ATL: FOUR - Remnants - Discussion

[TheStormExpert]

Time for Bones!

[Sciencerocks]

000
WTNT44 KNHC 070237
TCDAT4

Tropical Depression Four Discussion Number 5
NWS National Hurricane Center Miami FL AL042017
1100 PM AST Thu Jul 06 2017

The depression continues to be poorly organized this evening.
Recent scatterometer data indicate that the circulation is losing
definition, with the center in that data well to the southeast of
the remaining convection. A complication, though, is recent
observations from NOAA buoy 41041 that suggest the possibility of a
second center closer to the remaining convection and well to the
north of the center seen in the scatterometer data. The initial
intensity remains 25 kt based mainly on the scatterometer data. It
is possible that the system has already degenerated to an open wave,
but for now advisories will be maintained until visible imagery
becomes available Friday morning.

The depression should continue to lose organization due to
entrainment of dry air and developing southwesterly shear. The new
intensity forecast now calls for the system to degenerate to a
remnant low between 12 and 24 h and become a open wave after 72 h.
Both of these events could occur earlier than current forecast.
It should be noted that the UKMET model suggests the possibility
the system could regenerate near the end of the forecast period.
However, the other large-scale models do not yet support this
scenario.

A strong low- to mid-level ridge to the north of the cyclone should
steer it westward to west-northwestward until dissipation. The new
forecast track lies near the model consensus and is a little to the
south of the previous track.


FORECAST POSITIONS AND MAX WINDS

INIT 07/0300Z 13.4N 46.7W 25 KT 30 MPH
12H 07/1200Z 14.1N 49.6W 25 KT 30 MPH
24H 08/0000Z 15.2N 53.1W 25 KT 30 MPH...POST-TROP/REMNT LOW
36H 08/1200Z 16.6N 56.7W 25 KT 30 MPH...POST-TROP/REMNT LOW
48H 09/0000Z 18.3N 60.2W 20 KT 25 MPH...POST-TROP/REMNT LOW
72H 10/0000Z 21.0N 66.0W 20 KT 25 MPH...POST-TROP/REMNT LOW
96H 11/0000Z...DISSIPATED

$$
Forecaster Beven

LLC could be reforming north in the convection...Interesting.

[tarheelprogrammer]

0z Intensity models are hinting at regeneration. Yesterday very few if any showed the storm above 35 mph. Creeping back up maybe? SHIP seems to keep it where it is now, and then gradually builds it up. Hmmm.

[Aric Dunn]

Interesting..

[Hurricaneman]

This may need to be watched beyond day 3 for possible intensification if the models are right

[AutoPenalti]

Maybe that's why they haven't downgraded to a demand low?

[Blinhart]

I think the size of the system is actually helping itself, it can keep it's core circulation together even if SAL gets in there and gets rid of most of the storms, if it can get away from the SAL there is a good chance of it getting itself in real good situation and strengthen.

[Sciencerocks]

The 00z gfs is weaker compared to the 18z gfs...The 00z kept a low through 60-66 hours as it passed north of the islands, but the latest doesn't. I do agree with Bline on the possibility of this surviving the SAL/Shear and becoming something.

The azores/Bermuda ridge on the other hand holds all the way to at least 75 west through 144 hours at the 850 and 500 millibar level. So anything that survived and attempted to reform could be a close call or even a landfall. The Ukmet is very interested and shows what is possible with this system.

[Blinhart]

I think the size of the system is actually helping itself, it can keep it's core circulation together even if SAL gets in there and gets rid of most of the storms, if it can get away from the SAL there is a good chance of it getting itself in real good situation and strengthen.

And I have seen way worse systems called a TD, so I have no problem with this being called a TD, and if it still has the slightest chance of hitting the Antilles as a TS I rather it be as a TD than a PTC, I already ain't liking the PTC.

[Hammy]

ASCAT from earlier shows barely any circulation, but that was almost three hours before the most recent advisory. The buoy it seems to have passed almost directly over indicates otherwise though, having recorded winds from the north, west, and then south, indicating that the circulation has indeed redeveloped closer to the convection. Staring intently at cloud motion, and also based on the buoy, I've circled my position estimate.

[AtlanticWind]

ASCAT from earlier shows barely any circulation, but that was almost three hours before the most recent advisory. The buoy it seems to have passed almost directly over indicates otherwise though, having recorded winds from the north, west, and then south, indicating that the circulation has indeed redeveloped closer to the convection. Staring intently at cloud motion, and also based on the buoy, I've circled my position estimate.
http://i.imgur.com/aN31NeE.png

Seems very plausible, it would be interesting if this system survives the next few days if there is a chance of restrengthing
As it nears the coast of the US

[Sciencerocks]

07/0545 UTC 13.9N 47.2W T1.0/1.0 04L -- Atlantic

I agree with Hammy on her position close to the buoy...System is holding on.

[Sciencerocks]

ZCZC MIATCDAT4 ALL
TTAA00 KNHC DDHHMM

Tropical Depression Four Discussion Number 6
NWS National Hurricane Center Miami FL AL042017
500 AM AST Fri Jul 07 2017

The small, tenacious depression has continued to hold its own early
this morning with the low-level center now having moved up into the
deep convective cloud mass, with the center being north of the
previous advisory positions based on earlier scatterometer and buoy
wind data. Upper-level outflow is fair in all quadrants, albeit
elongated from northwest to southeast, and the vertical wind shear
has now shifted from northeasterly to light southwesterly at less
than 5 kt. The initial intensity is being maintained at 25 kt based
on 0600 UTC satellite classifications of 25 kt from TAFB and SAB,
but it wouldn't surprise me if the system isn't a little stronger
given the noticeable improvement in the convective cloud pattern
since the time of those fixes.

The initial motion estimate is 285/19 kt. The new NHC forecast track
has been shifted northward of the previous advisory track, but only
due to the more northward initial position. Otherwise, there is
little change to the previous forecast reasoning. A strong low- to
mid-level ridge to the north of the depression should act to steer
the small cyclone generally west-northwestward until dissipation
occurs in about 96 h. The new forecast track lies down the middle
of the tightly clustered model suite, near the consensus model TVCN.

The depression is expected to retain that status for another 36 h or
so while the vertical wind shear remains relatively low at less than
15 kt. By 36-48 h, westerly vertical wind shear is forecast to
increase to around 20 kt, which should induce gradual weakening. The
small cyclone is expected to degenerate into a remnant low by 48-72
h and dissipate by 96 h. There is one important caveat to note and
that is the UKMET model, which continues to show less weakening and
even strengthening in 96 and 120 h when the system is approaching
the Bahamas. Although the other global and regional models do not
show regeneration at this time, they do however show similar
improving upper-level wind conditions east of Florida by 120 h. For
now, the official intensity forecast remains similar to the previous
advisory and the consensus model IVCN through 48 h, after which the
forecast is lower than the intensity consensus.

FORECAST POSITIONS AND MAX WINDS

INIT 07/0900Z 15.0N 48.8W 25 KT 30 MPH
12H 07/1800Z 15.8N 51.6W 25 KT 30 MPH
24H 08/0600Z 17.1N 55.1W 25 KT 30 MPH
36H 08/1800Z 18.6N 58.7W 25 KT 30 MPH
48H 09/0600Z 20.1N 61.9W 20 KT 25 MPH...POST-TROP/REMNT LOW
72H 10/0600Z 22.8N 67.7W 20 KT 25 MPH...POST-TROP/REMNT LOW
96H 11/0600Z...DISSIPATED

$$
Forecaster Stewart

NNNN

[Nimbus]

The subtropical ridging is pushing west into the Caribbean and the TUTT low near -60 is lifting north a little this morning. Still some dry air west of TD4 so not looking for much intensification but in order for the UK model to verify TD 4 would need to maintain these periodic overnight convective bursts.

NHC is being more than patient about calling in the doctor..

[OuterBanker]

ZCZC MIATCDAT4 ALL
TTAA00 KNHC DDHHMM

Tropical Depression Four Discussion Number 6
NWS National Hurricane Center Miami FL AL042017
500 AM AST Fri Jul 07 2017

The small, tenacious depression has continued to hold its own early
this morning with the low-level center now having moved up into the
deep convective cloud mass, with the center being north of the
previous advisory positions based on earlier scatterometer and buoy
wind data. Upper-level outflow is fair in all quadrants, albeit
elongated from northwest to southeast, and the vertical wind shear
has now shifted from northeasterly to light southwesterly at less
than 5 kt. The initial intensity is being maintained at 25 kt based
on 0600 UTC satellite classifications of 25 kt from TAFB and SAB,
but it wouldn't surprise me if the system isn't a little stronger
given the noticeable improvement in the convective cloud pattern
since the time of those fixes.

The initial motion estimate is 285/19 kt. The new NHC forecast track
has been shifted northward of the previous advisory track, but only
due to the more northward initial position. Otherwise, there is
little change to the previous forecast reasoning. A strong low- to
mid-level ridge to the north of the depression should act to steer
the small cyclone generally west-northwestward until dissipation
occurs in about 96 h. The new forecast track lies down the middle
of the tightly clustered model suite, near the consensus model TVCN.

The depression is expected to retain that status for another 36 h or
so while the vertical wind shear remains relatively low at less than
15 kt. By 36-48 h, westerly vertical wind shear is forecast to
increase to around 20 kt, which should induce gradual weakening. The
small cyclone is expected to degenerate into a remnant low by 48-72
h and dissipate by 96 h. There is one important caveat to note and
that is the UKMET model, which continues to show less weakening and
even strengthening in 96 and 120 h when the system is approaching
the Bahamas. Although the other global and regional models do not
show regeneration at this time, they do however show similar
improving upper-level wind conditions east of Florida by 120 h. For
now, the official intensity forecast remains similar to the previous
advisory and the consensus model IVCN through 48 h, after which the
forecast is lower than the intensity consensus.

FORECAST POSITIONS AND MAX WINDS

INIT 07/0900Z 15.0N 48.8W 25 KT 30 MPH
12H 07/1800Z 15.8N 51.6W 25 KT 30 MPH
24H 08/0600Z 17.1N 55.1W 25 KT 30 MPH
36H 08/1800Z 18.6N 58.7W 25 KT 30 MPH
48H 09/0600Z 20.1N 61.9W 20 KT 25 MPH...POST-TROP/REMNT LOW
72H 10/0600Z 22.8N 67.7W 20 KT 25 MPH...POST-TROP/REMNT LOW
96H 11/0600Z...DISSIPATED

$$
Forecaster Stewart

NNNN

Of all the NHC forecasters Stacy Stewart is my favorite. It's always fun to read between the lines of his forecast. He mentioned the UKMET in his forecast and how it doesn't dissipate td4. It shows the respect he has for the model. I doubt that if the CMC showed the same he would even mention it.

[dexterlabio]

wow is there a record for the most number of days a system was just a TD?

[ronjon]

Anyone able to post the 00z UKMET run? It was mentioned in the NHC 5 am discussion.

[tolakram]

Anyone able to post the 00z UKMET run? It was mentioned in the NHC 5 am discussion.

You can see it here a few hours after it runs: https://ruc.noaa.gov/hfip/tcgen/

[GCANE]

If TD4 intensifies more than forecasted, it'll erode the NA Sub Trop High.
That in turn could steer the next wave, forecast to intensify thru the Carib, into more SM and into the GOM.

[wxman57]

Looks like it's a tropical wave, to me. Visible satellite is the classic wave look. Not much evidence of any circulation. Definitely would not qualify for an upgrade to a depression. Of course, it still needs to be monitored for potential development just like every other strong wave. Katrina was TD 10 out in the MDR. It weakened to a wave then became TD 12 and Katrina. I don't think this will become another Katrina, but we still need to keep an eye on it.