ATL: KARL - Post-Tropical - Discussion

[cycloneye]

TROPICAL DEPRESSION TWELVE DISCUSSION NUMBER 6
NWS NATIONAL HURRICANE CENTER MIAMI FL AL122016
500 PM AST THU SEP 15 2016

Deep convection has redeveloped in the northeastern quadrant of the
depression, although it is still a good distance away from the
center. Consequently, Dvorak classifications are just about the
same as earlier, and the initial wind speed estimate is kept at 30
kt. Southwesterly wind shear is expected to continue for a day or
two while the cyclone remains under the influence of an upper-level
trough. This trough is then expected to be replaced by a ridge in a
couple of days, with generally lighter shear by early next week.
While some weakening is still forecast, model guidance is in better
agreement on the depression eventually reaching a more conducive
environment for restrengthening, and the official intensity forecast
is raised a bit in the long term. This forecast could be
conservative for next week if the rather conducive environments
forecast by the ECMWF and UKMET models materialize.

The cyclone continues moving westward at 11 kt, and a west or
west-southwest motion is expected for the next few days while the
depression moves around a strengthening Atlantic subtropical ridge.
Thereafter, a turn to the west-northwest is forecast due to the
system reaching the southwestern periphery of the ridge. The model
guidance has spread out some on this cycle, with the UKMET having
shifted a fair distance north of its previous run. A stronger
system would probably turn a bit more to the west-northwest given
the forecast upper-level southeasterly winds. Since the intensity
prediction is higher than the last one, it makes sense to show the
cyclone gaining some latitude by the end of the forecast period. The
new NHC forecast is adjusted to the north of the previous one, but
still lies on the southern side of the guidance envelope.

FORECAST POSITIONS AND MAX WINDS

INIT 15/2100Z 17.8N 31.4W 30 KT 35 MPH
12H 16/0600Z 17.9N 33.3W 30 KT 35 MPH
24H 16/1800Z 18.0N 36.0W 30 KT 35 MPH
36H 17/0600Z 17.8N 38.6W 25 KT 30 MPH
48H 17/1800Z 17.5N 41.2W 30 KT 35 MPH
72H 18/1800Z 17.0N 46.5W 35 KT 40 MPH
96H 19/1800Z 17.5N 51.5W 40 KT 45 MPH
120H 20/1800Z 18.5N 56.0W 45 KT 50 MPH

$$
Forecaster Blake

[cycloneye]

The model
guidance has spread out some on this cycle, with the UKMET having
shifted a fair distance north of its previous run. A stronger
system would probably turn a bit more to the west-northwest given
the forecast upper-level southeasterly winds. Since the intensity
prediction is higher than the last one, it makes sense to show the
cyclone gaining some latitude by the end of the forecast period. The
new NHC forecast is adjusted to the north of the previous one, but
still lies on the southern side of the guidance envelope

[PTrackerLA]

Amazing how quickly some take a day 10 upper air forecast as fact lol. While I think a recurve is ALWAYS the most likely scenario I wouldn't totally write this off yet. There's a very long ways to go and if said trough is delayed by 36-48 hours on the 12z Euro the EC would be under the gun. It's happened before (Gloria).

Edit: Looks like several members of the 12z Euro ensembles bring TD 12 to the east coast and even one into the gulf. Much more bullish on the western end versus 00z.

[fci]

They are tracking this through the #1 Hebert Box which puts an evil hex on Florida.

I don't have statistics but I would venture to say that the percentage of systems in the Hebert Box that actually affect Florida is extremely low.
Plus the Hebert Box refers to HURRICANES passing through the box, not Tropical Depressions.

[cajungal]

It is rare that any wave off Africa would make it all the way across the basin and esp get in the gulf mid to late September. Usually this time of the year troughs start coming down and recurves it.

[curtadams]

I'd side with the GFS on this one with the way the season is going so far, nothing more than a weakening tropical depression from here on out.

Me too. It's still got to go through the MDR (main degeneration region). In general the models have been too bullish on storms there this year, although usually it's been the GFS that's been the worst (other than the CMC, and sometimes not even that).

[SFLcane]

Were talking the same Euro that has been very overly bullish with every wave that leaves Africa this season, right?

Yep lol.. Models have been horrific as far as Iam concerned. GFS showing no development bets 00z euro is much weaker. The Atlantic " land of the naked swirls " is just to hostile right now to really buy into any one model in my view you might wanna sit back and pull up a WV loop and yep that ain't gonna happen. Still cleaning up from hermine here in SFL. Just horrible

[tolakram]

12z euro run. My take is we won't have any decent idea until 5 days or less from any landfall. Is the GFS correctly identifying poor conditions again, or is it missing a larger pattern change. I think the odds really are about 50/50, very hard to know.

[JaxGator]

It is rare that any wave off Africa would make it all the way across the basin and esp get in the gulf mid to late September. Usually this time of the year troughs start coming down and recurves it.

Hugo and Jeanne are two big examples of TWs and becoming hurricanes making across the basin this time of year and hitting land. Hope this doesn't repeat those monsters.

[Cunxi Huang]

Again, Euro 940 mb and GFS shows nothing

[centuryv58]

12z euro run. My take is we won't have any decent idea until 5 days or less from any landfall. Is the GFS correctly identifying poor conditions again, or is it missing a larger pattern change. I think the odds really are about 50/50, very hard to know.

Your assessment makes the most sense. Some here put too much stock in one model run and assume that is the final word.

[Blown Away]

Late September heavily favors a recurve system if it moves N of the Caribbean... Bermuda/Canada always a chance...

[cycloneye]

 https://twitter.com/RaleighWx/status/776533171135401984




 https://twitter.com/EricBlake12/status/776538684812304386

[ConvergenceZone]

Even in super active seasons(like 2005), these are usually still recurves when they form this far out.

[Kazmit]

They are tracking this through the #1 Hebert Box which puts an evil hex on Florida.

I don't have statistics but I would venture to say that the percentage of systems in the Hebert Box that actually affect Florida is extremely low.
Plus the Hebert Box refers to HURRICANES passing through the box, not Tropical Depressions.

Very true, a path through the Hebert Box doesn't usually determine whether or not it hits Florida. It depends on a number of factors, and usually a weaker storm like this would not fit into the conclusion that many hurricanes that have passed through here affect Florida. In addition, this looks like it will probably be more likely to recurve and not affect the US, as stated in the latest discussion.

[AutoPenalti]

I'm still not seeing a recurve. It's too far out to say where this is going.

[cycloneye]

 https://twitter.com/EricBlake12/status/776543703712329728

[Kazmit]

Late September heavily favors a recurve system if it moves N of the Caribbean... Bermuda/Canada always a chance...

Very true. Steering winds usually drive storms out to sea once they pass north of the Lesser Antilles. Paths like the one 99L/Hermine took are becoming less likely at this time of year.

[abajan]

https://twitter.com/EricBlake12/status/776543703712329728

Oh my! If convection continues to build like that overnight, by the time D-MAX rolls around it'll be off the charts:

[Cunxi Huang]

spread spread spread...may have sig development after +72h. can't tell right now