ATL: KARL - Post-Tropical - Discussion

[cycloneye]

]

[AutoPenalti]

Code: Select all

The initial motion is 300/12.  A low- to mid-level ridge should
steer the system west-northwestward and then westward during the
forecast period, with some decrease in forward speed after 36 hours
as the ridge weakens slightly.  The forecast track is near the
center of the guidance envelope and close to the various consensus
models.

Some strengthening is expected during the next 12-24 hours.  After
that, the cyclone is likely to encounter strong westerly vertical
wind shear while over sea surface temperatures of about 26C.  This
combination should lead to weakening, and the intensity forecast
shows the system weakening back to a depression by 36 hours.  Near
the end of the forecast period, the dynamical models diverge on the
evolution of the upper-level winds, with the ECMWF and UKMET
forecasting a more favorable pattern than the GFS. Based on this,
the forecast shows some re-intensification by 120 hours.  An
alternative scenario is that the cyclone degenerates to a tropical
wave as forecast by the GFS.  Overall, the intensity forecast is on
the low side of the guidance in best agreement with the LGEM.

I don't see any discussion about a fish happening. If it begins to weaken it will stay weak for sometime missing the trough to its north and the ridge could build back in.

[GlennOBX]

Am I missing something, or is the TWELVE models thread missing from the active board list? I could be wrong.

[SouthFLTropics]

Am I missing something, or is the TWELVE models thread missing from the active board list? I could be wrong.

It's there but it is still being shown as 95L

[cycloneye]

Am I missing something, or is the TWELVE models thread missing from the active board list? I could be wrong.

TWELVE Models Thread

[drezee]

12z GFS says hello to hebert's box

[BigB0882]

12Z models initialized as TD Twelve. Clearly a TD. The only land impacts will be the Cape Verde islands. Fish after that.

I am surprised at such a confident forecast so far out but coming from you I am sure you have very good reasons. Unless you were only talking about what the 12z models were showing and not making a prediction of your own.

[gatorcane]

12Z GFS is way west but weak.

[TheStormExpert]

12z GFS has been barely developing TD #12 for runs now which explains how it manages to get so far west.

I'm leaning towards a blend of the GFS and Euro with it recurving east of Bermuda.

[SFLcane]

12Z GFS is way west but weak.

Weak? Likelyhood of sinking air and shear ahead as most this season. Either way it's recurving

[abajan]

12Z models initialized as TD Twelve. Clearly a TD. The only land impacts will be the Cape Verde islands. Fish after that.

May I quote you on that? Oh wait ... I just did!

[setexholmes]

I'm not buying a recurve just yet. If Ike taught us anything it's that anything can happen. Around the same time of year too

[CycloneGuru]

I'm not buying a recurve just yet. If Ike taught us anything it's that anything can happen. Around the same time of year too

Im thinking the same. I was in bridge city when ike it, it was pretty bad

[wxmann_91]

I'm not buying a recurve just yet. If Ike taught us anything it's that anything can happen. Around the same time of year too

The blocking pattern that steered Ike way west was forecast well in advance. It's definitely outside normal climo but didn't just "happen".

There's nothing -- absolutely nothing to suggest that a remotely similar pattern will be in place for TD 12. The 0Z runs of the GFS and Euro were completely out of phase with regards to the 500mb pattern in 10 days -- the former had an east coast trough while the latter has a strengthening ridge in the exact same area.

The most likely scenario is that as long as TD 12 stays in the MDR, it will struggle. Longer range is a tossup, so best to go with the best technique we have: persistence. And that tells us that if it strengthens, it recurves; if it stays weak, it will be a sheared mess that may or may not become something down to road closer to the US.

[sma10]

All this talk of recurve, still too early. Is it likely to recurve? Yes, based on climatology and it's northern genesis, of course it is.

But far from certain at this point. Especially If Euro upper air pattern is correct at 10 days, it's not certain. Today's 12Z does show what looks like the beginning of recurve at 240hours, but it's really close.

[Kazmit]

I wouldn't be so sure about it being a fish. The Virgin Islands and the rest of the northern Leewards could be affected by this, as well as Bermuda and possibly Newfoundland. While it probably won't make landfall anywhere after leaving the Cabo Verde islands, it could still do something.

[setexholmes]

I know this doesn't belong in the model thread and this will be the last I post of it here.

I am in no way calling this another Ike, there have been plenty of invests and TDs gone this way this year to no avail, all I meant was that it was slightly eairy. As to your point WXMan after looking at Ike's old forum there was little to no climo to suggest a cruiser or a gulf hit. Most of it showed that it would recurve, even the models until it was further out in the Atlantic.

I can't steer enough though that I am not at all saying that this is what this one will do though.

[Emmett_Brown]

I agree that this is not a lock to recurve. Primarily because it could weaken and move west as a wave like many of the other invests this year.

[Kazmit]

I'm going with a track similar to what the GFS shows here, with the more "shallow" recurve. Except I hope it will become stronger than what they show here.

[cycloneye]

BULLETIN
TROPICAL DEPRESSION TWELVE ADVISORY NUMBER 2
NWS NATIONAL HURRICANE CENTER MIAMI FL AL122016
500 PM AST WED SEP 14 2016

...CENTER OF THE DEPRESSION NOW WEST OF THE CABO VERDE ISLANDS...


SUMMARY OF 500 PM AST...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...17.4N 26.5W
ABOUT 190 MI...310 KM WNW OF THE CABO VERDE ISLANDS
MAXIMUM SUSTAINED WINDS...35 MPH...55 KM/H
PRESENT MOVEMENT...WNW OR 295 DEGREES AT 15 MPH...24 KM/H
MINIMUM CENTRAL PRESSURE...1009 MB...29.80 INCHES


WATCHES AND WARNINGS
--------------------
There are no coastal watches or warnings in effect.


DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
At 500 PM AST (2100 UTC), the center of Tropical Depression Twelve
was located near latitude 17.4 North, longitude 26.5 West. The
depression is moving toward the west-northwest near 15 mph (24 km/h)
and a gradual turn toward the west is expected during the next
couple of days. On the forecast track, the center of the depression
should move away from the Cabo Verde Islands tonight and Thursday.

Maximum sustained winds are near 35 mph (55 km/h) with higher gusts.
Slight strengthening is expected during the next 24 hours, and the
depression could become a tropical storm tonight or on Thursday.
After that time, some weakening could occur as the cyclone
encounters unfavorable upper-level winds.

The estimated minimum central pressure is 1009 mb (29.80 inches).


HAZARDS AFFECTING LAND
----------------------
WIND: Gusty winds are possible over portions of the Cabo Verde
Islands through tonight.

RAINFALL: Locally heavy rains are expected over portions of the Cabo
Verde Islands through Thursday.


NEXT ADVISORY
-------------
Next complete advisory at 1100 PM AST.

$$
Forecaster Beven



TROPICAL DEPRESSION TWELVE DISCUSSION NUMBER 2
NWS NATIONAL HURRICANE CENTER MIAMI FL AL122016
500 PM AST WED SEP 14 2016

The depression has not become better organized since the last
advisory, with the most concentrated convection now in a cluster
just west of the estimated center position. The initial intensity
remains 30 kt in best agreement with a satellite intensity estimate
from SAB.

The initial motion is a somewhat uncertain 295/13 kt. A low- to
mid-level ridge should steer the system west-northwestward and then
westward during the forecast period, with some decrease in forward
speed after 36-48 hours as the ridge weakens slightly. The new
forecast track is similar to, but a little north of, the previous
track based on a slight northward shift in the track guidance.

Some strengthening is expected during the next 12 hours or so. After
that, the cyclone will encounter strong westerly vertical wind shear
caused by a developing upper-level trough near and north of the
cyclone. This, combined with passage over sea-surface temperatures
of about 26C-27C, should lead to weakening, and the intensity
forecast shows the system weakening back to a depression by 36
hours. Near the end of the forecast period, the dynamical models
continue to diverge on the evolution of the upper-level winds, with
the ECMWF and UKMET forecasting a more favorable ridge pattern near
the cyclone, whereas the GFS has an upper-level trough close by.
Based on these conflicting models, the forecast leans toward the
ECMWF/UKMET scenario and shows some re-intensification by 120 hours.
An alternative scenario is that the cyclone degenerates into a broad
low pressure area or tropical wave as forecast by the GFS. Overall,
the intensity forecast remains on the low side of the guidance in
best agreement with the LGEM.

Gusty winds remain possible over the Cabo Verde Islands tonight,
whereas locally heavy rains will remain possible through Thursday.

FORECAST POSITIONS AND MAX WINDS

INIT 14/2100Z 17.4N 26.5W 30 KT 35 MPH
12H 15/0600Z 17.9N 28.4W 35 KT 40 MPH
24H 15/1800Z 18.0N 30.8W 35 KT 40 MPH
36H 16/0600Z 18.1N 33.2W 30 KT 35 MPH
48H 16/1800Z 18.1N 35.6W 30 KT 35 MPH
72H 17/1800Z 18.0N 39.5W 30 KT 35 MPH
96H 18/1800Z 17.5N 43.5W 35 KT 40 MPH
120H 19/1800Z 18.0N 47.5W 40 KT 45 MPH

$$
Forecaster Beven