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Non-Tropical Invest 90L continues producing gales east of the Bahamas #flhurricane.com
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Archives >> 2007 News Talkbacks

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Ed DunhamAdministrator
Meteorologist & CFHC Forum Moderator


Reged: Sun
Posts: 2565
Loc: Melbourne, FL
2550SM East of Central Florida
      #79652 - Sat Dec 29 2007 10:42 AM

Invest 95L in the east central Atlantic located at 27.2N 37.9W at 29/12Z and generally stationary. Winds listed at 25 knots (probably higher) and central pressure of 1008MB. System is attempting to transition to a hybrid subtropical cyclone from a cutoff upper level low that developed a surface low a couple of days ago (as first noted by HF).

Invest 95L

Forecast is for little movement for a day or two and then west southwest to southwest track and weakening as the system encounters increasing southwesterly shear ahead of a mostly upper level trough. SHIPS model anticipates TS/STS strength for a few days - probably already there, but transition toward a warm core or hybrid has only started in the upper levels and does not yet extend to the surface (and it may not make it, although SSTs started in the 22C-23C range a few days ago and low is now drifting close to 25C SSTs).

If it should get upgraded before Tuesday, the name would be Pablo. Probably the quietest busy season I've ever seen
ED

Edited by Ed Dunham (Sun Dec 30 2007 12:40 AM)


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allan
Weather Master


Reged: Thu
Posts: 468
Loc: Palm Coast, Florida 29.55N 81.20W
Re: 2550SM East of Central Florida [Re: Ed Dunham]
      #79654 - Sat Dec 29 2007 11:58 AM

We probably would have had a ton of storms if shear wasn't so harsh this year, I'd say about 18 storms with Karen and Irene making landfall somewhere on the East coast, there were no fronts that could turn them away at the time. We had high pressure blocking any recurvatures. Barry and Gabrielle could have been a Hurricane, Gabrielle could have been a record East Coast storm. Getting back this our Subtropical Storm, which by the T numbers of 2.5 which equals 40 mph I think, and by the convection completely now wrapping around the center, and last most of the frontal characteristics gone.. I think we already have a Subtropical Storm that most aren't recognizing just yet. I think they'll pull the trigger either tonight or tommorrow if organization can either hold, or get better.

--------------------
Allan Reed - 18,9,5


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HanKFranK
User


Reged: Mon
Posts: 1841
Loc: Graniteville, SC 33.56N 81.82W
95L [Re: Ed Dunham]
      #79655 - Sat Dec 29 2007 12:05 PM

i guess that gale center means business. it has quite an impressive structure on satellite--surprisingly rounded, and not very extratropical-looking. it has two cycles of ssd classifications as a subtropical storm... usually a stack of those will get something named. not nearly enough convection on it to start talking about it becoming a tropical storm, but it's starting to drift into the domain of subtropical status. most of the globals show it persisting at or near current strength through monday, which would definitely give it a window to get there. generic solution from a blend of globals is it hanging out there as a 1004-1010 mb low and completing a sort of hairpin or loop to the north, then diving wsw... all well out in the open atlantic. there is some high-level westerly shear (but not deep enough convection to get it shredded... maybe similar to those late 2005 systems that wandered out there with flatter vertical structure than classic deep-tropic systems), and eventually that will rip this little feature up as a deep layer trough plows into the western atlantic. that is the same trough that will be associated with the coldest air of the season driving into the southeast (looking for 15-20 here; you floridians may be in for a citrus-unfriendly sort of week).
an interesting sort of aside is that some sort of december tropical activity has occurred more often than not this decade. if we have a pablo pop up in the next (or somehow an arthur?), that will pad those peculiar numbers even more.
HF 1705z29december


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Rich B
British Meteorologist


Reged: Sat
Posts: 498
Loc: Gloucestershire, England, UK 51.81N 2.51W
Re: 2550SM East of Central Florida [Re: Ed Dunham]
      #79656 - Sat Dec 29 2007 01:56 PM

From the latest TWD:

...SPECIAL FEATURE...

INTERESTING FEATURE FOR THE DAY IS THE DEEP CYCLONE CENTERED
NEAR 27N38W. THIS SYSTEM HAS REMAINED STATIONARY FOR A COUPLE OF
DAYS AND ORGANIZED CONVECTION IS DEVELOPING IN A COUPLE OF BANDS
LOCATED TO THE EAST OF THE CENTER. QUIKSCAT WINDS SUGGEST THAT
THERE ARE SOME GALE FORCE WINDS ALONG THE NORTHERN SEMI-CIRCLE
AND SE QUADRANT OF THE SYSTEM...THAT SEEMS TO BE ACQUIRING SOME
SUBTROPICAL CHARACTERISTICS. THE MOST COMMON TYPE OF SUBTROPICAL
CYCLONE IS AN UPPER-LEVEL COLD LOW WITH CIRCULATION EXTENDING TO
THE SURFACE...AS IN THIS CASE. ACCORDING TO THE UW-CIMSS
PRODUCTS...VERTICAL SHEAR ON THE SYSTEM IS RELATIVELY WEAK...BUT
THIS LOW-MODERATE SHEAR ENVIRONMENT MAY ONLY LAST FOR ANOTHER
DAY OR SO BEFORE STRONG UPPER WESTERLIES IMPACT THE SYSTEM WITH
THE APPROACH OF A VIGOROUS SHORT-WAVE TROUGH. THE CYCLONE SHOULD
MEANDER IN PLACE FOR THE NEXT 24-36 HOURS OR SO. SOME OF THE
MODEL GUIDANCES MOVE THIS SYSTEM TO THE SW ACROSS THE OPEN OCEAN
WATERS. THIS SYSTEM COULD BECOME A SUBTROPICAL CYCLONE AT ANY
TIME.

--------------------
Rich B

SkyWarn UK


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cieldumort
Moderator


Reged: Mon
Posts: 1403
Loc: Austin, Tx 30.40N 97.80W
Re: 2550SM East of Central Florida [Re: Ed Dunham]
      #79657 - Sat Dec 29 2007 02:38 PM

A couple of things worth mentioning -

NRL hasn't been updating very well for all systems since Friday, so it's not just 95L not being up there. In other words, 95L would most certainly be up there if it weren't for technical problems.

The SSD satellite links aren't updating very well, either, and it appears that most of the images of 95L haven't been updated since early this morning.

The most recently updated image I could find just now is actually the Meteosat from 1800Z, which shows a very well-developed subtropical storm out there, IMHO. 95 has deep convective banding arcs wrapping around 60% or so of the coc. In all actuality, if the trends of today continue, which are actually verifying some of the more aggressive model runs, even a TS Pablo looks like a distinct possibility before the end of the year.

Several have begun referring to 2007 as "2005 Lite," which seems so very appropriate in many ways. This is not discounting the devastating effects from systems such as Olga, Noel, Felix, Erin & Dean, but I merely agree with some other posts above which have referred to this season as having been very active, and yet relatively quiet (at least along the coastal U.S.). For a really interesting read, check out the history of TS Erin post-landfall.

Morning Visible Aqua - MODIS 1535Z 12/29/07


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Ed DunhamAdministrator
Meteorologist & CFHC Forum Moderator


Reged: Sun
Posts: 2565
Loc: Melbourne, FL
Re: 2550SM East of Central Florida [Re: cieldumort]
      #79658 - Sun Dec 30 2007 12:12 AM

NHC did issue a Special Tropical Disturbance Statement Saturday afternoon, but since it was not posted on the NHC site I'll post it in full here:

WONT41 KNHC 291919
DSAAT
SPECIAL TROPICAL DISTURBANCE STATEMENT
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
315 PM AST SAT DEC 29 2007

A SURFACE LOW PRESSURE SYSTEM CENTERED OVER THE EASTERN ATLANTIC
OCEAN ABOUT 950 MILES SOUTHWEST OF THE AZORES HAS BEEN GRADUALLY
ACQUIRING SOME SUBTROPICAL CHARACTERISTICS DURING THE PAST DAY OR
SO. THIS SYSTEM HAS BEEN PRODUCING GALE-FORCE WINDS...MAINLY TO
THE NORTH AND EAST OF ITS CIRCULATION CENTER...AND IT COULD BECOME
A SUBTROPICAL STORM LATER TODAY OR TOMORROW AS IT REMAINS NEARLY
STATIONARY.

FURTHER TROPICAL DISTURBANCE STATEMENTS WILL BE ISSUED AS NECESSARY.
ADDITIONAL INFORMATION ON THIS SYSTEM CAN BE FOUND IN HIGH SEAS
FORECASTS ISSUED BY THE NATIONAL WEATHER SERVICE...UNDER AWIPS
HEADER NFDHSFAT1 AND WMO HEADER FZNT01 KWBC.

$$
FORECASTER KNABB/SISKO

The system now has sustained winds of 35 knots and central pressure is down to 1006MB. It probably has about 36 more hours before increasing shear will begin to weaken the system.
ED


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cieldumort
Moderator


Reged: Mon
Posts: 1403
Loc: Austin, Tx 30.40N 97.80W
Re: 2550SM East of Central Florida [Re: Ed Dunham]
      #79659 - Sun Dec 30 2007 04:11 AM

95L has gotten battered and squeezed a bit tonight by the encroaching shear from the west. Deep convective banding that had been making some respectable inroads to fully encircling the LLC while developing an upper-level anticyclone in a fashion at times more tropical-like than subtropical, has been getting shunted northeast and east in the process, leaving once again a rather well-defined mid to upper level center rather barren of any deep convection.

For what it's worth, 95L quite possibly spent about 12-18 hours as a subtropical storm Saturday, just not "standard-enough" for what NHC likes to see before they enter it into the history books with a name. I think that the TWD that went up early Saturday night earns high marks for plain talk and candor, and speaks well to this point:

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
705 PM EST FRI DEC 29 2007

BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2315 UTC

...SPECIAL FEATURE...

THE WELL-DEFINED NON-BAROCLINIC CYCLONE CONTINUES IN THE
NORTHEAST ATLANTIC NEAR 28N38W. THE SYSTEM HAS BEEN DRIFTING
NORTH-NORTHEASTWARD DURING THE DAY AND HAS DEVELOPED PRONOUNCED
ANTICYCLONIC OUTFLOW IN THE UPPER TROP. DESPITE WATER
TEMPERATURES NEAR THE CYCLONE OF AROUND 22-23C...MODERATE
CONVECTION HAS BEEN PERSISTENT ON THE NORTHEAST SEMICIRCLE.
SATELLITE CLASSIFICATIONS SUGGEST THAT THE SYSTEM COULD BE A
MINIMAL SUBTROPICAL STORM. QUIKSCAT WINDS...WHILE HAVING THE
USUAL AMBIGUITY ISSUES IN RAINY CONDITIONS...INDICATE THAT GALE
FORCE WINDS LIKELY ARE OCCURRING IN THE NORTHERN SEMICIRCLE.
TROPOSPHERIC VERTICAL SHEAR IS ABOUT 20 KT AS THE STRONGEST
UPPER TROP WESTERLIES ARE BYPASSING THE CYCLONE TO THE NORTH AND
THE SOUTH. THE CYCLONE SHOULD MEANDER OVER THE NEXT 36 HOURS
BEFORE BEING PUSHED OFF TOWARD THE WEST OR SOUTHWEST BY A
DEVELOPING MID-OCEAN RIDGE ON MONDAY. GIVEN THAT THE VERTICAL
SHEAR SHOULD INCREASE SUBSTANTIALLY TOMORROW...TONIGHT MAY BE
THE LAST OPPORTUNITY FOR THIS SYSTEM TO GAIN A BIT MORE
ORGANIZATION TO ITS CONVECTION AND MAKE THE TRANSITION TO A
NAMED SUBTROPICAL STORM.

The most recent batch of model runs were a little interesting. At 18Z both GFDL and HWRF suggested a meandering cyclone generally heading WSW or SW, and peaking out at about 55-60 knots at the surface, with pressure down to as low as the mid-upper 990s. I'm guessing that if the 00Z runs have had time to ingest the interaction with the increased shear this may now be in play some.


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allan
Weather Master


Reged: Thu
Posts: 468
Loc: Palm Coast, Florida 29.55N 81.20W
Re: 2550SM East of Central Florida [Re: cieldumort]
      #79660 - Sun Dec 30 2007 08:17 AM

According to some wunderground bloggers, and I mean the smart ones lol, Pablo (which even though it's not named, it SHOULD HAVE BEEN) is undergoing extratropical transition?? What is up with this? This was surely a Subtropical Storm all day, why not name the system? NHC gets me aggrevated sometimes when they wait for the last minute. Now the system doesnt look worthy enough to be named anymore. Post analyiss needs to name this storm.

--------------------
Allan Reed - 18,9,5


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Ed DunhamAdministrator
Meteorologist & CFHC Forum Moderator


Reged: Sun
Posts: 2565
Loc: Melbourne, FL
Re: 2550SM East of Central Florida [Re: allan]
      #79661 - Sun Dec 30 2007 10:49 AM

From the NHC Description for a Subtropical cyclone: "A non-frontal low pressure system that has characteristics of both tropical and extratropical cyclones."

The key is a "non-frontal low pressure system". Even yesterday the system maintained a decayed frontal trough that extended well to the southwest of the low. If the system could have separated itself from the old frontal trough it would have satisfied the definition, but I don't think that it quite made it. Another factor was the lack of any true tropical banding that would have enhanced convection - even if that convection was well removed from the center. The general eastward motion was not anticipated - at least not to the extent that did occur - and that probably placed the system in position to force interaction with the frontal boundary to the east and prevented full hybrid transition in the lower levels of the system. As NHC noted in their new Special Tropical Disturbance Statement at 11am AST, there is still a chance for reclassification in the next 24 hours, but this is not a high probability if the system continues to maintain an eastward component in its movement. It would probably take some new data, i.e., a delayed buoy or ship report before post analysis would be considered - but even that could still happen.
ED


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HanKFranK
User


Reged: Mon
Posts: 1841
Loc: Graniteville, SC 33.56N 81.82W
Re: 2550SM East of Central Florida [Re: Ed Dunham]
      #79662 - Sun Dec 30 2007 12:17 PM

mighty close. i don't know if the decayed trough was enough to exclude it. if post-analysis puts it up as subtropical storm 16, the life span will be extremely short. it's elongation today and extratropical appearance will probably be followed by another occlusion and the southwestward drive, but the little donut hole of favorable u/a conditions is pretty much gone now... all the thing really had was a 12-18 hr run where it may have satisfied the criteria. if i had to bet on the NHC's future actions, i'd guess it will remain an extratropical system in post-analysis.
nice little footnote to end 2007 on.
HF 1716z30december


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allan
Weather Master


Reged: Thu
Posts: 468
Loc: Palm Coast, Florida 29.55N 81.20W
Re: 2550SM East of Central Florida [Re: Ed Dunham]
      #79663 - Mon Dec 31 2007 10:36 AM

Here we go again with 95L, shear is favorable and it's starting to look a bit better. However, I still dissagree with most and believed this should have been named Saturday, it looks like it wont transition to extratropical as I thought yesterday, it basically cut off again and shear has lowered to 5-10 knots. We might not get Pablo, it could be Arthur.. which would be a record and an amazing event!

--------------------
Allan Reed - 18,9,5


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cieldumort
Moderator


Reged: Mon
Posts: 1403
Loc: Austin, Tx 30.40N 97.80W
Re: 2550SM East of Central Florida [Re: HanKFranK]
      #79664 - Mon Dec 31 2007 10:56 AM

Yeah, I'm in the could-have/should-have camp, myself. The remaining hint of a decaying post-frontal trof left connected to 95L is splitting hairs, and I think essentially arguing over unnecessary minutia. The vast majority of the features of this cyclone have been consistent with a short-lived subtropical storm even briefly attempting to become tropical before starting a bit of extra-tropical transition, and now has been left meandering as a 45 knot 1004mb "remnant low" (as of this morning) while in the process of spinning down, most probably.

For a feature that went without a name, 95L, whatever NHC ultimately chooses to do with it post-season, has had far more "Special Feature" write-ups in the TWDs than any non-named system I can think of in recent memory. Additionally, the few STDSs which were issued have covered several days now.

Given the above, and also that a couple of the scat passes suggested winds could have easily been in the 40-50 knot range for a few cycles worth of time, plus a solid run of satellite-based interpretations of subtropical storm intensity, and considering everything in this most recent TWD I quote below, I think there is plenty of ammunition for those who believe it should be added in post-season to argue the case.

...SPECIAL FEATURE...
A LARGE LOW PRES SYSTEM IS LOCATED ABOUT 850 NM SW OF THE AZORES
NEAR 26N36W. A FORTUITOUS REPORT FROM DRIFTING BUOY 62901 AT 00Z
REPORTED A PRES OF 1004.6 MB VERY NEAR THE LOW-LEVEL
CENTER...ACCORDINGLY THE MIN PRES WAS DROPPED TO 1004 MB.
HOWEVER...THE OVERALL CLOUD PATTERN HAS DETERIORATED SINCE THAT
TIME SO IT IS POSSIBLE THAT THE PRES MAY HAVE INCREASED
SLIGHTLY. EARLIER THIS MORNING...CONVECTION WAS MOST ORGANIZED
IN THE NW QUADRANT AND WAS GENERALLY MODERATE IN NATURE...CLOUD
TOPS NEAR -60 C...ACROSS THE QUADRANT. THIS CONVECTION HAS NOW
ROTATED TO THE SW QUADRANT AND HAS GENERALLY DECREASED IN AERIAL
COVERAGE AS MODERATE CONVECTION IS CONFINED FROM 25N-27N BETWEEN
37W-39W. AN ASCAT PASS AROUND 00Z REVEALED A FEW 45 KT WIND
VECTORS NEAR THE SWATH EDGE IN THE NW SEMICIRCLE...WHERE THE
PRESSURE GRADIENT IS TIGHTEST DUE TO HIGH PRES CENTERED TO THE
NW. AT ABOUT THE SAME TIME...A VERY CONVENIENT JASON ALTIMETER
PASS CROSSED THE CIRCULATION REPORTING MAX SEAS NEAR 26 FT AND A
300 NM 12 FT SEA RADII N OF THE CENTER. MORE RECENTLY...A QSCAT
PASS AROUND 0830Z SHOWED A FEW BELIEVABLE 40 KT WIND VECTORS W
OF THE CENTER.


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