Srain Posted July 31, 2011 Author Share Posted July 31, 2011 lol...a re-position in the works... 31/1745 UTC 13.1N 56.8W T1.5/1.5 91L Link to comment Share on other sites More sharing options...
jpeters3 Posted July 31, 2011 Share Posted July 31, 2011 31/1745 UTC 13.1N 56.8W T1.5/1.5 91L If this is true that this is where the strongest low is forming, throw all the model runs in the trash because that means all the models latched on to the wrong area (correct me if I'm mistaken), I believe the nested models have the center "imposed" based on the observed center of the system - this is called "vortex bogusing" Link to comment Share on other sites More sharing options...
OSUmetstud Posted July 31, 2011 Share Posted July 31, 2011 lol...a re-position in the works... 31/1745 UTC 13.1N 56.8W T1.5/1.5 91L strange...the cimss analysis has the greatest 850 and 700mb vort around 53/54W. It is also stronger in magnitude than this time yesterday. Link to comment Share on other sites More sharing options...
CoastalWx Posted July 31, 2011 Share Posted July 31, 2011 MCSs often occur in sheered environments, where the orientation of the storm relative flow (not sheer) is a signifcant impacting factor on the behavior of the system. It doesn't chance the fact that "absolute sheer" is the same as "storm relative sheer". Unlike MCSs, TCs thrive in low-sheer environments, where there is essentially no storm relative flow Good point and thanks for that clarification on shear. I was thinking a similar thought as Wes had. I wasn't really seeing the big picture in terms of absolute or bulk shear. Link to comment Share on other sites More sharing options...
dan88 Posted July 31, 2011 Share Posted July 31, 2011 One can see the surface circulation around that position on the visible as a broad, largely exposed low level swirl , and that low is currently falling behind the front thunderstorm complex because of it's current limited movement, and with time will likely merge with the mid/upper level low centers in the Eastern complex, at which point we will likely see Emily. It is also possible that this fades, and a new circulation develops with the eastern complex, seeing that this is now falling behind the initial complex of storms. Link to comment Share on other sites More sharing options...
usedtobe Posted July 31, 2011 Share Posted July 31, 2011 31/1745 UTC 13.1N 56.8W T1.5/1.5 91L If this is true that this is where the strongest low is forming, throw all the model runs in the trash because that means all the models latched on to the wrong area That's a Dvorak classification, correct? Is it one from SAB or TPC? Looking at the imagery, I still see two possible circulations, one on the southeast flank of the western blob and another in the eastern batch of convection. That makes it had to know where the actually circulation is and which one will be the real one if what I think I'm seeing is what is there. Link to comment Share on other sites More sharing options...
Amped Posted July 31, 2011 Share Posted July 31, 2011 lol...a re-position in the works... 31/1745 UTC 13.1N 56.8W T1.5/1.5 91L All I see is a 1010mb pressure and winds out of the NNE gusting to 20mph at Bridgetown Barbados. The mid level center appers to be southeast of there. Link to comment Share on other sites More sharing options...
EasternUSWX Posted July 31, 2011 Share Posted July 31, 2011 Wonder what ever happened to recon. No idea what is going on out there with it. Link to comment Share on other sites More sharing options...
ohleary Posted July 31, 2011 Share Posted July 31, 2011 From what I see, while the western thunderstorm complex is surely moving west, there is a low level circulation that has been associated with the western complex centered at roughly 12N 57W which is falling behind the westerly moving complex, and is currently moving little. Right the wave is moving quickly leaving the low level circulation behind... Link to comment Share on other sites More sharing options...
usedtobe Posted July 31, 2011 Share Posted July 31, 2011 Right the wave is moving quickly leaving the low level circulation behind... That's what I see too. Link to comment Share on other sites More sharing options...
Srain Posted July 31, 2011 Author Share Posted July 31, 2011 All I see is a 1010mb pressure and winds out of the NNE gusting to 20mph at Bridgetown Barbados. The mid level center appers to be southeast of there. I guess that answers that... AL, 91, 2011073118, , BEST, 0, 135N, 528W, 30, 1007, LO Link to comment Share on other sites More sharing options...
wxmeddler Posted July 31, 2011 Share Posted July 31, 2011 lol...a re-position in the works... 31/1745 UTC 13.1N 56.8W T1.5/1.5 91L .. I'm confused. I'm hoping the G-IV will clear things up a little. Link to comment Share on other sites More sharing options...
ohleary Posted July 31, 2011 Share Posted July 31, 2011 Speaking of aircraft, where is the G-IV departing from and how much data, if any, will get ingested into the 0Z models? We are getting it in time for the 18Z cycle. The 18Z NAM reports 5 dropwinsonde and 6 flight level recon reports dumped...though I can't say if they'll pass QC and be assimilated. Here you can see the dump reports for each cycle...the 18Z NAM hasn't updated yet though. http://www.nco.ncep....wprod/realtime/ Link to comment Share on other sites More sharing options...
janetjanet998 Posted July 31, 2011 Share Posted July 31, 2011 Right the wave is moving quickly leaving the low level circulation behind... That may become the new LLC for both blobs? Time will tell look at the visible and you can see the low clouds tryin to move around this area....very large circulation if this is indeed the case. Link to comment Share on other sites More sharing options...
wxmeddler Posted July 31, 2011 Share Posted July 31, 2011 We are getting it in time for the 18Z cycle. The 18Z NAM reports 5 dropwinsonde and 6 flight level recon reports dumped...though I can't say if they'll pass QC and be assimilated. Here you can see the dump reports for each cycle...the 18Z NAM hasn't updated yet though. http://www.nco.ncep....wprod/realtime/ Thanks for the link! Link to comment Share on other sites More sharing options...
janetjanet998 Posted July 31, 2011 Share Posted July 31, 2011 bouy 41040 winds just went south after being east all day...this is just on the north side of the eastern blob bouy at 14.5N 53.0W Link to comment Share on other sites More sharing options...
Typhoon Tip Posted July 31, 2011 Share Posted July 31, 2011 mathematically they are the same, since sheer is a vector difference. Imagine a case where you have this idealized zonal wind profile (no v component): 3000 m 40kts 2000 m 30kts 1000 m 20kts sfc 10kts take the vector difference over 3000 m, you get 40 kts bulk sheer. so "relative sheer" = "absolute sheer", period. If we approximate the mean wind vector through this layer by simply averaging these velocities, we arrive at 25kts. So the storm relative wind field would be this: 3000 m 25 kts 2000 m 5 kts 1000 m -5 kts sfc - 15 kts take the vector difference over 3000 m, you still get 40 kts bulk sheer. See the point? generalized: C = storm motion, V1= absolute wind at low level V2= absolute wind at higher level Bulk "absolute" sheer over layer between V2 and V1 = V2-V1 V1 - C = storm relative wind at low level V2 - C = storm relative wind at higher level Storm relative sheer = (V2 - C) - (V1 - C) = V2-V1 This is precisely the point I just made regarding negative differential of storm motion against the ambient vector. Agreed! Link to comment Share on other sites More sharing options...
icebreaker5221 Posted July 31, 2011 Share Posted July 31, 2011 That makes sense! Thanks for correcting me. It also shows why I shouldn't stick my head in tropical threads too much unless they relate to rainfall or severe weather at landfall. t post much on the Maybe I'm a little bit late to the party, but wanted to throw in a few remarks: Numerical simulations, as well as some observational evidence, has shown that westerly shear should be more detrimental than easterly shear (in the NH) due to the beta-effect. A northwesterly beta-shear should be additive to a westerly environmental shear and counteractive to an easterly environmental shear. However, the magnitude of the beta-shear is dependant upon the difference in strength with height of the vortex itself due to the differential advection of beta with height by the cyclone. So this would be much more relevant for mature TCs, and not tropical waves. Of course the direction of the shear relative to the dry air is also relevant, as has been discussed a lot recently. I would like to add that a mid-level jet maximized at the level of driest air will also be more detrimental to the TC than a jet of equal magnitude at the level of a moist tongue, with dry air at a non-advecting level. In either case the magnitude AND direction of the shear could be the same, the TPW of the air upshear could be the same, but with dramatically different results. Finally, some recent idealized simulations (Nolan, some others) without dry air OR shear have STILL shown a difference in the sensitivity of the TC to shear direction, and even whether the wind profile is veering or backing with height, even given equal magnitudes of shear. I believe there are some hypotheses to explain this phenomenon, but not yet a consensus. Link to comment Share on other sites More sharing options...
phil882 Posted July 31, 2011 Share Posted July 31, 2011 That is correct. This would also increase the storm motion as well, since storm motion is determined by the mean-layer wind...hence why there's no such thing as "storm-relative" shear. We've had this discussion for a few years in these threads. I've discussed the matter with someone from the NHC and they didn't seem to believe in the concept of storm relative shear, either. I'm wondering why or how storm relative shear would be any different than absolute shear. I think the reason why people get confused and believe there is a such thing as "storm-relative shear" is based on what level of the atmosphere is causing the phenomena. For example, there are certain situations where the low level flow is too fast and it outruns the slower upper level flow. This is still absolute shear, but it makes it seem like the low level flow is causing the bulk of the shear, hence the term pegged "storm-relative" since the low level motion that moves the low level vortex seems to be causing the bulk of the absolute shear. The flow vector might be in the same direction, but if the low levels are easterly at 25 knots, while the upper levels are easterly at a mere 5 knots, the shear will still impact the system and the convection will be "blown" off to the east. This looks different than a typical shearing pattern where the low level flow and the upper level flow are moving in different directions. Here the low level flow might be easterly at 10 knots, but the upper level flow is westerly at 10 knots. It creates the same magnitude of absolute shear, but looks a lot different on satellite imagery because the low level flow is much slower and you can visually see the upper level flow moving in the opposite direction on earth-relative satellite imagery. Perhaps a better way to peg different types of shear regimes would be to call the first case outlined above "speed shear" since both wind vectors in the low and upper levels are in the same direction, just a different magnitude. The second case is an excellent example of "directional shear" where the low and upper level flow are moving in different directions, even if they are the same magnitude. It is all still absolute shear, but that doesn't mean each shearing environment, despite having the same magnitude, is the same. The relationship between shear and dry air in some respects is more important than the magnitude (as we just witnessed in Tropical Storm Don's case). Link to comment Share on other sites More sharing options...
icebreaker5221 Posted July 31, 2011 Share Posted July 31, 2011 (correct me if I'm mistaken), I believe the nested models have the center "imposed" based on the observed center of the system - this is called "vortex bogusing" I believe that he was implying that in previous (HWRF/GFDL) runs, the vortex was imposed in the wrong location. If the 56.6 W center fix were to be correct, then it would look like we were estimating the center via satellite in a different location than indicated by reconnaissance, so earlier runs would be initialized with the wrong center of circulation. That said, the vortex message posted at that time appears to have been thrown, since the latest official LON is still at 52.8 W, not 56.8 W. Link to comment Share on other sites More sharing options...
janetjanet998 Posted July 31, 2011 Share Posted July 31, 2011 bouy data as of 20z Link to comment Share on other sites More sharing options...
Ed Lizard Posted July 31, 2011 Share Posted July 31, 2011 bouy data as of 20z Still the lack of flow from the North around the Eastern complex, meaning an elongated elliptical center. Oh, and outflows suggesting dry air may be hindering the Eastern center. Link to comment Share on other sites More sharing options...
phil882 Posted July 31, 2011 Share Posted July 31, 2011 Just based on a quick visible loop, it seems that the broad low level center is still quite elongated and wedged in between two greater areas of convection. This likely does not have the organization needed yet to be considered a tropical cyclone. Link to comment Share on other sites More sharing options...
janetjanet998 Posted July 31, 2011 Share Posted July 31, 2011 Just based on a quick visible loop, it seems that the broad low level center is still quite elongated and wedged in between two greater areas of convection. This likely does not have the organization needed yet to be considered a tropical cyclone. I think so too, but I would put the center just NNW of your low..but it seems to me the two blobs are combining around that center Link to comment Share on other sites More sharing options...
bluewave Posted July 31, 2011 Share Posted July 31, 2011 this is absolutely correct - the orientation of the shear matters, and there are no magical thresholds that dictate development or weakening. RE: shear, not sheer - I believe I have written papers and misspelled this. Somebody needs to give me a good knock on the back of the head Wilma was an interesting case. http://www.nhc.noaa.gov/archive/2005/dis/al242005.discus.040.shtml? Link to comment Share on other sites More sharing options...
phil882 Posted July 31, 2011 Share Posted July 31, 2011 I think so too, but I would put the center just NNW of your low..but it seems to me the two blobs are combining around that center Yea... the center appears to be pretty broad though so its not really worth focusing on one particular area. It is a shame though that the recon obs went dead. Overall though, its going to take a bit better convective organization before this system becomes a tropical cyclone. Link to comment Share on other sites More sharing options...
Typhoon Tip Posted July 31, 2011 Share Posted July 31, 2011 The longer these disparate vorticity maxims interfere with the others ability to become dominant the farther west this entire region will move along with the environmental flow. When/if a TC becomes better organized its vertical structure will then as a whole be more prone to moving along with the steering level wind field, which is probably why many of the models move this through the northern Leewards. There is already a slight north bias of the models recent runs and it may be because they are keying in on the vortex closer to 52w/14n, and by supposition are missing the limiting interaction with the vortex near 58w/13n. Already we begin to question the robustness of the GFDL and HWRF 12z runs, at least in the early time intervals. It seems they are always on a fast bias with the spin up momentum. My personal belief is that the system near 52/14 will become the dominant of the two, and probably absorb the westerly center based purely on PGF becoming overwhelming and shredding/shearing the low-level vorticity associated with 58/13 (timing all that is next to impossible). The latter cyclone aspect has a clearer and larger mass associated already with its circulation. Caveat, this based purely on satellite observation. Recon report should be interesting/revealing. Satellite can lie. We have seen plenty of systems with clear and present cyclonic motion in cloud field, but then recon fails to close off circulation, before... It is possible that the west center has a better low level circulation, where the east system has a better elevated/mid level vortex with comparably less low level involvement. In other wods ... a big mess. If that is the case I no longer have a personal belief! Link to comment Share on other sites More sharing options...
thegreatdr Posted July 31, 2011 Share Posted July 31, 2011 I know I'm late to the storm-relative shear/vertical wind shear party. I was confused myself a few years back, so I contacted someone at NHC that believes in expressing the mathematical representation (vertical wind shear) and someone at SPC who believes storm-relative shear is a more visual/conceptual way of looking at the idea. The two debated for a while, but there was no real consensus. The point is, the two are talking about the same concept, and one concept is used more within severe weather circles and one is used more within TC circles. You see this a lot within meteorology...the math-based versus conceptual model-based camps of thinking. Different people will pick different terms when discussing the same issue, normally based upon their process of learning. We've had this discussion for a few years in these threads. I've dgoes.noaa.gov/HURRLOOPS/hpvs.html discussed the matter with someone from the NHC and they didn't seem to believe in the concept of storm relative shear, either. I'm wondering why or how storm relative shear would be any different than absolute shear. Link to comment Share on other sites More sharing options...
janetjanet998 Posted July 31, 2011 Share Posted July 31, 2011 ABNT20 KNHC 312053 TWOAT SPECIAL TROPICAL WEATHER OUTLOOK NWS NATIONAL HURRICANE CENTER MIAMI FL 455 PM EDT SUN JUL 31 2011 FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO... SPECIAL OUTLOOK ISSUED TO UPDATE DISCUSSION OF THE ELONGATED AREA OF LOW PRESSURE APPROACHING THE LESSER ANTILLES. UPDATED...COMMUNICATIONS PROBLEMS HAVE LIMITED THE AMOUNT OF DATA RECEIVED FROM THE AIR FORCE RESERVE AIRCRAFT INVESTIGATING THE ELONGATED AREA OF LOW PRESSURE LOCATED ABOUT 500 MILES EAST OF THE NORTHERN WINDWARD ISLANDS. HOWEVER...REPORTS FROM THE AIRCRAFT ...ALONG WITH SATELLITE IMAGERY AND SURFACE OBSERVATIONS...INDICATE THAT THE SYSTEM DOES NOT YET HAVE A WELL-DEFINED SURFACE CIRCULATION. A SECOND AREA OF SHOWERS AND THUNDERSTORMS HAS FORMED TO THE WEST OF THE MAIN DISTURBANCE...AND WILL BRING LOCALLY HEAVY RAINFALL AND GUSTY WINDS TO PORTIONS OF THE LESSER ANTILLES TONIGHT. CONDITIONS ARE EXPECTED TO REMAIN FAVORABLE FOR A TROPICAL DEPRESSION OR TROPICAL STORM TO FORM...AND THIS SYSTEM HAS A HIGH CHANCE...NEAR 100 PERCENT...OF BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS AS IT MOVES WEST-NORTHWESTWARD NEAR 15 MPH. IF THE SYSTEM BECOMES A TROPICAL CYCLONE TONIGHT OR MONDAY ...TROPICAL STORM WATCHES OR WARNINGS WOULD BE ISSUED FOR PORTIONS OF THE NORTHERN WINDWARD ISLANDS AND THE LEEWARD ISLANDS ON VERY SHORT NOTICE...AND INTERESTS IN THESE AREAS SHOULD CLOSELY MONITOR THE PROGRESS OF THIS SYSTEM. ANOTHER HURRICANE HUNTER AIRCRAFT IS SCHEDULED TO INVESTIGATE THIS SYSTEM MONDAY MORNING. ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE NEXT 48 HOURS. Link to comment Share on other sites More sharing options...
wxmeddler Posted July 31, 2011 Share Posted July 31, 2011 It's going to be an interesting night tonight when the only GOES channel that is really critical to watching this wave develop is the the visible. Microwave from POES systems are going to be crucial tonight. Link to comment Share on other sites More sharing options...
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