ATL: INVEST 91L - Discussion

[Ivanhater]

Development chances near zero. Shear will be on the increase tomorrow. Won't be much left of it in 36-48 hrs.

I understand the hostile conditions coming, but why is this technically not considered a STS now? Winds of 40mpg with thunderstorms near the center, warm core, with a closed circulation? Had this been in the Gulf, it would be hard pressed not to get classified imo.

[AJC3]

Development chances near zero. Shear will be on the increase tomorrow. Won't be much left of it in 36-48 hrs.

I understand the hostile conditions coming, but why is this technically not considered a STS now? Winds of 40mph with thunderstorms near the center, warm core, with a closed circulation? Had this been in the Gulf, it would be hard pressed not to get classified imo.

A few reasons...

1) The vast majority of convective activity has been a direct result of strong divergence associated with the upper low, not the weak transient eddys that have been rotating around the broader surface circulation. By and large, there has been no warm core convective process going on with this system. Any increase in organization has been baroclinic.

2) I would probably take issue that there is any warm-core of depth/significance near the center of this low. With just about all the convection having been displaced downshear (to the north through east), the latent heat release needed for a significant warm-core type intensification or a transition is lacking. When you have dispaced latent heat release, what will generally happen is either 1) pressures will lower away from the center, not over it, or 2) the warm sector will stregthen, and before long you will have a ET (frontal) cyclone development or transition.

3) Crap SSTs, plus the weakening shear trend is about to reverse itself. You'll almost never see a marginal TD or STS start to be carried operationally when it looks to be not long for this world. The system is already being handled by OPC as an ET gale, so it's not like the wind/sea conditions aren't already being addressed.

[Ivanhater]

Thanks for the reply Tony.

It looks better tonight than I thought it would and wanted some technical reasons why it wasn't classified. You helped with that and more

It is curious though, the convection firing near the center with the feeder band extending to the south.

[WeatherGuesser]

Ivanhater, why are you posting images over 2Mb in file size? They can cause serious problems for people with slower connections or bandwidth limitations?

It would be much better if you would post links to those images and state the file size, so people could be warned how large they are.

HURAKAN also posts a number of oversize images in the 400-500Kb range.

[xironman]

Not half bad looking, but about to get crushed. You can clearly see a secondary eddy to the SW.

[wxman57]

Looks quite impressive. I think that if this system was impacting any land areas that it would be classified as a subtropical storm regardless of its structure. But since it's well out to sea, there's no good reason to upgrade it. NHC is in the business of protecting people, not seeing that every possible system in the basin is named. In any case, shear should be on the increase today/Saturday, which should strip the convection off to the east of the LLC.

[HURAKAN]

I think it's a case of study for possible upgrade after the season. I really never expected the system to look as good as it has been since yesterday.

[drezee]

Looks quite impressive. I think that if this system was impacting any land areas that it would be classified as a subtropical storm regardless of its structure. But since it's well out to sea, there's no good reason to upgrade it. NHC is in the business of protecting people, not seeing that every possible system in the basin is named. In any case, shear should be on the increase today/Saturday, which should strip the convection off to the east of the LLC.

Well at least they are consistent on this point, they only name borderline systems in the middle of the Atlantic later in the season...

[HURAKAN]

Another look at 91L

[HURAKAN]

SPECIAL TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
850 AM EDT FRI APR 22 2011

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

SHOWER ACTIVITY ASSOCIATED WITH A NON-TROPICAL LOW CENTERED ABOUT
385 MILES SOUTH-SOUTHEAST OF BERMUDA IS A LITTLE BETTER ORGANIZED
THIS MORNING...ALTHOUGH WINDS NEAR THE SYSTEM APPEAR TO HAVE
DECREASED BELOW GALE FORCE. THERE IS A LOW CHANCE...20 PERCENT...OF
THIS SYSTEM DEVELOPING INTO A SUBTROPICAL OR TROPICAL CYCLONE
WITHIN THE NEXT 12 TO 24 HOURS BEFORE ENVIRONMENTAL CONDITIONS
BECOME HIGHLY UNFAVORABLE FOR ADDITIONAL DEVELOPMENT. THE LOW IS
MOVING NORTHWARD AT 10 MPH BUT SHOULD SLOW DOWN LATER TODAY.
ADDITIONAL INFORMATION ON THIS LOW CAN BE FOUND IN HIGH SEAS
FORECASTS ISSUED BY THE NHC/TROPICAL ANALYSIS AND FORECAST
BRANCH...UNDER AWIPS HEADER NFDHSFAT2 AND WMO HEADER FZNT02 KNHC.
ADDITIONAL SPECIAL TROPICAL WEATHER OUTLOOKS WILL BE ISSUED AS
NECESSARY.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

$$
FORECASTER AVILA

[wxman57]

Twin lows rotating around a common center now:

[Lane]

Is it possible for one storm to "swallow" the other? Or could this be a formation of a "SuperStorm"?

[CrazyC83]

Looks like Arlene to me...

[plasticup]

Looks quite impressive. I think that if this system was impacting any land areas that it would be classified as a subtropical storm regardless of its structure. But since it's well out to sea, there's no good reason to upgrade it. NHC is in the business of protecting people, not seeing that every possible system in the basin is named. In any case, shear should be on the increase today/Saturday, which should strip the convection off to the east of the LLC.

If this was 2005 they would have classified it. They grabbed at flimsier straws that year.

[NDG]

Nearby buoy reporting pressure down to 1008mb with 13' waves.

[wxman57]

Is it possible for one storm to "swallow" the other? Or could this be a formation of a "SuperStorm"?

Smaller storms have been absorbed by larger storms in the past. In this case, it's just a couple of low-level swirls rotating counter-clockwise around a broad area of low pressure. That's quite common out in the tropics with sheared systems.

[tailgater]

Looks like it has deepen a bit but pressure gradient has weaken.
WV loop showing the wrapping up moisture with the dry slot to south and east.
http://mkwc.ifa.hawaii.edu/satellite/satanim.cgi?res=4km&banner=mkwc&chnl=wv&domain=bah&size=large&period=720&incr=30&rr=900&satplat=goeseast&overlay=off&animtype=flash

[HURAKAN]

205 TWD:

...SPECIAL FEATURE...

AT 1500 UTC...A 1008 MB LOW IS CENTERED ABOUT 510 NM NNE OF
PUERTO RICO AT 26.6N 63.6W WITH NEAR GALE FORCE WINDS N OF THE
CENTER. A SECONDARY SURFACE SWIRL IS LOCATED 100 NM SW OF THE
LOW CENTER NEAR 25.3N 64.7W INTERACTING WITH THE PRIMARY CENTER.
A SURFACE TROUGH EXTENDS S FROM THE LOW CENTER TOWARDS PUERTO
RICO ALONG 26N61W 23N61W 19N66W. WIDELY SCATTERED MODERATE
CONVECTION IN BANDS IS N OF THE CENTER FROM 26N-30N BETWEEN
60W-65W. A 1014 UTC WINDSAT PASS...AND A 1424 UTC ASCAT PASS
CONFIRM 30 KT WINDS N OF THE CENTER. AN UPPER LEVEL LOW IS
CENTERED DIRECTLY OVER THE SECONDARY SURFACE SWIRL. UPPER LEVEL
DRY AIR IS WRAPPING AROUND THE WESTERN AND SOUTHERN PORTIONS OF
THE SYSTEM. EXPECT THE SURFACE LOW CENTER TO TRACK SW TOWARDS
HISPANIOLA AND WEAKEN OVER THE NEXT 24-48 HOURS WITH CONVECTION
AND STRONGER WINDS N OF THE CENTER.

[SouthDadeFish]

So are they forecasting it to decouple? It looks like a subtropical storm to me... I guess it's "not worth" issuing advisories on since it will probably die soon? It appears to meet the criteria now as the circulation itself it firing off convection rather than being divergence forced, although divergence is definitely helping.

[wxman57]

I believe that the thinking is that once it loses its upper-level support (for convection) over the next few days that it will weaken and die out east of the Bahamas. For now, issuing advisories would not be any benefit to anyone, as it's not expected to impact any land areas.