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Extratropical Depression Lee


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One again a pretty interesting evolution from the ECWMF, but I'm not sure I'd go for the long range stalling solution just yet... The key seems to be that the ECWMF takes 93L significantly further west in the short term than the GFS, so the strength of the ridging over the next 48 hours will be key to see if this system gets picked up by the mid-latitude trough or if its left behind in the GOM if it manages to move further west than the GFS solution.

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Variance in the statistical track guidance suggests GFS may be forecasting unfavorable shear.

933   

WHXX01 KWBC 311850  

CHGHUR  

TROPICAL CYCLONE GUIDANCE MESSAGE  

NWS NATIONAL HURRICANE CENTER MIAMI FL  

1850 UTC WED AUG 31 2011  

DISCLAIMER...NUMERICAL MODELS ARE SUBJECT TO LARGE ERRORS.  

PLEASE REFER TO NHC OFFICIAL FORECASTS FOR TROPICAL CYCLONE  

AND SUBTROPICAL CYCLONE INFORMATION.  



ATLANTIC OBJECTIVE AIDS FOR  



DISTURBANCE INVEST (AL932011) 20110831 1800 UTC  



       ...00 HRS...   ...12 HRS...   ...24 HRS. ..   ...36 HRS...  

       110831  1800   110901  0600   110901  1800   110902  0600  



        LAT    LON     LAT    LON     LAT    LON     LAT    LON  

BAMS    24.1N  87.0W   25.3N  89.2W   26.5N  91.4W   27.1N  93.1W  

BAMD    24.1N  87.0W   25.0N  88.3W   25.9N  89.4W   26.6N  90.3W  

BAMM    24.1N  87.0W   25.2N  88.8W   26.2N  90.5W   26.9N  91.8W  

LBAR    24.1N  87.0W   25.2N  88.4W   26.4N  89.8W   27.4N  91.0W  

SHIP        30KTS          35KTS          42KTS          50KTS  

DSHP        30KTS          35KTS          42KTS          50KTS  



       ...48 HRS...   ...72 HRS...   ...96 HRS. ..   ..120 HRS...  

       110902  1800   110903  1800   110904  1800   110905  1800  



        LAT    LON     LAT    LON     LAT    LON     LAT    LON  

BAMS    27.6N  94.5W   26.9N  96.4W   24.9N  98.0W   23.0N 101.1W  

BAMD    27.3N  90.8W   28.3N  90.9W   28.9N  91.2W   28.9N  91.0W  

BAMM    27.5N  92.9W   27.1N  93.6W   25.8N  91.4W   28.2N  88.3W  

LBAR    28.3N  92.0W   29.0N  93.1W   29.1N  94.1W   29.0N  94.8W  

SHIP        59KTS          69KTS          73KTS          71KTS  

DSHP        59KTS          69KTS          73KTS          71KTS  



        ...INITIAL CONDITIONS...  

LATCUR =  24.1N LONCUR =  87.0W DIRCUR = 320DEG SPDCUR =   8KT  

LATM12 =  22.5N LONM12 =  85.5W DIRM12 = 320DEG SPDM12 =  14KT  

LATM24 =  19.8N LONM24 =  83.0W  

WNDCUR =   30KT RMAXWD =   75NM WNDM12 =   25KT  

CENPRS = 1012MB OUTPRS = 1014MB OUTRAD =  100NM SDEPTH =   S  

RD34NE =    0NM RD34SE =    0NM RD34SW =    0NM RD34NW =   0NM  



$$  

NNNN  

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I really think a combined GFS/Euro solution is in the works for 93L... in that there will be a westwardness to 93L initially, but I believe the trough that is coming later in the period is being underforecasted by the Euro... albeit the 12Z run seems more eager for 93L to be "sensed" by the trough as it gets pulled northward into Texas versus the 00Z run.

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I imagine the intensity of 93L will be highly track-dependent. If it stalls it will upwell itself to death. It if gets caught it will remain in a high-shear regime until landfall. The 12Z Euro scenario of getting trapped under the ridge and heading SW may be the best scenario for the storm as upper level conditions improve over time.

P.S. If I were to pick a track right now I'd favor the Euro track.

1) The Euro has the best track record of all models and the best handle on midlatitude features. I don't think any prior run of the Euro had 93L turning northeastward (correct me if I'm wrong).

2) Based on persistence the Southern U.S. ridge will [again] be stronger than progged.

3) Because of the initial shear and perhaps upwelling, 93L should remain weak until it makes that turn (at the earliest), which disfavors the more poleward track.

4) 93L is a pretty large system. Progressive troughs tend to have a more difficult time completely recurving large, bulky TC's.

But again this is very low confidence and I could definitely see the NE turn happen as well.

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Variance in the statistical track guidance suggests GFS may be forecasting unfavorable shear.

933   

WHXX01 KWBC 311850  

CHGHUR  

TROPICAL CYCLONE GUIDANCE MESSAGE  

NWS NATIONAL HURRICANE CENTER MIAMI FL  

1850 UTC WED AUG 31 2011  

DISCLAIMER...NUMERICAL MODELS ARE SUBJECT TO LARGE ERRORS.  

PLEASE REFER TO NHC OFFICIAL FORECASTS FOR TROPICAL CYCLONE  

AND SUBTROPICAL CYCLONE INFORMATION.  



ATLANTIC OBJECTIVE AIDS FOR  



DISTURBANCE INVEST (AL932011) 20110831 1800 UTC  



       ...00 HRS...   ...12 HRS...   ...24 HRS. ..   ...36 HRS...  

       110831  1800   110901  0600   110901  1800   110902  0600  



        LAT    LON     LAT    LON     LAT    LON     LAT    LON  

BAMS    24.1N  87.0W   25.3N  89.2W   26.5N  91.4W   27.1N  93.1W  

BAMD    24.1N  87.0W   25.0N  88.3W   25.9N  89.4W   26.6N  90.3W  

BAMM    24.1N  87.0W   25.2N  88.8W   26.2N  90.5W   26.9N  91.8W  

LBAR    24.1N  87.0W   25.2N  88.4W   26.4N  89.8W   27.4N  91.0W  

SHIP        30KTS          35KTS          42KTS          50KTS  

DSHP        30KTS          35KTS          42KTS          50KTS  



       ...48 HRS...   ...72 HRS...   ...96 HRS. ..   ..120 HRS...  

       110902  1800   110903  1800   110904  1800   110905  1800  



        LAT    LON     LAT    LON     LAT    LON     LAT    LON  

BAMS    27.6N  94.5W   26.9N  96.4W   24.9N  98.0W   23.0N 101.1W  

BAMD    27.3N  90.8W   28.3N  90.9W   28.9N  91.2W   28.9N  91.0W  

BAMM    27.5N  92.9W   27.1N  93.6W   25.8N  91.4W   28.2N  88.3W  

LBAR    28.3N  92.0W   29.0N  93.1W   29.1N  94.1W   29.0N  94.8W  

SHIP        59KTS          69KTS          73KTS          71KTS  

DSHP        59KTS          69KTS          73KTS          71KTS  



        ...INITIAL CONDITIONS...  

LATCUR =  24.1N LONCUR =  87.0W DIRCUR = 320DEG SPDCUR =   8KT  

LATM12 =  22.5N LONM12 =  85.5W DIRM12 = 320DEG SPDM12 =  14KT  

LATM24 =  19.8N LONM24 =  83.0W  

WNDCUR =   30KT RMAXWD =   75NM WNDM12 =   25KT  

CENPRS = 1012MB OUTPRS = 1014MB OUTRAD =  100NM SDEPTH =   S  

RD34NE =    0NM RD34SE =    0NM RD34SW =    0NM RD34NW =   0NM  



$$  

NNNN  

I would point out that the wording in the TWO would imply that NHC is thinking there may be a subtropical nature to the development. All of the models are certainly pretty bullish now on deepening the system.

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I would point out that the wording in the TWO would imply that NHC is thinking there may be a subtropical nature to the development. All of the models are certainly pretty bullish now on deepening the system.

It's fair enough for them to point that out with the ULL sitting there... but in the end, this is more likely than not to be tropical.

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NATIONAL WEATHER SERVICE BROWNSVILLE TX 215 PM CDT WED AUG 31 2011

.SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/...THERE IS POTENTIAL FOR CYCLONE DEVELOPMENT IN THE CENTRAL AND WESTERN GULF WITHIN A FEW DAYS ACCORDING TO THE NATIONAL HURRICANE CENTER...WITH A 30 PERCENT CHANCE OF SOMETHING FORMING IN THE NEXT 48 HOURS. THE PREFERRED NWP MODEL IS STILL THE ECMWF WHEN TRANSITIONING FROM THE SHORT TERM TO THE LONG TERM. FOR NOW... BY THE END OF THE SHORT TERM...CONVECTION ASSOCIATED WITH A TROPICAL WAVE WILL DEVELOP IN THE CENTRAL GULF...AND A CYCLONIC CIRCULATION IN THE WEST OR NORTHWEST GULF WILL OVERRIDE TROUGHING ALONG THE NORTHEAST MEXICAN COAST.

.LONG TERM /FRIDAY THROUGH TUESDAY/...THE WIDE RANGE OF SOLUTIONS FOR THE UPCOMING WEEKEND...FROM ABSOLUTELY NOTHING TO FULLY CLOSED OFF TROPICAL CYCLONE...LEAVES SIGNIFICANT DOUBT AS TO A FINAL SOLUTION FOR THE LABOR DAY WEEKEND. MODELS ARE TRYING TO WRAP THIS SYSTEM UP IN THE NW GULF OVER THE WEEKEND...BUT MODELS ARE COMPLETELY APART ON WHICH DIRECTION IS MOVING...AND ARE CHANGING RUN TO RUN...SO FORECAST CONFIDENCE IS VERY LOW. MOST MODELS DO AGREE THAT WINDS WILL BE ELEVATED FOR THE WEEKEND FROM THE NORTH. THIS WOULD LEAD TO SIGNIFICANT INCREASE IN RIP CURRENT RISK AND INCREASING CHANCES OF SOME COASTAL FLOODING OCCURRING FOR THE WEEKEND. HIGH PRESSURE REMAINS ANCHORED ACROSS THE LOWER MISSISSIPPI VALLEY INTO WEST TEXAS...WHILE STRONG MIDLEVEL TROUGH CUTS NE TO SW ACROSS THE GULF. THE RIDGE IS EXPECTED TO STRENGTHEN NEAR THE MOUTH OF THE MISSISSIPPI...WHICH WOULD HELP ENHANCE THE GULF WAVE. DRY AIR WRAPPING IN FROM THE NORTH ON FRIDAY WILL KEEP THE FORECAST MAINLY DRY...WITH TEMPS AGAIN SOARING ABOVE 100 DEGREES. MOISTURE LOOKS TO RETURN OVER THE WEEKEND ENOUGH TO SPARK SHOWERS AND THUNDERSTORMS...WITH SOME HEAVY DOWNPOURS EXPECTED. AGAIN...KEEP A WATCH ON THE LATEST NWS FORECAST FOR THE WEEKEND AS THE FORECAST COULD CHANGE RAPIDLY UNTIL THEN.

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It's fair enough for them to point that out with the ULL sitting there... but in the end, this is more likely than not to be tropical.

Agreed. And I agree with phil882 about the ECMWF - it seems to be trending more toward the idea of it getting picked up by the trough even though it just misses it in the actual operational run, and that is a solution that would be more favored climatologically.

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:rolleyes:

It's fair enough for them to point that out with the ULL sitting there... but in the end, this is more likely than not to be tropical.

And if it doesn't have 100% tropical characteristics to start initially, water temps of some 32C will remedy that rather quickly....And I wouldn't overplay the upwelling too much at this time, regarding a stall....we are at peak annual SST for down there, we haven't had an apppreciable storm down there, and anomolies are quite positive. Coupled with that we still have a few days of modeling to go prior to any stall...and the area that the storm would have to reside to be left hangin' is not very large. I'd think N. O. and points west along to the extreme NE TX coast should prepare for copious rainfall due to a slowly drifting (maybe a little loop) strong TS or weak Cat 1...

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Agreed. And I agree with phil882 about the ECMWF - it seems to be trending more toward the idea of it getting picked up by the trough even though it just misses it in the actual operational run, and that is a solution that would be more favored climatologically.

Yup, and that was what I was mentioning in my post above... granted the GFS is faster than the Euro (shock), but since the Euro is trending to the idea of it being picked up, I have to go with some combination of the two.... both an average in terms of speed and eventual location of landfall.

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The worst possible thing that could happen would be a stall that just eats up OHC without producing something good.

A stall just off shore Texas that drops a foot of rain over a 5 day period at my house with little sea level rise would actually be the best thing ever. Doubt it happens, however.

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A stall just off shore Texas that drops a foot of rain over a 5 day period at my house with little sea level rise would actually be the best thing ever. Doubt it happens, however.

I have to agree. I'd take a Cat 1 if it meant some good rains...but the absolute worst possible thing for my pals down on Galveston would be what some consider "something good".

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Yup, and that was what I was mentioning in my post above... granted the GFS is faster than the Euro (shock), but since the Euro is trending to the idea of it being picked up, I have to go with some combination of the two.... both an average in terms of speed and eventual location of landfall.

Agreed. I did find one robust system that behaved in at least a manner somewhat like what some of the models are showing as far as movement back to the SW, though.

http://en.wikipedia.org/wiki/Hurricane_Fern_(1971)

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Weenie comment and doubt it will happen, but I hope this slams into SW TX coast and rains like crazy from the coast to Austin west to West Texas. Can't describe how bad we need the rain. We are only down to one water source at this point. Hopefully it will be big enough to help Houston etc. also.

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Looks to me like this will form somewhere south of LA- then it is a knife edge on whether it gets picked up and moves east or NE like the GFS says or will it miss the trough as the majority of the guidance has and then move back W or SW to Texas. The latter scenario seems a bit more likely right now, but until something actually forms we will likely get a few more twists and turns from the models.

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12z experimental GFS/ENKF ensembles are pretty well clustered around the north central gulf coast. I am not sure how reliable this is though.

I've heard from someone involved in EnKF TC modeling that the GFS/EnKF ensembles are quite good, much better than the operational GFS ensembles, and perhaps even in the same breath as the ECMWF ensembles. This is second-hand info though, and these are experimental.

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Looks to me like this will form somewhere south of LA- then it is a knife edge on whether it gets picked up and moves east or NE like the GFS says or will it miss the trough as the majority of the guidance has and then move back W or SW to Texas. The latter scenario seems a bit more likely right now, but until something actually forms we will likely get a few more twists and turns from the models.

Agreed, except I might slightly lean toward your former solution just due to climatology and experience which suggests that model forecasts of stalling TCs along the Gulf Coast happen less frequently than the models forecast them. In any event, the 12Z EC ensemble mean is almost on top of the operational through day 5. Then the spread looks to increase dramatically with one cluster probably taking the system NE toward PNS and the other system SW toward BRO, and just based on the depth in the mean probably a few more robust members are on the SW solution of the ops than on the NE solution.

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