BillD
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From the TWD issued at 8:05 PM
A NON-TROPICAL AREA OF LOW PRESSURE LOCATED ABOUT 320 NM
WEST-SOUTHWEST OF BERMUDA NEAR 30N70W...ANALYZED 1008 MB...HAS
GENERALLY CHANGED LITTLE IN STRUCTURE. ... HURRICANE
HUNTER AIRCRAFT INDICATE THAT THE LOW HAS NOT YET ACQUIRED THE
CHARACTERISTICS OF A SUBTROPICAL OR TROPICAL CYCLONE.
FWIW, several of the models are developing something out of this, but no mention of that in the discussion.
Bill
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typhoon_tip
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Quote:
From the TWD issued at 8:05 PM
A NON-TROPICAL AREA OF LOW PRESSURE LOCATED ABOUT 320 NM
WEST-SOUTHWEST OF BERMUDA NEAR 30N70W...ANALYZED 1008 MB...HAS
GENERALLY CHANGED LITTLE IN STRUCTURE. ... HURRICANE
HUNTER AIRCRAFT INDICATE THAT THE LOW HAS NOT YET ACQUIRED THE
CHARACTERISTICS OF A SUBTROPICAL OR TROPICAL CYCLONE.
FWIW, several of the models are developing something out of this, but no mention of that in the discussion.
Bill
They won't do that, pretty much ever. There is no purely tropical model beyond statistical based guidance..which does purely tropical physics. Everything is either baroclinic [meaning, based on horizontal differentiable medium] or limited-scaled baroclinic at best, and that means that inherently, they are prone to inaccuracies, particularly during the genesis phase.
No one want's to "officiate" a statement based on inherently erroneous tools. So it is understandable policy that they mention model coverage only after a system is already trackable. The reason why is because storm genesis outside the tropics is physcically different, in that it is based on fluid mechanics combined with temperature and dp gradients across that fluid medium. In the tropics, however, the quadrants are even -- typically -- and the only engine is the thermodynamics in the vertical, such that a coupled oceanic heat content with the lower atmosphere provides an abundance of convective available potential energy to rising parsels.
When you have a cyclonic curvature at upper levels of that which is observable this night impacting the area, this creates a medium conducive to extra-tropical cyclogensis. I have not been stellar in my own anticipations of this system evolution thus far.. I did not foresee this trough establishing its self with this strength. The overal picture has changed toward one which will take a long time if ever, to become tropical entity.
Edited by typhoon_tip (Thu Sep 06 2007 01:06 AM)
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typhoon_tip
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99L looks very ragged tonight. I'm not sure it's going to survive. Does anyone have any specifics on when the shear is supposed to lessen?
Good question! This is instrumental in this system's future. The shear was not very well modeled.
There has been strong diurnal convection in the lower Mississippi Valley the last 2 days and this is fluxing convective heat release into the atmosphere in the area and into the SE U.S. That raises heights because of the heat insert causing an expansion of the medium -- like filling a balloon. But there is no rubber boundary in the atmosphere so the expansion causes the wind to increase as it flows outward from areas of expansion to areas of less pressure. The result is an increase in the ridge intensity over the SE, which causes increases wind flow into the weakness off the SE Coast. The trough appears stronger than modeled, because the models ultimately have not been handling the consequence of latenet heat release of convection in the deep south over the Mississsippi Valley very well.
I believe this is the cause for the trough digging into 75W and ultimately the shear stress on the system.
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nc_tropical_wx79
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I'm sorry I didn't understand none of that! So will the shear lessen soon or around what time and is it safe to write off 99L as a tropical entity now?
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W.D. Duncan
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BLTizzle
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I believe he is referring to radiational cooling. For instance, if you pour salt on a table and stand directly over it and blow on it, its going to spread out into a circle. Picture the air over the southeast as the salt, and the atmosphere as the table, when the heated air hits the atmosphere, it spreads out, thus adding shear to 99L. Since the heated air has nowhere to go once it escapes the lower levels, it has go be distributed evenly.
Hope that helped
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Brandon in Eufaula, AL - experienced TS Alberto ('93) Opal ('95), Georges ('98), Ivan ('04), Katrina ('05) (I was in Tuscaloosa AL roughly 70 miles SSE of Columbus, MS)
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HanKFranK
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that upper low, which was poorly foreseen and highly underestimated in just about all the modeling, laid 99L flat. the system is finally 'blocked', i.e. track is bending south and should turn west shortly. at the same time that upper low hasn't cut off, or moved west of the system, or done any of the things that would have lessened shear. 99L behaved more like a frontal low, clinging to the western side of the upper low, and has now lost much of its definition and convective activity as the induced baroclinic conditions subsided.
all of the models are out to lunch. if anything survives this (which has longer odds now, with all the subsidence to fight and so little definition) the near unanimous contention that it will latch onto the first shortwave and recurve near north carolina is probably also out to lunch. for whatever remains, i'd expect it to sort of jerk and bob around in weak steering, working slowly westward under the ridge while it lasts. otherwise, the near tropcial cyclone we had the other day is a wash.
eastern atlantic has nothing to offer. massive, well-defined waves with no convection are cans of corn. the upper low cutting off southeast of newfoundland has a better chance than the big wave near 45w. modeling develops another storm later, but all recurve it well off out to sea.
the ominous look of things a couple days ago is evaporating. if 99L smears out completely and never gets out from under the shear, we're into another lull.
season so far has been defined by long periods of nothing between weak storms, and huge category fives barreling west across the caribbean.
HF 1137z06september
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invest1
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I agree. Even yesterday it did not look all that impressive due to a lack of moisture around the center. My question is, it appeared to have moved a little s over night and looks to be trying to wrap some moisture around, albeit very little, could this thing servive and if it did with all the dry air around how much of an impact would the gulf stream have on it if any?
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hurrev
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Looking at the vis sat loop, 99L seems to be as good as it did yesterday and seems to be pulling away from the front. I also noticed that the 06Z seems to be more impressed with the development than the 00Z model output seemed. At 00Z had it going in around Wilm NC with 60 mph and 06Z now has it in Wilm with 95 mph. Am I reading this model correctly because by no means am I a met!
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Ed in Va
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You are correct in your reading of the model, but I believe the wind speed is measured above the surface and is therefore stronger than the actual on land. In interpreting models, look for consistency over time, not just a comparison of two consecutive ones.
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Survived Carol and Edna '54 in Maine. Guess this kind of dates me!
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typhoon_tip
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I agree with the 8:00am update:
http://flhurricane.com/cyclone/showflat....SSID=#Post77996
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allan
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99L looks like it is now cutting off from the frontal mess.. all of that will head out to see as the little swirl (99L), is now moving or even slowly drifting south into favorable shear, I expect this system to get much better organized in structure and convection by tommorrow morning.. the forecast track (so far, anything can change beyond that) is much like Gustav in 2002. After 94L (Felix) I am not writing this storm off yet.. looks to be pulling away from the trough that is tearing it apart.. and some tiny indications of storms around this swirl.
http://hadar.cira.colostate.edu/ramsdis/online/trop_ge_storm_relative_1.html
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Allan Reed - 18,9,5
Edited by allan (Thu Sep 06 2007 01:09 PM)
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hurrev
Unregistered
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Just noticed that the is still showing 06Z. have they stopped running models on 99L?
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Lee-Delray
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They stopped covering 99l earlier today. At this time there doesn't seem anything to cover.
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nc_tropical_wx79
Weather Guru
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If you look at 99L now it looks like convection is trying to start building over the LLC so it may still have a chance yet.
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W.D. Duncan
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Bastardicasting
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(Wishcasting is not permitted on this site - post deleted.)
Edited by Ed Dunham (Fri Sep 07 2007 08:19 AM)
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scottsvb
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lol now that is JB talking...haha soo funny. Actually 99l is straight on forecast (besides strength) Im beginning to wonder though how far south that trough will dig and if the ridge over the deep south will slide to off the mid-atlantic and SE early next week.
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typhoon_tip
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Quote:
that upper low, which was poorly foreseen and highly underestimated in just about all the modeling, laid 99L flat. the system is finally 'blocked', i.e. track is bending south and should turn west shortly. at the same time that upper low hasn't cut off, or moved west of the system, or done any of the things that would have lessened shear. 99L behaved more like a frontal low, clinging to the western side of the upper low, and has now lost much of its definition and convective activity as the induced baroclinic conditions subsided.
all of the models are out to lunch. if anything survives this (which has longer odds now, with all the subsidence to fight and so little definition) the near unanimous contention that it will latch onto the first shortwave and recurve near north carolina is probably also out to lunch. for whatever remains, i'd expect it to sort of jerk and bob around in weak steering, working slowly westward under the ridge while it lasts. otherwise, the near tropcial cyclone we had the other day is a wash.
eastern atlantic has nothing to offer. massive, well-defined waves with no convection are cans of corn. the upper low cutting off southeast of newfoundland has a better chance than the big wave near 45w. modeling develops another storm later, but all recurve it well off out to sea.
the ominous look of things a couple days ago is evaporating. if 99L smears out completely and never gets out from under the shear, we're into another lull.
season so far has been defined by long periods of nothing between weak storms, and huge category fives barreling west across the caribbean.
HF 1137z06september
Hank',
this may not be the time nor place but I get a somewhat different vibe than you concerning the TW that has just come off near Sierra Leone. Significant cyclonic turning with an approximate lat/lon axis near 22W/9N and ongoing moderate to strong convection contained.
John
(Just a reminder to all that comments on the latest wave off of Africa are better suited to another Forum since this wave was not mentioned in the Main Page leadoff article.)
Edited by Ed Dunham (Fri Sep 07 2007 08:25 AM)
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Ed in Va
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Agreed, but maybe only looks better now because it looked some horrible earlier...still has a long ways to go.
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Survived Carol and Edna '54 in Maine. Guess this kind of dates me!
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John Mellonhead
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Far from a pro here, but enjoy the site. Haven't checked in since getting whacked around in S. Florida a few years ago.
Anyway, is it just me or is the looking bang on? Looks like a clear circulation with some action cropping up now, and reverse throttle seems to have been thrown down. Does "Gabby" have basically a clean runway right into South Carolina at this point?
Thanks again for an informative website.
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Marcus
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Far from a pro here
Same here, I just like looking at the satellite pictures I 'spose  .
From what I've seen, 99 just keeps trying and trying; for myself, who knows little about weather patterns in general, it's been a perfect example of how wind shear can affect the formation of a storm, and how dry air can affect progression, so it's been very informative from that respect. For the last couple of days I haven't been able to see much reduction in the circulation, so if this shear does drop it might still have something of a chance. Unfortunately, my ability to read weather to know whether that's likely is pretty non-existent... what should I be looking for and from what information source will I be able to determine if/when that shear will end?
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