ATL: SEBASTIEN - Post-Tropical

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Re: ATL: SEBASTIEN - Tropical Storm

#81 Postby Sciencerocks » Thu Nov 21, 2019 10:32 pm

Tropical Storm Sebastien Discussion Number 11
NWS National Hurricane Center Miami FL AL202019
1100 PM AST Thu Nov 21 2019

Sebastien continues to produce a central dense overcast and a large
band on the southeastern side of the circulation. Recent
scatterometer data indicate that the maximum winds are at least 45
kt and, since there has been little overall change in the satellite
presentation within the past several hours, the initial wind speed
will stay 50 kt.

Two notable changes have been made on this forecast. As
foreshadowed in the previous forecast, the models are no longer
rapidly accelerating the storm to the northeast ahead of a
mid-latitude trough. Instead, there is better agreement tonight on a
steadier motion to the northeast due to the trough in the short
term. Sebastien will then continue moving northeastward embedded in
the mid-latitude southwesterly flow over the weekend. The new
forecast is substantially slower than the last one, but is still on
the faster side of the guidance due to continuity concerns.

The second significant change is that Sebastien is no longer
expected to become a hurricane. The cyclone will soon be moving
over sub-26C waters with strong shear, and it seems unlikely to
intensify much in these conditions. Model intensity guidance
continues to decrease, and the NHC forecast follows that trend.
Weakening should start by the weekend over even cooler waters in a
high-shear environment, and these factors are forecast to cause
Sebastien to transition into a non-convective low or extratropical
cyclone in 36-48 h. Careful watchers of the forecast will note that
NHC has predicted extratropical transition at 48 h since Sebastien
was born over 48 h ago, and this timing has been pushed back
primarily due to the slower-than-expected motion. Thus, this timing
can't be considered a particularly confident prediction until the
track forecast becomes more consistent.


FORECAST POSITIONS AND MAX WINDS

INIT 22/0300Z 24.7N 57.8W 50 KT 60 MPH
12H 22/1200Z 26.0N 55.5W 55 KT 65 MPH
24H 23/0000Z 28.0N 51.7W 55 KT 65 MPH
36H 23/1200Z 30.3N 47.7W 45 KT 50 MPH
48H 24/0000Z 32.7N 43.4W 40 KT 45 MPH...POST-TROP/EXTRATROP
72H 25/0000Z 37.5N 34.0W 35 KT 40 MPH...POST-TROP/EXTRATROP
96H 26/0000Z...DISSIPATED

$$
Forecaster Blake
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Re: ATL: SEBASTIEN - Tropical Storm

#82 Postby Sciencerocks » Fri Nov 22, 2019 4:47 am

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Re: ATL: SEBASTIEN - Tropical Storm

#83 Postby Sciencerocks » Fri Nov 22, 2019 4:48 am

970
WTNT45 KNHC 220834
TCDAT5

Tropical Storm Sebastien Discussion Number 12
NWS National Hurricane Center Miami FL AL202019
500 AM AST Fri Nov 22 2019

Sebastien has become less organized this morning. Strong
southwesterly vertical wind shear of about 40 kt and dry air have
caused the low-level center of the storm to become exposed to the
southwest of the main area of deep convection. The initial
intensity remains 50 kt, based on the earlier ASCAT data, but this
is a little above the latest Dvorak estimates and could be generous.

The center of Sebastien has turned more to the right than expected,
with the initial motion estimated to be 065/13 kt. The models have
changed significantly this cycle, and now show a much slower forward
motion to the northeast during the next few days. This change
appears to be connected to a more vertically shallow system that
moves in the lower-level flow. The NHC track forecast has been
adjusted considerably slower and a little to the right of the
previous one, but it still is faster than nearly all of the
typically reliable models. Future adjustments will likely be made
if the model trend continues.

It no longer appears that Sebastien will strengthen. In fact, all
of the intensity guidance now suggests that the storm will gradually
weaken during the next few days as Sebastien remains in strong wind
shear conditions and moves over progressively cooler waters. In
addition, the model guidance has finally come into agreement that
Sebastien will not merge with the nearby cold front. Instead, the
cyclone is expected to move ahead of the weakening front and become
a non-convective post-tropical cyclone in about 2 days, or less,
when it moves over SSTs below 22 C. As mentioned in the previous
discussion, NHC and the models have had a challenging time figuring
out when Sebastien would lose its tropical characteristics, and we
have held the transition timing steady at 48 hours for a while.
Although there is still uncertainty, the models are in better
agreement in the timing of this transition. This intensity forecast
is a little lower than the previous one to come into better
agreement with the latest models.


FORECAST POSITIONS AND MAX WINDS

INIT 22/0900Z 24.8N 57.0W 50 KT 60 MPH
12H 22/1800Z 26.0N 54.3W 50 KT 60 MPH
24H 23/0600Z 27.2N 51.7W 45 KT 50 MPH
36H 23/1800Z 28.7N 49.1W 40 KT 45 MPH
48H 24/0600Z 30.0N 46.2W 35 KT 40 MPH...POST-TROPICAL
72H 25/0600Z 33.3N 38.4W 25 KT 30 MPH...POST-TROP/REMNT LOW
96H 26/0600Z...DISSIPATED

$$
Forecaster Cangialosi
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Re: ATL: SEBASTIEN - Tropical Storm

#84 Postby 1900hurricane » Fri Nov 22, 2019 8:01 am

SMAP hit Sebastien yesterday at 2156Z, back when it looked halfway decent, and was worth about 55 kt 1 minute sustained winds. That looks like a reasonable peak intensity estimate unless it does something weird while transitioning.

AL, 20, 201911212156, 30, SMAP, IR, , 2430N, 5860W, , 1, 48, 1, , , , 34, NEQ, 0, 0, 60, 64, , , , , 1, 0, , L, NASA, RSS, , , , , , , , , , , , , , , , , , , , , , , , , , , , 1, max. wind is 10 minute sustained
AL, 20, 201911212156, 30, SMAP, IR, , 2430N, 5860W, , 1, 48, 1, , , , 50, NEQ, 0, 0, 0, 0, , , , , 1, 0, , L, NASA, RSS, , , , , , , , , , , , , , , , , , , , , , , , , , , , 1, max. wind is 10 minute sustained
AL, 20, 201911212156, 30, SMAP, IR, , 2430N, 5860W, , 1, 48, 1, , , , 64, NEQ, 0, 0, 0, 0, , , , , 1, 0, , L, NASA, RSS, , , , , , , , , , , , , , , , , , , , , , , , , , , , 1, max. wind is 10 minute sustained


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Re: ATL: SEBASTIEN - Tropical Storm

#85 Postby Sciencerocks » Fri Nov 22, 2019 10:42 am

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Re: ATL: SEBASTIEN - Tropical Storm

#86 Postby sponger » Fri Nov 22, 2019 11:51 am

Is the grand Solar Minimum having an impact on hurricanes? It certainly appears to be.
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Re: ATL: SEBASTIEN - Tropical Storm

#87 Postby tolakram » Fri Nov 22, 2019 1:20 pm

sponger wrote:Is the grand Solar Minimum having an impact on hurricanes? It certainly appears to be.


I think this one is all about November. I haven't seen any research that shows a relationship between the solar activity and hurricane activity, has anyone else?
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Re: ATL: SEBASTIEN - Tropical Storm

#88 Postby xironman » Fri Nov 22, 2019 1:50 pm

tolakram wrote:
sponger wrote:Is the grand Solar Minimum having an impact on hurricanes? It certainly appears to be.


I think this one is all about November. I haven't seen any research that shows a relationship between the solar activity and hurricane activity, has anyone else?


Nope
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Re: ATL: SEBASTIEN - Tropical Storm

#89 Postby Sciencerocks » Fri Nov 22, 2019 3:42 pm

000
WTNT45 KNHC 222032
TCDAT5

Tropical Storm Sebastien Discussion Number 14
NWS National Hurricane Center Miami FL AL202019
500 PM AST Fri Nov 22 2019

Sebastien's structure has not changed since this morning. ASCAT data
that arrived just after the issuance of the previous advisory showed
that the system was producing winds slightly above 45 kt, a little
higher than the previous estimate. Since the structure of the
tropical storm has not changed since the time of the ASCAT, the
intensity has been set at 50 kt. It should be noted that this is
merely an adjustment of the intensity assessment and is not an
indication of strengthening.

The agreement between the intensity models is remarkably poor. In
just the first 24 h of the forecast, the solutions range from
dissipation (HMON), to hurricane-strength (HWRF), to steady-state
(most of the global models). Since the shear is high and SSTs ahead
of the cyclone will be fairly cold, the solution that makes the
most sense to me is that of the global and statistical-dynamical
models, which generally show slow weakening during the next couple
of days. Dissipation is still expected within 72 h.

The Jekyll and Hyde behavior of the models isn't limited to the
intensity forecast. While it seems clear that Sebastien will move
east-northeastward or northeastward along the southern end of a
frontal boundary during the next couple of days, the speed at which
it will move is very unclear. The deeper the cyclone remains, the
more influence strong upper-level southwesterly winds will have on
its track, and the faster it will likely move. The latest track
guidance unanimously shows a dramatically faster forward motion of
Sebastien. In fact, the consensus now shows a forward speed nearly
twice as fast as the previous NHC advisory. The official forecast
continues to chase the models but has not been moved nearly as far
as HCCA or TVCN. Confidence in the track forecast is quite low.

FORECAST POSITIONS AND MAX WINDS

INIT 22/2100Z 26.2N 53.7W 50 KT 60 MPH
12H 23/0600Z 27.3N 51.8W 50 KT 60 MPH
24H 23/1800Z 28.9N 49.2W 45 KT 50 MPH
36H 24/0600Z 31.0N 45.8W 45 KT 50 MPH
48H 24/1800Z 33.1N 41.5W 40 KT 45 MPH
72H 25/1800Z...DISSIPATED

$$
Forecaster Zelinsky
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Re: ATL: SEBASTIEN - Tropical Storm

#90 Postby MarioProtVI » Fri Nov 22, 2019 4:00 pm

NHC seems to be getting tired of Sebastien based on the last advisory header :lol:
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Re: ATL: SEBASTIEN - Tropical Storm

#91 Postby AnnularCane » Fri Nov 22, 2019 5:37 pm

:uarrow:

Already? Sebastien hasn't been around THAT long. :lol:
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Re: ATL: SEBASTIEN - Tropical Storm

#92 Postby 1900hurricane » Fri Nov 22, 2019 6:11 pm

Well, all NHC has done in the best track file for the past two days is more or less copy and paste with updates to position and some tweaks to wind radii. Can't really blame them! : P

AL, 20, 2019112100, , BEST, 0, 219N, 617W, 50, 999, TS, 34, NEQ, 100, 140, 0, 0, 1010, 150, 40, 60, 0, L, 0, , 0, 0, SEBASTIEN, M, 12, NEQ, 240, 150, 0, 120, genesis-num, 041,
AL, 20, 2019112100, , BEST, 0, 219N, 617W, 50, 999, TS, 50, NEQ, 0, 40, 0, 0, 1010, 150, 40, 60, 0, L, 0, , 0, 0, SEBASTIEN, M, 12, NEQ, 240, 150, 0, 120, genesis-num, 041,
AL, 20, 2019112106, , BEST, 0, 226N, 613W, 50, 999, TS, 34, NEQ, 100, 140, 0, 0, 1010, 150, 60, 60, 0, L, 0, , 0, 0, SEBASTIEN, M, 12, NEQ, 210, 150, 30, 120, genesis-num, 041,
AL, 20, 2019112106, , BEST, 0, 226N, 613W, 50, 999, TS, 50, NEQ, 0, 80, 0, 0, 1010, 150, 60, 60, 0, L, 0, , 0, 0, SEBASTIEN, M, 12, NEQ, 210, 150, 30, 120, genesis-num, 041,
AL, 20, 2019112112, , BEST, 0, 231N, 608W, 50, 999, TS, 34, NEQ, 100, 140, 0, 0, 1010, 150, 60, 60, 0, L, 0, , 0, 0, SEBASTIEN, M, 0, , 0, 0, 0, 0, genesis-num, 041,
AL, 20, 2019112112, , BEST, 0, 231N, 608W, 50, 999, TS, 50, NEQ, 0, 80, 0, 0, 1010, 150, 60, 60, 0, L, 0, , 0, 0, SEBASTIEN, M, 0, , 0, 0, 0, 0, genesis-num, 041,
AL, 20, 2019112118, , BEST, 0, 235N, 601W, 50, 999, TS, 34, NEQ, 100, 140, 0, 0, 1010, 150, 60, 60, 0, L, 0, , 0, 0, SEBASTIEN, M, 12, NEQ, 210, 150, 60, 120, genesis-num, 041,
AL, 20, 2019112118, , BEST, 0, 235N, 601W, 50, 999, TS, 50, NEQ, 0, 80, 0, 0, 1010, 150, 60, 60, 0, L, 0, , 0, 0, SEBASTIEN, M, 12, NEQ, 210, 150, 60, 120, genesis-num, 041,
AL, 20, 2019112200, , BEST, 0, 243N, 586W, 50, 999, TS, 34, NEQ, 120, 140, 50, 70, 1010, 150, 60, 60, 0, L, 0, , 0, 0, SEBASTIEN, M, 12, NEQ, 180, 180, 60, 120, genesis-num, 041,
AL, 20, 2019112200, , BEST, 0, 243N, 586W, 50, 999, TS, 50, NEQ, 0, 60, 0, 0, 1010, 150, 60, 60, 0, L, 0, , 0, 0, SEBASTIEN, M, 12, NEQ, 180, 180, 60, 120, genesis-num, 041,
AL, 20, 2019112206, , BEST, 0, 246N, 573W, 50, 999, TS, 34, NEQ, 120, 140, 50, 70, 1010, 200, 60, 60, 0, L, 0, , 0, 0, SEBASTIEN, M, 12, NEQ, 180, 180, 60, 120, genesis-num, 041,
AL, 20, 2019112206, , BEST, 0, 246N, 573W, 50, 999, TS, 50, NEQ, 0, 60, 0, 0, 1010, 200, 60, 60, 0, L, 0, , 0, 0, SEBASTIEN, M, 12, NEQ, 180, 180, 60, 120, genesis-num, 041,
AL, 20, 2019112212, , BEST, 0, 250N, 559W, 50, 999, TS, 34, NEQ, 120, 140, 50, 70, 1010, 200, 60, 60, 0, L, 0, , 0, 0, SEBASTIEN, M, 12, NEQ, 180, 150, 120, 150, genesis-num, 041,
AL, 20, 2019112212, , BEST, 0, 250N, 559W, 50, 999, TS, 50, NEQ, 0, 60, 0, 0, 1010, 200, 60, 60, 0, L, 0, , 0, 0, SEBASTIEN, M, 12, NEQ, 180, 150, 120, 150, genesis-num, 041,
AL, 20, 2019112218, , BEST, 0, 258N, 544W, 50, 999, TS, 34, NEQ, 170, 140, 50, 100, 1010, 200, 30, 60, 0, L, 0, , 0, 0, SEBASTIEN, M, 12, NEQ, 150, 150, 90, 180, genesis-num, 041,
AL, 20, 2019112218, , BEST, 0, 258N, 544W, 50, 999, TS, 50, NEQ, 0, 30, 0, 0, 1010, 200, 30, 60, 0, L, 0, , 0, 0, SEBASTIEN, M, 12, NEQ, 150, 150, 90, 180, genesis-num, 041,
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Re: ATL: SEBASTIEN - Tropical Storm

#93 Postby johngaltfla » Fri Nov 22, 2019 7:21 pm

sponger wrote:Is the grand Solar Minimum having an impact on hurricanes? It certainly appears to be.


WE are a long way from a GSM. It's low, but not nearly as bad as it will get should the theories and historical data verify.
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Re: ATL: SEBASTIEN - Tropical Storm

#94 Postby johngaltfla » Fri Nov 22, 2019 7:23 pm

tolakram wrote:
sponger wrote:Is the grand Solar Minimum having an impact on hurricanes? It certainly appears to be.


I think this one is all about November. I haven't seen any research that shows a relationship between the solar activity and hurricane activity, has anyone else?


There is no long term data since the last serous Grand Solar Minimum happened before records were kept.

IMHO, speaking from a theoretical perspective, I would expect an increase in activity, however much further south and closer to the equator should we enter into such a period.

Another debate, for another thread.

This storm, named after my school's mascot however, is quite impressive this late in the season. I honestly thought he would dissipate by now.
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Re: ATL: SEBASTIEN - Tropical Storm

#95 Postby EquusStorm » Fri Nov 22, 2019 8:07 pm

One of the discussions mentioned that on every advisory they were having to bump up post-tropical transition a little so that it was always 48 hours out and now apparently they expect it to remain distinct and just dissipate... very interesting little storm.
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Re: ATL: SEBASTIEN - Tropical Storm

#96 Postby DioBrando » Fri Nov 22, 2019 9:52 pm

LOL

"There is not much that I can add that my predecessors have not
already addressed except to say that Sebastien does not know that
is November near Thanksgiving."

"TENACIOUS SEBASTIEN DOES NOT KNOW IS NOVEMBER AND REFUSES TO WEAKEN"
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Re: ATL: SEBASTIEN - Tropical Storm

#97 Postby Sciencerocks » Fri Nov 22, 2019 9:58 pm

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Re: ATL: SEBASTIEN - Tropical Storm

#98 Postby Sciencerocks » Fri Nov 22, 2019 10:00 pm

000
WTNT45 KNHC 230237
TCDAT5

Tropical Storm Sebastien Discussion Number 15
NWS National Hurricane Center Miami FL AL202019
1100 PM AST Fri Nov 22 2019

There is not much that I can add that my predecessors have not
already addressed except to say that Sebastien does not know that
is November near Thanksgiving.

One interesting aspect tonight is that although the cloud pattern
has not change at all today with the low-level center on the
southern edge of the convection due to shear, and with the same
Dvorak numbers, ASCAT data that just arrived showed numerous vectors
of 50 kt and a few near 55 kt. On this basis, the initial intensity
has been adjusted upward to 55 kt in this advisory.

Sebastien has to weaken since is heading toward a hostile
environment of increasing shear and cooler waters. It might not do
it tonight, but the weakening process must begin within the next 24
hours or so. Both the GFS and the ECMWF open up the circulation
beyond 48 hours, and with the hostile environment ahead, the NHC
forecast calls for gradual weakening and dissipation in 3 days.

The cyclone is moving toward the northeast of 055 degrees at 13 kt.
Sebastien is embedded within the mid-latitude westerly flow, and the
cyclone has nowhere to go but to continue moving northeastward
with increasing forward speed. Models vary in speed, but on average
they all suggest acceleration.

FORECAST POSITIONS AND MAX WINDS

INIT 23/0300Z 27.0N 52.2W 55 KT 65 MPH
12H 23/1200Z 28.2N 50.2W 55 KT 65 MPH
24H 24/0000Z 30.5N 46.5W 45 KT 50 MPH
36H 24/1200Z 32.6N 42.5W 40 KT 45 MPH
48H 25/0000Z 35.5N 36.0W 35 KT 40 MPH
72H 26/0000Z...DISSIPATED

$$
Forecaster Avila
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Re: ATL: SEBASTIEN - Tropical Storm

#99 Postby Sciencerocks » Sat Nov 23, 2019 4:12 am

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Re: ATL: SEBASTIEN - Tropical Storm

#100 Postby TallyTracker » Sat Nov 23, 2019 8:05 am

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