ATL: ARLENE - Post-Tropical - Discussion

[W8NC4TX]

Does all this pre-season activity give us any reason to suspect a more active season than previously indicated? Or would these little blips of oddness be considered cool anomalies but of no real concern or consequence to anyone?

[Kazmit]

Does all this pre-season activity give us any reason to suspect a more active season than previously indicated? Or would these little blips of oddness be considered cool anomalies but of no real concern or consequence to anyone?

Not necessarily, but it could indicate a front loaded season, especially if El Niño develops in the fall. Personally, I think this season will be more active than expected (near normal), but that's just my opinion.

[Alyono]

I can see why Joe is complaining because there have been systems near the US coast that could easily be named but weren't.

However, the SST argument is a poor one. If it's a cyclone with a well-defined low, with no fronts attached, and is developing convection due to heat fluxes from the ocean, then it has met the definition of a (sub)tropical low. 21°C SSTs can produce enough instability if the middle atmosphere is cold enough.

JB is once again using junk science. A meteorologist should know it is not SSTs that allow for genesis and intensification, but the difference between the SST and the tropopause temperature

[wxman57]

Looks like STD One is on its way out now. Convection is fading. An approaching front will absorb it tomorrow.

[TropicalAnalystwx13]

Nice to see they designated Subtropical Depression One. We'll cut them some slack that it should have been done 24 hours sooner--post-season fix hopefully. After looking ragged earlier, convection is on the increase near and north of the center this evening. Probably not enough to boost the cyclone to Arlene though.

Re: earlier discussion, pre-season activity has little correlation to overall seasonal activity.

[AJC3]

I can see why Joe is complaining because there have been systems near the US coast that could easily be named but weren't.

However, the SST argument is a poor one. If it's a cyclone with a well-defined low, with no fronts attached, and is developing convection due to heat fluxes from the ocean, then it has met the definition of a (sub)tropical low. 21°C SSTs can produce enough instability if the middle atmosphere is cold enough.

JB is once again using junk science. A meteorologist should know it is not SSTs that allow for genesis and intensification, but the difference between the SST and the tropopause temperature

This tweet makes that painfully obvious...

 https://twitter.com/BigJoeBastardi/status/854686888174788608




His second point (the cold ULL) pretty much renders first point (about lower SSTs) null and void in this case. Colder mid to upper level temperatures (AOA 500MB) are what makes the existence and maintenance of subtropical and tropical cyclones (including "Medcanes") thermodynamically possible over the lower SSTs at high latitudes. There have been many, many discussions about this fact in S2K threads.

[RL3AO]

Look at the forecast sounding from the GFS.



The lifted index is only about -5°C. It's the cold mid-troposphere making the atmosphere unstable.

[Kazmit]

It may have already peaked, SAT appearance doesn't look as healthy as this morning. I doubt any strengthening has occurred, but we'll see in the coming update. Who knows, maybe it will be upgraded to a subtropical storm in post-analysis.

[weathaguyry]

It may have already peaked, SAT appearance doesn't look as healthy as this morning. I doubt any strengthening has occurred, but we'll see in the coming update. Who knows, maybe it will be upgraded to a subtropical storm in post-analysis.

Well there is a blossoming area of convection to the NE of the center, so maybe if that continues to blossom the way it is, and if the depression can maintain a tight circulation, maybe it will be named Arlene at 11PM.

[AJC3]

 https://twitter.com/BigJoeBastardi/status/854686888174788608




His second point (the cold ULL) pretty much renders first point (about lower SSTs) null and void in this case. Colder mid to upper level temperatures (AOA 500MB) are what makes the existence and maintenance of subtropical and tropical cyclones (including "Medcanes") thermodynamically possible over the lower SSTs at high latitudes. There have been many, many discussions about this fact in S2K threads.

Sigh...

 https://twitter.com/BigJoeBastardi/status/854804982700417024

[Kazmit]

It may have already peaked, SAT appearance doesn't look as healthy as this morning. I doubt any strengthening has occurred, but we'll see in the coming update. Who knows, maybe it will be upgraded to a subtropical storm in post-analysis.

Well there is a blossoming area of convection to the NE of the center, so maybe if that continues to blossom the way it is, and if the depression can maintain a tight circulation, maybe it will be named Arlene at 11PM.

We can hope! Although it would be a named storm for less than a day before it is absorbed by the incoming front.

[Hammy]

Absent of data conclusively showing the contrary, I think the convective intensity and how close it is to the center should warrant an upgrade at 11pm. Whether they'll actually upgrade or not though is another story, but it certainly looks like it's at storm intensity at the moment.

[Alyono]

I can see why Joe is complaining because there have been systems near the US coast that could easily be named but weren't.

However, the SST argument is a poor one. If it's a cyclone with a well-defined low, with no fronts attached, and is developing convection due to heat fluxes from the ocean, then it has met the definition of a (sub)tropical low. 21°C SSTs can produce enough instability if the middle atmosphere is cold enough.

JB is once again using junk science. A meteorologist should know it is not SSTs that allow for genesis and intensification, but the difference between the SST and the tropopause temperature

This tweet makes that painfully obvious...

 https://twitter.com/BigJoeBastardi/status/854686888174788608




His second point (the cold ULL) pretty much renders first point (about lower SSTs) null and void in this case. Colder mid to upper level temperatures (AOA 500MB) are what makes the existence and maintenance of subtropical and tropical cyclones (including "Medcanes") thermodynamically possible over the lower SSTs at high latitudes. There have been many, many discussions about this fact in S2K threads.

To see him make mistakes like this leads me to question his credentials. He is failing basic thermodynamics by his lack of understanding of instability

[cycloneye]

00z Best Track remains as SD.

AL, 01, 2017042000, , BEST, 0, 328N, 395W, 30, 996, SD

[Hammy]

00z Best Track remains as SD.

AL, 01, 2017042000, , BEST, 0, 328N, 395W, 30, 996, SD

No chance of upgrade then?


Edit: is anyone else having trouble with NRL's site?

[TheAustinMan]

Edit: is anyone else having trouble with NRL's site?

I'm having some problems as well. One alternative is the FNMOC page (https://www.fnmoc.navy.mil/tcweb/cgi-bin/tc_home.cgi?), though you'll have the bypass the secure connection warning. The FNMOC page functions very similarly to the NRL site.

The small blob of convection proximate to the circulation is doing a nice job trying to wrap around and over the LLC.

[weathaguyry]

I agree, it would be nice to know what kind of wind there is inside that blob, could they possibly be high enough to make the NHC upgrade to Subtropical Storm Arlene? We shall see...

[TheStormExpert]

Any new ASCAT passes?

[TheAustinMan]

Any new ASCAT passes?

This would be the very latest.

FNMOC

[cycloneye]

Subtropical Depression One Discussion Number 3
NWS National Hurricane Center Miami FL AL012017
1100 PM AST Wed Apr 19 2017

The subtropical depression has changed little in strength since
formation occurred earlier today. Deep convection is confined to a
small area over the northwestern quadrant. A pair of recent ASCAT
passes indicated that the maximum winds are still near 30 kt. These
data also showed that the wind field of the system has contracted
since the earlier ASCAT passes this morning.

The cyclone has been moving northeastward at 10 kt during the past 6
to 12 hours. A large extratropical cyclone is approaching the
system from the west-northwest, and it should cause the depression
to turn northward and then northwestward overnight and on Thursday.
Little change in strength is likely before the system dissipates
due to cold water and continued moderate shear. The models are in
excellent agreement, and show the extratropical low absorbing
the subtropical depression, or its remnants, in a day or so.

FORECAST POSITIONS AND MAX WINDS

INIT 20/0300Z 33.2N 39.3W 30 KT 35 MPH
12H 20/1200Z 35.3N 39.9W 30 KT 35 MPH
24H 21/0000Z...DISSIPATED

$$
Forecaster Cangialosi