NJHurricane Posted July 31, 2011 Share Posted July 31, 2011 if the original center can hold on wonder if the western blob can morhp into a decent outflow channel or if it will persist and inhibit steady intensification....the original mid level center seems like it wants to make another run at real consolidation but needs a decent burst of deep convection Link to comment Share on other sites More sharing options...
Ed Lizard Posted July 31, 2011 Share Posted July 31, 2011 My amateur understanding - accelerating flow, in the Eastern Caribbean, is associated with surface divergence, and decelerating flow is associated with surface convergence, one reason why the Western Caribbean is more favorable for development. A slowing system is in an area of increasing low level convergence. Faster low level flow also increases the shear, for equal upper flow, of course, assuming the usual upper Westerlies. Link to comment Share on other sites More sharing options...
Sunny and Warm Posted July 31, 2011 Share Posted July 31, 2011 There have been studies that have shown some negative correlation (faster storm motion is associated with less likelihood of intensification), but given that storm motion is pretty well-correlated with shear, I highly doubt that the storm motion itself does much. Would this be due to the storm moving more quickly into and out of differing regimes, and thus not able to be sustained in one environment for a long enough period of time to produce intensification? Also, has any study indicated the rate of forward speed required to negate the upwelling effect on storms, or is it somewhat dependent on strength of storm as well causing strong upwelling?? Sort of a chicken/egg question I guess. Link to comment Share on other sites More sharing options...
GaWx Posted July 31, 2011 Share Posted July 31, 2011 What did you consider an EC hit, Larry? North of Jax? 1) kush, I had originally worked with only ~St. Augustine north. However, I later decided to include the entire FL east coast to increase the size of the sample and also because I felt that including FL probably didn't really "taint" the sample. I found eight FL hurricane hits south of St. Aug. When looking at these eight alone (a bit risky due to fairly small sample size), the NAO correlation admittedly does appear to be between small and nonexistent with an avg. NAO of +0.1 and 5 of 8 having a +NAO. However, even here the lowest NAO was -0.746. So, even if the correlation for central/south FL is minor, it imo still supports the idea that a strongly NAO of ~-2 is going to make it very hard to get to FL. 2) Folks, I just did a quick GOM check. For 1950-2010, there were 14 storms east of the Lesser Antilles that later hit the U.S. Gulf coast as a hurricane (excluding the ones that hit FL earlier like Betsy, Katrina and Erin to avoid double counting) . The average NAO on the day of the hit was +0.3 (same as nongrazing east coast hits). Ten of the 14 (71%) had a +NAO and only four (29%) had a -NAO. Four were >+1.0, but only one was <-1.0 (Georges of 1998 with -1.494). Before I had checked this, I had thought the story might have been different from the east coast. These numbers suggest a similar situation for the Gulf with the possible exception of Georges. Even when considering Georges, the lowest NAO for the 40 U.S. hurricane hits was -1.494 and the average NAO was +0.3...i.e., a pretty decent partial positive correlation to the NAO. Link to comment Share on other sites More sharing options...
CUmet Posted July 31, 2011 Share Posted July 31, 2011 Faster low level flow also increases the shear, for equal upper flow, of course, assuming the usual upper Westerlies. 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. Link to comment Share on other sites More sharing options...
Ed Lizard Posted July 31, 2011 Share Posted July 31, 2011 TTCP 311700Z 29007KT 9999 SCT016 BKN300 30/22 Q1013 NOSIG JP-NE The lead cluster is going to take a while to fade away, IMHO. The surface circulation is still an elongated ellipse around two circulations, and while the Eastern cluster has better rotation on IR, the Western cluster has colder cloud tops and at least an equal looking surface presentation. Link to comment Share on other sites More sharing options...
LVblizzard Posted July 31, 2011 Share Posted July 31, 2011 looks like a David 1979 track according to the canadian It would probably recurve more sharply, though, instead of making landfall and going through the mid-atlantic. Link to comment Share on other sites More sharing options...
Sunny and Warm Posted July 31, 2011 Share Posted July 31, 2011 TTCP 311700Z 29007KT 9999 SCT016 BKN300 30/22 Q1013 NOSIG JP-NE The lead cluster is going to take a while to fade away, IMHO. The surface circulation is still an elongated ellipse around two circulations, and while the Eastern cluster has better rotation on IR, the Western cluster has colder cloud tops and at least an equal looking surface presentation. Which is more important at this stage of development, a mid level vortex that makes its way to the surface, or low level vortex making its way up? Link to comment Share on other sites More sharing options...
CUmet Posted July 31, 2011 Share Posted July 31, 2011 Would this be due to the storm moving more quickly into and out of differing regimes, and thus not able to be sustained in one environment for a long enough period of time to produce intensification? Also, has any study indicated the rate of forward speed required to negate the upwelling effect on storms, or is it somewhat dependent on strength of storm as well causing strong upwelling?? Sort of a chicken/egg question I guess. First question: I don't think that has anything to do with it. Second question: Upwelling is a function of both storm motion and storm strength, more so the latter. However, storms are more effective at drawing energy from the ocean at higher intensities as well. Link to comment Share on other sites More sharing options...
Amped Posted July 31, 2011 Share Posted July 31, 2011 12z CMC shifts west, looks like a close approach to FL at the end of the run. The storm passes directly over Hispaniola, though, which hinders strengthening. http://moe.met.fsu.e...&hour=Animation It also shows nicely the recurve Lattitude. The storm makes landfall south of West Palm Beach, or goes out to sea. No worries from Central Florida North Link to comment Share on other sites More sharing options...
Srain Posted July 31, 2011 Author Share Posted July 31, 2011 TROPICAL WEATHER OUTLOOK NWS NATIONAL HURRICANE CENTER MIAMI FL 200 PM EDT SUN JUL 31 2011 FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO... A LARGE AND ELONGATED LOW PRESSURE SYSTEM IS LOCATED ABOUT 575 MILES EAST OF THE NORTHERN WINDWARD ISLANDS. ALTHOUGH THIS SYSTEM HAS CHANGED LITTLE IN ORGANIZATION TODAY...ENVIRONMENTAL CONDITIONS ARE EXPECTED TO REMAIN CONDUCIVE FOR A TROPICAL DEPRESSION TO FORM LATER TODAY OR ON MONDAY. 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. AN AIR FORCE RESERVE UNIT RECONNAISSANCE AIRCRAFT IS EN ROUTE TO DETERMINE IF THIS BROAD DISTURBANCE HAS DEVELOPED A WELL-DEFINED SURFACE CIRCULATION CENTER. IF THE LOW BECOMES A TROPICAL CYCLONE LATER TODAY... TROPICAL STORM WATCHES OR WARNINGS WOULD LIKELY BE REQUIRED FOR PORTIONS OF THE NORTHERN WINDWARD ISLANDS AND THE LEEWARD ISLANDS. INTERESTS IN THESE AREAS SHOULD CLOSELY MONITOR THE PROGRESS OF THIS DEVELOPING SYSTEM. ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE NEXT 48 HOURS. $$ FORECASTER STEWART Link to comment Share on other sites More sharing options...
k*** Posted July 31, 2011 Share Posted July 31, 2011 Too bad last night's DMAX failed to get it over the hump Link to comment Share on other sites More sharing options...
wxmeddler Posted July 31, 2011 Share Posted July 31, 2011 Too bad last night's DMAX failed to get it over the hump The outflow band on the north side isn't a good sign either.. Link to comment Share on other sites More sharing options...
usedtobe 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. BUt there for MCS's correct. You certainly have system relative flow associated with them. See Parker and Johnson. That's part of the reason you get stratiform precip to the rear of forward propagating systems and to the front of backward propagating storms. Why wouldn't that also hold in the tropics? I guess I'm confused. Link to comment Share on other sites More sharing options...
OSUmetstud Posted July 31, 2011 Share Posted July 31, 2011 BUt there for MCS's correct. You certainly have system relative flow associated with them. See Parker and Johnson. That's part of the reason you get stratiform precip to the rear of forward propagating systems and to the front of backward propagating storms. Why wouldn't that also hold in the tropics? I guess I'm confused. 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. Link to comment Share on other sites More sharing options...
usedtobe Posted July 31, 2011 Share Posted July 31, 2011 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. They'd certainly know more than I would. I know for mCS the structure varies depending on the system relative flow. The structure is dependent on the system relative flow but that often is determined by the absolute shear but also on where the convergence is located relative to the system as that can slow or speed up the movements. I assumed for weaker circulations that were embedded and moving with the low level flow you could have the upper flow from the west even with east movement of the system which would increase the shear. But I'll cede the argument to NHC as they are certainly more up on the structure and dynamics than I am. Link to comment Share on other sites More sharing options...
hm8 Posted July 31, 2011 Share Posted July 31, 2011 12z GFDL and HWRF have a similar track north of the Bahamas, with the GFDL stronger Link to comment Share on other sites More sharing options...
wxmeddler Posted July 31, 2011 Share Posted July 31, 2011 Hey, we got G-IV dropsonde report north of Puerto Rico. Link to comment Share on other sites More sharing options...
eyewall Posted July 31, 2011 Share Posted July 31, 2011 NHC's thinking on the 1pm call was that the western complex is hindering the eastern complex's inflow...and the western complex is almost stationary so the eastern should merge with it as it moves west and then begin intensification in 18-24 hours. Looking at some hi-res vis it looks to me like the western complex is moving west...but I'm no expert This makes alot of sense so it may slow development in the short term until the western complex is absorbed. If it had a bit more space we would almost be looking at 2 invests at some point. Link to comment Share on other sites More sharing options...
dan88 Posted July 31, 2011 Share Posted July 31, 2011 12z GFDL and HWRF have a similar track north of the Bahamas, with the GFDL bringing it up to a borderline Cat 5 GFDL only brings the 10m winds up to 115kts and the pressure down to 952mb, which is a far cry from a cat 5. The wind chart you posted was for 900mb. Link to comment Share on other sites More sharing options...
Typhoon Tip Posted July 31, 2011 Share Posted July 31, 2011 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 problem there is that there is no difference. By "relative", what is meant is that storm motion negatively differentiates the impact force of opposing wind vectors, but shear its self is a scalar measure of what is impacting at any given time. In other words, the storm relative shear is going to be the same as the absolute shear - so it is ultimately pointless to make the comparison. Relative shear does not mean anything other than how the storm motion differentiates against the ambient wind field. Absolute shear is the value the cyclone is encountering regardless of how it encounters. Link to comment Share on other sites More sharing options...
jpeters3 Posted July 31, 2011 Share Posted July 31, 2011 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. 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 Link to comment Share on other sites More sharing options...
OSUmetstud 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? Yes, I see the point...I've gotten into arguments with others on this...I've never believed in the concept of "storm-relative shear"...which some mets think is relevant to tropical storms. Now I believe there is a very concept interaction between TCs and shear. It's not so simple as wind shear of 20 kt will be okay when 30 kt is not. I think the direction matters, and where the wind shear is located in the vertical It's shear btw, not sheer. Link to comment Share on other sites More sharing options...
am19psu Posted July 31, 2011 Share Posted July 31, 2011 Yes, I see the point...I've gotten into arguments with others on this...I've never believed in the concept of "storm-relative shear"...which some mets think is relevant to tropical storms. Now I believe there is a very concept interaction between TCs and shear. It's not so simple as wind shear of 20 kt will be okay when 30 kt is not. I think the direction matters, and where the wind shear is located in the vertical It's shear btw, not sheer. Agree with this strongly. Link to comment Share on other sites More sharing options...
jpeters3 Posted July 31, 2011 Share Posted July 31, 2011 They'd certainly know more than I would. I know for mCS the structure varies depending on the system relative flow. The structure is dependent on the system relative flow but that often is determined by the absolute shear but also on where the convergence is located relative to the system as that can slow or speed up the movements. I assumed for weaker circulations that were embedded and moving with the low level flow you could have the upper flow from the west even with east movement of the system which would increase the shear. But I'll cede the argument to NHC as they are certainly more up on the structure and dynamics than I am. 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 Link to comment Share on other sites More sharing options...
dan88 Posted July 31, 2011 Share Posted July 31, 2011 NHC's thinking on the 1pm call was that the western complex is hindering the eastern complex's inflow...and the western complex is almost stationary so the eastern should merge with it as it moves west and then begin intensification in 18-24 hours. Looking at some hi-res vis it looks to me like the western complex is moving west...but I'm no expert 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. Link to comment Share on other sites More sharing options...
jpeters3 Posted July 31, 2011 Share Posted July 31, 2011 Yes, I see the point...I've gotten into arguments with others on this...I've never believed in the concept of "storm-relative shear"...which some mets think is relevant to tropical storms. Now I believe there is a very concept interaction between TCs and shear. It's not so simple as wind shear of 20 kt will be okay when 30 kt is not. I think the direction matters, and where the wind shear is located in the vertical It's shear btw, not sheer. 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 Link to comment Share on other sites More sharing options...
usedtobe 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 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 Link to comment Share on other sites More sharing options...
jpeters3 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 we all need to learn somehow, and you wouldn't have if you hadn't "suck your head in this thread", so i'd say stick away! Link to comment Share on other sites More sharing options...
hurricaneman 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 Link to comment Share on other sites More sharing options...
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