with Sebastien! Starting to remind me of Hurricane Epsilon discussions! lol

I've literally just posted that before you lol

anyway, I wonder what the next advisory would be lel

[AnnularCane]

Is it because Sebastien hasn't been absorbed by the front yet? Because I don't know what annoying thing he's doing otherwise.

[galaxy401]

Is it because Sebastien hasn't been absorbed by the front yet? Because I don't know what annoying thing he's doing otherwise.

Hurricane season is nearly over and Thanksgiving is coming soon. The forecasters are just done at this point and don’t want any stubborn systems hanging around.

[Sciencerocks]

[Sciencerocks]

Tropical Storm Sebastien Discussion Number 20
NWS National Hurricane Center Miami FL AL202019
500 AM AST Sun Nov 24 2019

Sebastien is on the slow boat to becoming fully extratropical.
Just within the past few hours, the cyclone has taken on an
appearance more resembling a subtropical cyclone, with all of its
deep convection located in a band to the north of the center and it
being co-located with an upper-level shortwave trough. Based on
Sebastien's evolving structure, TAFB provided a subtropical
classification of ST3.5. Combining this estimate with the most
recent ADT and SATCON estimates, the initial intensity remains 55
kt.

Since Sebastien's extratropical transition has been so drawn out,
it's difficult to pinpoint exactly when the process will be
complete. Phase-space diagrams from the GFS and ECMWF models
indicate that the cyclone will be deep cold core within the next
6-12 hours. However, these models keep the low-level vortex
separate from a second upstream upper-level trough for the next 30
hours, and they also keep deep convection going (in simulated
satellite imagery) near but to the north of the center for that same
amount of time. Because of deep-layer shear around 40 kt and sea
surface temperatures near 20C, the official forecast continues to
show extratropical transition complete by 24 hours, but that
forecast should be considered with a margin of error of plus or
minus 12 hours. Regardless of its status, Sebastien is forecast to
only gradually lose strength over the next 48 hours and is likely to
bring gusty winds and heavy rains to portions of the Azores later
today and tonight. Please see products issued by the Portuguese
Institute for the Sea and the Atmosphere (IPMA) for more
information.

The northeastward acceleration continues, with Sebastian moving
050/29 kt. Additional acceleration is expected during the next 24
hours, with the new NHC track forecast a little faster than the
previous iteration and generally a blend of the TVCN and HCCA
consensus aids. No forecast points are provided starting at 72
hours since by that time Sebastien is expected to have merged with
another weather system southwest of Ireland and the United Kingdom.
This larger complex system could bring gusty winds and heavy rains
to portions of western Europe within the next few days.


FORECAST POSITIONS AND MAX WINDS

INIT 24/0900Z 36.0N 40.0W 55 KT 65 MPH
12H 24/1800Z 38.5N 34.8W 55 KT 65 MPH
24H 25/0600Z 42.1N 26.2W 50 KT 60 MPH...POST-TROP/EXTRATROP
36H 25/1800Z 46.2N 17.5W 45 KT 50 MPH...POST-TROP/EXTRATROP
48H 26/0600Z 50.0N 11.4W 45 KT 50 MPH...POST-TROP/EXTRATROP
72H 27/0600Z...MERGED WITH ANOTHER WEATHER SYSTEM

$$
Forecaster Berg

[supercane4867]

It's rare to see a such long track storm this late in the season.

[Sciencerocks]

[Buck]

It sure has been the year of the Azores!

[cycloneye]

Is over but it made a good run to Hurricane and lasted longer than expected adding a few ACE units to the North Atlantic.

Post-Tropical Cyclone Sebastien Discussion Number 23
NWS National Hurricane Center Miami FL AL202019
1100 PM AST Sun Nov 24 2019

Sebastien has lost its tropical characteristics this evening. The
deep convection has decoupled from the low-level circulation, and
these features are now separated by a distance of 100 n mi and
increasing. Two partial ASCAT passes revealed that the surface low
is becoming stretched out, and there is some evidence of a boundary,
possibly a front, extending northeast from the center. Furthermore,
recent observations from Corbo and Flores islands in the Azores
indicated a slight temperature decrease as the center passed by to
the north of those islands, suggesting that a weak cold front is
associated with the the cyclone. Based on all of these data, there
is high confidence that Sebastien has transitioned to an
extratropical cyclone. The initial advisory intensity is 50 kt which
is based on 47 kt winds sampled by the scatterometer and a
subjective intensity estimate from TAFB.

Post-tropical cyclone Sebastien is moving northeastward at 35 kt,
embedded in the strong flow to the southeast of a mid- to upper-
level trough. This motion, and the cyclone's current intensity, is
expected to persist for the next day or so, before the cyclone
merges with a higher-latitude low.

The cyclone will likely bring gusty winds and heavy rains to
portions of the Azores through Monday morning. Please see products
issued by the Portuguese Institute for the Sea and the Atmosphere
(IPMA) for more details.

Additional information on this system can be found in:

High Seas Forecasts issued by Meteo France under WMO header FQNT50
LFPW and on the web at
http://www.meteofrance.com/previsions-m ... randlarge/
metarea2.

FORECAST POSITIONS AND MAX WINDS

INIT 25/0300Z 41.0N 28.9W 50 KT 60 MPH...POST-TROP/EXTRATROP
12H 25/1200Z 43.6N 22.7W 50 KT 60 MPH...POST-TROP/EXTRATROP
24H 26/0000Z 48.1N 14.2W 50 KT 60 MPH...POST-TROP/EXTRATROP
36H 26/1200Z...MERGED WITH ANOTHER LOW

$$
Forecaster Latto

[Sciencerocks]