ATL: INVEST 92L - Discussion

[kevin]

92L right now. New recon data in, the center has 4 kt FL winds and even the weaker northern side now has 37 kt SFMR and 32 kt FL winds.

[BobHarlem]

recon
 https://twitter.com/cfhc/status/1804183367602037131

[zhukm29]

92L right now. New recon data in, the center has 4 kt FL winds and even the weaker northern side now has 37 kt SFMR and 32 kt FL winds.

Basically Bertha/Danny 2.0, similar location and surprise formation as well. And if those seasons are any indication of what is to come…

[MetroMike]

On true color satellite one can see the naked swirl becoming more mis-aligned with the convection. They were correct to not upgrade this.

[cycloneye]

 https://x.com/FerragamoWx/status/1804181916150636610

[chaser1]

Please explain it it to me if I an misunderstanding something here. But with many 30+ kt SFMR & surface wind estimates (as well as multiple 35 kt+ measurements) & a clear center with plenty of convection near it, how is this not at the very least a TD? It doesn't matter how long the TC will still have before landfall, a TD designation should not be subjective based on impacts or the presence of prior advisories, but purely on whether a system matches the requirements and as far as I can see this one does. The NHC consists of experts in their field so I'm sure they're making the right call, I just don't fully understand it myself so if anyone could clarify.

Kevin, that's a very legit question. All of the points that you made are factors toward determining whether a TD or TS has in fact developed. The only reason that I think that 92L has not been designated as a TD is the lack of identified west winds at the surface. If I were correct that would explain NHC's possible perception of this system being an open (albeit very sharp) wave or trough of low pressure. On the other hand and to your point, NHC DID claim that a small well defined center of low pressure has developed. Well, what gives?? That statement suggests a "closed circulation" and clearly having some west wind component, right? So I see how that contradiction would cause you and others question the lack of any upgrade.

I'm still seeing a low level swirl that seems to be moving WNW to NW, while some level of westerly or northwestern mid to upper level shear clearly appears to be displacing any quasi CDO (or primary convection) off to the south. I don't know to what degree the slot of dry air over the Fla panhandle and eastern Georgia/Florida may be impacting this, but right now I certainly would have a hard time saying that 92L is looking like any well played Jinga game LOL.

All in all, I think better communication could have been applied here.

[LarryWx]

On true color satellite one can see the naked swirl becoming more mis-aligned with the convection. They were correct to not upgrade this.

Is this truly a “naked swirl” or would it be better described as having convection sheared to the south? Don’t naked swirls have no nearby convection?

[MarioProtVI]

Decoupling. Will be a naked swirl by tonight when it moves ashore. Good call by NHC

[Ubuntwo]

Decoupling. Will be a naked swirl by tonight when it moves ashore. Good call by NHC

A TC that only meets the criteria for a few hours is still a TC.

[LarryWx]

Decoupling. Will be a naked swirl by tonight when it moves ashore. Good call by NHC

But is this a tropical cyclone?

[chaser1]

92L compared to Bertha, Danny, (and COUNTLESS others)??
That could be viewed & debated two different ways.
1) Compared to past named tropical storms like Danny & Bertha, 92L should be tagged as a TS (or at least a TD).
2) Danny, Bertha (and countless others) should never have been upgraded and classified as named storms to begin with.

This has been a recurring 2-3 decades old debate inside & outside of this forum and a "Sticky note" link to that discussion thread would be good for someone to bump here. If such a thread hasn't been created, "What Defines A Tropical Depression/Storm" might be really good to establish.

[Sciencerocks]

[USTropics]

Please explain it it to me if I an misunderstanding something here. But with many 30+ kt SFMR & surface wind estimates (as well as multiple 35 kt+ measurements) & a clear center with plenty of convection near it, how is this not at the very least a TD? It doesn't matter how long the TC will still have before landfall, a TD designation should not be subjective based on impacts or the presence of prior advisories, but purely on whether a system matches the requirements and as far as I can see this one does. The NHC consists of experts in their field so I'm sure they're making the right call, I just don't fully understand it myself so if anyone could clarify.

Kevin, that's a very legit question. All of the points that you made are factors toward determining whether a TD or TS has in fact developed. The only reason that I think that 92L has not been designated as a TD is the lack of identified west winds at the surface. If I were correct that would explain NHC's possible perception of this system being an open (albeit very sharp) wave or trough of low pressure. On the other hand and to your point, NHC DID claim that a small well defined center of low pressure has developed. Well, what gives?? That statement suggests a "closed circulation" and clearly having some west wind component, right? So I see how that contradiction would cause you and others question the lack of any upgrade.

I'm still seeing a low level swirl that seems to be moving WNW to NW, while some level of westerly or northwestern mid to upper level shear clearly appears to be displacing any quasi CDO (or primary convection) off to the south. I don't know to what degree the slot of dry air over the Fla panhandle and eastern Georgia/Florida may be impacting this, but right now I certainly would have a hard time saying that 92L is looking like any well played Jinga game LOL.

All in all, I think better communication could have been applied here.

You both have hit on a lot of key points here, I think the main takeaway is it's a subjective process. The four main criteria for the NHC in designating a tropical cyclone is:

1. Must be a warm core system (check)
2. Must have a low-level circulation that is fully closed off (it did that this morning)
3. Must have surface winds of 35kt+ (recon confirmed)
4. Must have persistent convection (this is the subjective part for 92L, some will say it has sustained and fired convection over the past 24 hours, some may disagree)

All in all, I think the small footprint played a role in (1) the models not showing development and (2) one of the (subjective) reasons for the NHC not classifying this. I'm good with either option, but communication/transparency and consistency can definitely be improved upon.

[cycloneye]

The truth.

 https://x.com/hurricanetrack/status/1804187643669828084

[chaser1]

Decoupling. Will be a naked swirl by tonight when it moves ashore. Good call by NHC

A TC that only meets the criteria for a few hours is still a TC.

I totally disagree, but I respect your opinion. I'll gladly nominate you for Atlantic Basin Re-analysis Lead! Maybe a grant could be approved so that hundreds of easterly waves recorded during the satellite Era may be reanalyzed for having a few hours of apparant satellite evidence of a closed surface circulation. I recall many direct conversations with hurricane forecasters that explicitly would not classify/upgrade a disturbance to a TD or TS pending evidence of persistence. I don't specifically recall whether that equated to 12, 24, 36, or more hours, and that may clearly have been dictated by a lack of corroborating ship or buoy data as well. However, even with some corroborating evidence I recall a reluctance to pull the trigger in light of impending conditions expected to weaken the Invest. The topic is obviously a reasonable debate.

[Nuno]

 https://twitter.com/FloridaTropics1/status/1804184257545257383




I sure hope we never hear of people complaining about the NHC inflating numbers ever again

[cycloneye]

Southwestern Atlantic Ocean (AL92):
Satellite imagery and National Weather Service Doppler radar data
indicate that showers and thunderstorms associated with a
well-defined low pressure area centered about 80 miles
east-southeast of Brunswick, Georgia, continue to lack the necessary
organization for the low to be considered a tropical cyclone.
Recent Air Force Reserve reconnaissance aircraft data indicate that
winds to 35 mph are occurring in association with the low. Only a
small increase in the organization of the showers and thunderstorms
could result in the formation of a short-lived tropical depression
before it reaches the coast of northeastern Florida or Georgia
tonight, and interests there should monitor its progress. For more
information, refer to High Seas Forecasts issued by the National
Weather Service, as well as local forecasts issued by your local
National Weather Service Forecast Office.
* Formation chance through 48 hours...medium...60 percent.
* Formation chance through 7 days...medium...60 percent.

[psyclone]

It's nice to see a name not wasted for a change...although a naked swirl advisory for the GA coast would be nice:)

[Woofde]

Decoupling. Will be a naked swirl by tonight when it moves ashore. Good call by NHC

A TC that only meets the criteria for a few hours is still a TC.

I totally disagree, but I respect your opinion. I'll gladly nominate you for Atlantic Basin Re-analysis Lead! Maybe a grant could be approved so that hundreds of easterly waves recorded during the satellite Era may be reanalyzed for having a few hours of apparant satellite evidence of a closed surface circulation. I recall many direct conversations with hurricane forecasters that explicitly would not classify/upgrade a disturbance to a TD or TS pending evidence of persistence. I don't specifically recall whether that equated to 12, 24, 36, or more hours, and that may clearly have been dictated by a lack of corroborating ship or buoy data as well. However, even with some corroborating evidence I recall a reluctance to pull the trigger in light of impending conditions expected to weaken the Invest. The topic is obviously a reasonable debate.

I think the subjectivity of borderline tropical storms is a big reason why I'm against using named storm count as a main metric for activity. There are so many systems like this every year that could really go either way. What delineates a tropical storm from just a circulation is far more subjective than hurricane designation, for example.

Even had 92L been designated, it likely would've have only lasted 6 to 12 hours tops. From a basin perspective, that doesn't mean much in terms of favorabillity. If for example, we used named storm days as the main metric, I doubt there would be nearly as much discussion about wasted names and storms that should've been.

[USTropics]

It's nice to see a name not wasted for a change...although a naked swirl advisory for the GA coast would be nice:)

The Storm2k naked swirl advisory in effect for the northern Florida and southern Georgia coastline. Members in the area should immediately:

Ensure your car windows are rolled up. Secure any loose papers or mail in the yard. Get your naked swirl supplies in order (umbrella, candy, and popcorn). Conditions will begin to deteriorate decrease the temperature and bring a windy/cool evening to the area. Avoid Enjoy venturing outdoors and the subtle shift in wind regime.