wxsmwhrms Posted August 22, 2012 Share Posted August 22, 2012 Will be interested to see what NHC gives for motion and position on the next advisory. Hard to tell much from IR imagery, but the shortwave IR would tend to imply that there has not been much if any gain of latitude tonight. In fact, I might be tempted to think that there has been some reformation toward the better convection in the SW, but I know how deceiving it can be just looking at IR loops. Link to comment Share on other sites More sharing options...
Hurriplane Posted August 22, 2012 Share Posted August 22, 2012 18mph moving Due West. THERE HAS BEEN NO AERIAL RECONNAISSANCE INTO ISAAC RECENTLY...BUT THE CLOUD PATTERN OF THE STORM HAS NOT BECOME SIGNIFICANTLY BETTER ORGANIZED OVER THE PAST FEW HOURS. THE INTENSITY IS HELD AT 35 KT WHICH IS IN AGREEMENT WITH A DVORAK INTENSITY ESTIMATE FROM TAFB. ANOTHER HURRICANE HUNTER AIRCRAFT IS SCHEDULED TO INVESTIGATE ISAAC AT AROUND 0600 UTC. THERE IS SOME SPREAD IN CENTER FIXES...BUT BASED ON GEOSTATIONARY AND MICROWAVE IMAGERY THE INITIAL MOTION REMAINS ABOUT THE SAME...275/16. A WELL-DEFINED MID-TROPOSPHERIC RIDGE TO THE NORTH OF THE TROPICAL CYCLONE SHOULD MAINTAIN THE WESTWARD TRACK FOR THE NEXT COUPLE OF DAYS. LATER IN THE FORECAST PERIOD...GLOBAL MODELS DEPICT ISAAC NEARING A BREAK IN THE RIDGE NEAR FLORIDA. CONSEQUENTLY THE FORWARD SPEED IS LIKELY TO SLOW...AND THE HEADING TO GRADUALLY TURN TOWARD THE RIGHT...IN THE LATTER HALF OF THE FORECAST PERIOD. ALTHOUGH THE GFS HAS SHIFTED JUST A BIT TO THE NORTH OF ITS PREVIOUS FORECAST...OVERALL THE TRACK GUIDANCE HAS NOT CHANGED MUCH SINCE THE PREVIOUS CYCLE. THE OFFICIAL FORECAST IS VERY CLOSE TO THE LATEST HWRF TRACK AND NOT FAR FROM THE DYNAMICAL CONSENSUS. WATER VAPOR IMAGERY SUGGESTS THAT EAST-NORTHEASTERLY SHEAR IS CURRENTLY AFFECTING ISAAC...BUT THE DYNAMICAL GUIDANCE PREDICTS A DECREASE IN SHEAR WITH UPPER-LEVEL ANTICYCLONIC FLOW OVER THE TROPICAL CYCLONE DURING THE NEXT SEVERAL DAYS. THEREFORE STRENGTHENING IS ANTICIPATED...AND ISAAC COULD BECOME A HURRICANE WITHIN THE NEXT COUPLE OF DAYS. LATER ON...THE INTENSITY FORECAST IS COMPLICATED BY HOW MUCH THE CORE OF THE SYSTEM INTERACTS WITH THE MOUNTAINOUS LAND MASSES OF HISPANIOLA AND EASTERN CUBA. THE OFFICIAL WIND SPEED FORECAST IS FAIRLY CLOSE TO THE STATISTICAL- DYNAMICAL GUIDANCE FOR THE FIRST 48 HOURS AND THEN TRIES TO TAKE INTO ACCOUNT THE LAND INTERACTION. NEEDLESS TO SAY...THERE IS CONSIDERABLE UNCERTAINTY IN THE INTENSITY OF ISAAC IN THE 3 TO 5 DAY TIME FRAME. FORECAST POSITIONS AND MAX WINDS INIT 22/0300Z 15.6N 55.6W 35 KT 40 MPH 12H 22/1200Z 15.8N 58.1W 40 KT 45 MPH 24H 23/0000Z 16.2N 61.2W 45 KT 50 MPH 36H 23/1200Z 16.7N 64.3W 55 KT 65 MPH 48H 24/0000Z 17.1N 67.1W 65 KT 75 MPH 72H 25/0000Z 18.3N 72.0W 65 KT 75 MPH...INLAND 96H 26/0000Z 20.5N 76.0W 70 KT 80 MPH...INLAND 120H 27/0000Z 23.0N 79.0W 70 KT 80 MPH...OVER WATER Link to comment Share on other sites More sharing options...
MJO812 Posted August 22, 2012 Share Posted August 22, 2012 11pm cone. Shifted slightly north east. Link to comment Share on other sites More sharing options...
Hurriplane Posted August 22, 2012 Share Posted August 22, 2012 11pm cone. Shifted slightly north east. I'm still a little baffled with the NHC intensity once it reaches the mountains.. Link to comment Share on other sites More sharing options...
OHweather Posted August 22, 2012 Share Posted August 22, 2012 I'm still a little baffled with the NHC intensity once it reaches the mountains.. My guess is that at this point the amount of land interaction is uncertain...this combined with the NHC track would result in Isaac missing the worst of the mountains, that the circulation wouldn't spend extended periods of time over land, and that a large portion of the circulation would be over water given the relatively small size of the islands is likely why the NHC maintains Isaac as a hurricane later in the forecast period. Link to comment Share on other sites More sharing options...
turtlehurricane Posted August 22, 2012 Share Posted August 22, 2012 Very cold cloud tops going up, big convective burst. Looks like a significant band is about to sweep through the Lesser Antilles as well, might be a good time to start monitoring the Caribbean hurricane network. http://stormcarib.com/ Link to comment Share on other sites More sharing options...
Windspeed Posted August 22, 2012 Share Posted August 22, 2012 I'm still a little baffled with the NHC intensity once it reaches the mountains.. The intensity is not based on the center line of the track guidance. As detailed in the discussion, the intensity forecast is highly unpredictable because a few degrees north or south can be the difference between the core crossing over a high range or missing that range entirely; therefore, they keep it a catagory one hurricane. Obivously, if the core traverses a greater portion of Hispanola, it has a greater chance of weakening into a tropical storm. Forward motion is also a factor. And if the storm is in a very favorable environment with little to no shear, that will help it hold together during that process. It takes more than just the high terrain of Hispanola to completely dismantle a hurricane. And then of course, what if the core missed the island entirely? The NHC would be unwise to include a downgrade in status that far out based on such approximations. Link to comment Share on other sites More sharing options...
Analog96 Posted August 22, 2012 Share Posted August 22, 2012 I'm still a little baffled with the NHC intensity once it reaches the mountains.. Because on that track, the storm doesn't really cross too many mountains. It really is mostly over coastal terrain of Haiti and Cuba Link to comment Share on other sites More sharing options...
turtlehurricane Posted August 22, 2012 Share Posted August 22, 2012 Also a good time to check out the Barbados radar, page seems upgraded or maybe I'm behind the times: http://www.barbadosw...ather-radar.php Link to comment Share on other sites More sharing options...
Derecho! Posted August 22, 2012 Share Posted August 22, 2012 I'm still a little baffled with the NHC intensity once it reaches the mountains.. The thing is, NHC's goal is to minimize the error of the intensity forecast (and rightly so). And the intensity forecast can't be based off the precise forecast track, since that has error. That's the same reason NHC issues a lot of forecasts for tropical storms with a smooth 5-10 kts of strengthening between forecast positions, when actual TC strengthening (in the Atlantic) almost never actually happens that way. But those sorts of forecasts help to eliminate really egregious intensity forecast errrors. The reality for the back end of the Isaac Intensity forecast is that at, say, 96 hours, it's probably much more likely to either be at 50 knots or 100 knots than the forecast 70 knots.But it's not a smart move to pick one of the extremes. Link to comment Share on other sites More sharing options...
phil882 Posted August 22, 2012 Share Posted August 22, 2012 Looks like the 00z GFS is going to come in a little further north... ridging is not as strong this run in the early going. Link to comment Share on other sites More sharing options...
PSUBlizzicane2007 Posted August 22, 2012 Share Posted August 22, 2012 Looks like the 00z GFS is going to come in a little further north... ridging is not as strong this run in the early going. If this does happen... I will be quite interested to see if it shifts back west at 12Z. I vaguely remember last year and/or the year before that models would shift right at 00Z and left at 12Z...as if, perhaps, there is some sort of diurnal feedback from the initial conditions causing small shifts. Link to comment Share on other sites More sharing options...
andyhb Posted August 22, 2012 Share Posted August 22, 2012 If this does happen... I will be quite interested to see if it shifts back west at 12Z. I vaguely remember last year and/or the year before that models would shift right at 00Z and left at 12Z...as if, perhaps, there is some sort of diurnal feedback from the initial conditions causing small shifts. Glad I wasn't the only one to notice something along these lines. Link to comment Share on other sites More sharing options...
Marion_NC_WX Posted August 22, 2012 Share Posted August 22, 2012 0z GFS at 132 hours showing a 992mb storm coming into South Florida and moving WNW to NW. Link to comment Share on other sites More sharing options...
wxmeddler Posted August 22, 2012 Share Posted August 22, 2012 Air Force Recon is in the air for the 6z and 12z fixes. Things to look out for is symmetry/stacking between the convective patterns and the wind field at flight level and any dropsondes they release. Also as well as any decrease in pressure from the recent convection and whether this is from a new Central Dense Overcast (CDO) development (slight core banding?) or a Diurnal-Maximum temporary burst. Link to comment Share on other sites More sharing options...
SN_Lover Posted August 22, 2012 Share Posted August 22, 2012 The path of the 0Z GFS looks very irregular right before FL. Link to comment Share on other sites More sharing options...
Marion_NC_WX Posted August 22, 2012 Share Posted August 22, 2012 The one trend I have noticed throughout the day Tuesday has been for the models to really slow down the forward movement of this storm once is comes close or ashore Florida... Link to comment Share on other sites More sharing options...
Typhoon Tip Posted August 22, 2012 Share Posted August 22, 2012 Air Force Recon is in the air for the 6z and 12z fixes. Things to look out for is symmetry/stacking between the convective patterns and the wind field at flight level and any dropsondes they release. Also as well as any decrease in pressure from the recent convection and whether this is from a new Central Dense Overcast (CDO) development (slight core banding?) or a Diurnal-Maximum temporary burst. I am not seeing a CDO here, but perhaps you are inferring that there may be a center jump SW of the current fix? Sure that's possible. By definition it needs to surround the core axis of rotation, which apparently is not happening given current fix. But, center jumps in early TCs is not that uncommon; I have noticed in weakly sheared systems that multiple center jumps can take place as the mid level UVM/cyclonic core cyclically works back down to the surface. Link to comment Share on other sites More sharing options...
phil882 Posted August 22, 2012 Share Posted August 22, 2012 Air Force Recon is in the air for the 6z and 12z fixes. Things to look out for is symmetry/stacking between the convective patterns and the wind field at flight level and any dropsondes they release as well as any decrease in pressure from the recent convection and whether this is from a new Central Dense Overcast (CDO) development (slight core banding?) or a D-Max temporary burst. Its very difficult to tell if the center is shifting under the convection and organizing or if its still partially exposed. My hunch is the latter. Link to comment Share on other sites More sharing options...
Analog96 Posted August 22, 2012 Share Posted August 22, 2012 Its very difficult to tell if the center is shifting under the convection and organizing or if its still partially exposed. My hunch is the latter. Most likely, considering that it's still a weak storm. Link to comment Share on other sites More sharing options...
wxmeddler Posted August 22, 2012 Share Posted August 22, 2012 I am not seeing a CDO here, but perhaps you are inferring that there may be a center jump SW of the current fix? Sure that's possible. By definition it needs to surround the core axis of rotation, which apparently is not happening given current fix. But, center jumps in early TCs is not that uncommon; I have noticed in weakly sheared systems that multiple center jumps can take place as the mid level UVM/cyclonic core cyclically works back down to the surface. Oh I agree that there is no CDO here, not even close, but I was bringing up that there is a possibility that this convective pulse might be the beginnings of (with help of D-Max) a CDO establishing itself going into tomorrow. My belief however that it is most likely just regular D-Max helping and convection should wane by mid-morning storm local time. That's just me though, have to wait and see and maybe get a hint of whats going on with the recon fix. On the LLC topic, a center jump is certainly possible, but with the large area of momentum that has to be re-directed slightly to do that in the low levels, I think that in this case, it is unlikely or would take a long time for a center relocation to happen. Link to comment Share on other sites More sharing options...
Superstorm93 Posted August 22, 2012 Share Posted August 22, 2012 Still a heavy bursting pattern over the LLC. Not too surprised since this is just a 40 mph tropical storm. I think we'll see the typical diurnal cycles prevail for the next day or so. Link to comment Share on other sites More sharing options...
gulfcane Posted August 22, 2012 Share Posted August 22, 2012 The GFS track is full of peril, regardless of how strong it shows the system. It gets tangled in Hispaniola pretty good and then wallows around cuba forever. It's possible to get as strong as the GFS shows on that track, but it would be a very delicate balance. That run is giving me nightmares of 2008 F*Y. It just loved to hop islands and take a full tour for days. I still think it is likely to skirt south of Hispaniola or maybe just scrap it briefly without damaging the core too much. Ultimately the islands are positioned in such a way that even a small deviation of track is the difference between landfall for days or not at all. Link to comment Share on other sites More sharing options...
MJO812 Posted August 22, 2012 Share Posted August 22, 2012 0z GEFS took a big leap to the east. Link to comment Share on other sites More sharing options...
SN_Lover Posted August 22, 2012 Share Posted August 22, 2012 wxrisk.com made this point about the 0z GFS run in comparison to Euro which i think is a good argument to make. Link to comment Share on other sites More sharing options...
Minnesota Meso Posted August 22, 2012 Share Posted August 22, 2012 0z GEFS took a big leap to the east. Can't show it yet, but the GEM looks some what similar...of course much deeper as it want's to do with each tropical system it sniffs Link to comment Share on other sites More sharing options...
phil882 Posted August 22, 2012 Share Posted August 22, 2012 Recon finding quite a convoluted Isaac at this point... little to no wind on the SW flank of the circulation, with multiple wind reversals. This seems somewhat similar to the Ernesto debacle, where the low level circulation actually became less defined when the convection was firing all around it, causing the low-level wind pattern to be chaotic. Link to comment Share on other sites More sharing options...
Minnesota Meso Posted August 22, 2012 Share Posted August 22, 2012 wxrisk.com made this point about the 0z GFS run in comparison to Euro which i think is a good argument to make. interesting indeed Link to comment Share on other sites More sharing options...
wxmeddler Posted August 22, 2012 Share Posted August 22, 2012 Can't show it yet, but the GEM looks some what similar...of course much deeper as it want's to do with each tropical system it sniffs I've always been a proponent of the "teach a man to fish" philosophy.. The GEFS is almost always going to be of a lower strength because it is the mean of all of the GFS Ensembles. How ensembles work is taking the initial conditions and altering them slightly in different ways so that each ensemble will represent non-perfect starting positions because since there's no perfect observation network (especially over the ocean). The ensembles represent the, more or less "range" of potential scenarios/ outcomes. The main models (GFS,ECMWF,CMC etc.) only run one scenario, the "best guess" scenario, and run it at a much higher detail than the ensembles and thus the pressures will be lower and the picture "more complete/better" than the ensemble mean. The fact that the low is 1001mb on the GEFS is pointing to the fact that there is fairly high certainty amongst the ensemble members that the cyclone will be near that point and in fact looking at each of the individual ensemble members of the 0z run. They are! Link to individual member loop Link to comment Share on other sites More sharing options...
dan88 Posted August 22, 2012 Share Posted August 22, 2012 850mb center, 15.5N, 56.7W, 1003.5mb extrap Link to comment Share on other sites More sharing options...
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