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Tropical Storm Isaac, Part 1: Moving Through The Eastern Caribbean Sea


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I tend to agree, although I won't be surprised to see actual development further W in the Caribbean. Are tropical storm conditions likely in the Antilles? Probably. The EC ensembles are rather insistent that the NW Caribbean will be the area to watch for more aggressive development early next week.

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ADT is fairly useless for developing tropical storms, and Dvorak of any kind is extra-irrelvant when recon is present.

FYP a little bit. ADT is great when there is a cleared out eye. SATCON is a much better intensity absent recon. Of course, you are right about recon being the final arbiter.

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Wouldn't consider that a major shift it's been back and forth with east coast and west for days now.

Yeah... The only MAJOR difference I see is the 6Z is a bit slower and taking it through the Florida Straits (after making a nice jog west over northern Cuba) instead of up the spine of the state or Everglades to get to the west coast.

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As the Euro strings multiple, consistent runs together with rather large entities, it's difficult, IMO, to NOT continue to increase one's confidence in the general solution. That does NOT mean we won't see a bit of a minor shift back to the right. Large system + consistant runs of top performing model + waffling of other models = growing GOM threat.

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Yeah... The only MAJOR difference I see is the 6Z is a bit slower and taking it through the Florida Straits (after making a nice jog west over northern Cuba) instead of up the spine of the state or Everglades to get to the west coast.

Don't know that I would term it a major difference at that time frame either, but it definitely did noticeable shift to the left and is quicker. A number of its ensemble members on the 06Z run are now almost as far left as the op EC.

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As the Euro strings multiple, consistent runs together with rather large entities, it's difficult, IMO, to NOT continue to increase one's confidence in the general solution. That does NOT mean we won't see a bit of a minor shift back to the right. Large system + consistant runs of top performing model + waffling of other models = growing GOM threat.

Can you explain your comment re: EC consistency vs. the 5am disco?

THE NHC MODEL

GUIDANCE IS IN EXCELLENT AGREEMENT ON THIS EVOLVING SCENARIO WITH

THE ECMWF BEING THE LEFTMOST OF THE MODELS...AND THE GFDL AND HWRF

BEING THE RIGHTMOST OF THE MODELS. GIVEN THE RUN-TO-RUN CONSISTENCY

OF THE GFS AND UKMET MODELS...MORE WEIGHT HAS BEEN PLACED ON THOSE

SOLUTIONS...ESPECIALLY SINCE THEY HAVE A STRONGER AND VERTICALLY

DEEPER CYCLONE DEPICTED IN THE MODELS.

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Can you explain your comment re: EC consistency vs. the 5am disco?

THE NHC MODEL

GUIDANCE IS IN EXCELLENT AGREEMENT ON THIS EVOLVING SCENARIO WITH

THE ECMWF BEING THE LEFTMOST OF THE MODELS...AND THE GFDL AND HWRF

BEING THE RIGHTMOST OF THE MODELS. GIVEN THE RUN-TO-RUN CONSISTENCY

OF THE GFS AND UKMET MODELS...MORE WEIGHT HAS BEEN PLACED ON THOSE

SOLUTIONS...ESPECIALLY SINCE THEY HAVE A STRONGER AND VERTICALLY

DEEPER CYCLONE DEPICTED IN THE MODELS.

PRELIMINARY EXTENDED FORECAST DISCUSSION

NWS HYDROMETEOROLOGICAL PREDICTION CENTER COLLEGE PARK MD

348 AM EDT WED AUG 22 2012

VALID 12Z SUN AUG 26 2012 - 12Z WED AUG 29 2012

THE JET STREAM IS EXPECTED TO REMAIN SPLIT THROUGH THE UPCOMING

MEDIUM RANGE PERIOD...WITH ONE BRANCH EXTENDING FROM ALASKA TO

SOUTHERN ONTARIO/QUEBEC...AND ANOTHER SMALLER BRANCH ACCOMPANYING

A CLOSED LOW THAT DRIFTS INTO PACIFIC NORTHWEST. OVER THE

REMAINDER OF THE CONUS...A CORRESPONDING UPPER HIGH SHOULD BUILD

OVER THE CENTRAL/SOUTHERN ROCKIES...WHILE A BROAD WEAKNESS IN

MID/UPPER LEVEL HEIGHTS LINGERS OVER THE EAST COAST. DESPITE THE

COMPLICATED SHORTWAVE PATTERN EMBEDDED WITHIN THE LONGWAVE

FLOW...MODEL AGREEMENT IS QUITE GOOD THROUGH ABOUT DAY

4/SAT...WITH ALMOST ANY SOLUTION QUITE GOOD...EXCEPT FOR PERHAPS

OVER SASKATCHEWAN/ONTARIO WITH THE 00Z GFS SUSPICIOUSLY QUICK AND

APPEARING TO SUFFER FROM CONVECTIVE GRID-SCALE FEEDBACK.

BEGINNING WITH DAY 5/SUN HOWEVER...THE SPREAD QUICKLY INCREASES

PARTICULARLY WITH THE NORTHERN BRANCH OF THE JET CROSSING

CANADA...WITH THE GFS THE FIRST SOLUTION TO DEVIATE MOST FROM THE

CONSENSUS AND THUS LESS PREFERRED COMPARED TO THE 00Z ECMWF AND

ITS OWN ENSEMBLE MEAN...WHICH WILL FORM THE BASIS OF THE

PRELIMINARY PRESSURES/FRONT. REGARDING TS ISAAC...THE SOLUTION

SPREAD IS EXTREMELY LARGE...WITH THE 00Z CANADIAN THE FIRST TO

CURVE ISAAC TO THE NORTH...BRINGING ISAAC TOWARD MYRTLE BEACH BY

NEXT MONDAY...

WHILE THE GFS/UKMET AFFECT SOUTHERN FLORIDA...AND ECMWF ACROSS

WESTERN CUBA BEFORE ENTERING THE GULF OF MEXICO. WILL USE THE

LATEST POINTS RELAYED IN THE 08Z COORDINATION CALL WITH THE NHC

FOR DAYS 3-5...BEFORE BLENDING DAYS 6/7 WITH YESTERDAY'S

COORDINATED POINTS. REFER TO THE NHC FOR THE LATEST FORECAST FOR

TS ISAAC.

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Can you explain your comment re: EC consistency vs. the 5am disco?

THE NHC MODEL

GUIDANCE IS IN EXCELLENT AGREEMENT ON THIS EVOLVING SCENARIO WITH

THE ECMWF BEING THE LEFTMOST OF THE MODELS...AND THE GFDL AND HWRF

BEING THE RIGHTMOST OF THE MODELS. GIVEN THE RUN-TO-RUN CONSISTENCY

OF THE GFS AND UKMET MODELS...MORE WEIGHT HAS BEEN PLACED ON THOSE

SOLUTIONS...ESPECIALLY SINCE THEY HAVE A STRONGER AND VERTICALLY

DEEPER CYCLONE DEPICTED IN THE MODELS.

5am discussion was produced before 06z GFS output, which certainly came left a good bit. As far as the UK...I need to see it remain consistent longer before I give it as much value as th Euro. As is usually the case, the strength of the ridge as modeled will be the lagest factor in determining the general track/speed.

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I think Easterly shear is abating, I am starting to see some of that feathery cirrus outflow to the Northeast. Could be a good sign.

Per the end of the recon it's still an organizational disaster, amazingly....though the advisory stayed with 1004 mb the last vortex was 1007 mb.

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Per the end of the recon it's still an organizational disaster, amazingly....though the advisory stayed with 1004 mb the last vortex was 1007 mb.

Quite similar to Ernesto in the eastern Carib. Will be interesting to see how quickly it comes together once past the leewards.

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20120822.0952.coriolis.37pct37h37v.09L.ISAAC.40kts.1003mb.15.5N.56.5W.90pc.jpg

Latest Windsat still shows Isaac looking disorganized. The main area of cold cloud tops in the IR is that banded area of pink (deep convection) almost directly to the south of the center. A second banding area to the east of the center is trying to form but the latest IR indicates that this area of convection has died out. I think only slow intensification will occur today, it isn't going to do much until some rainbands form on the NW side. Usually there is southwesterly shear in this region, it is different to see a northerly/easterly shear signature on microwave.

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Although these products lag by a half day vs. other outputs the GFS/EnKF tracks have trended left:

ellipses_2012082106_09L.gif

ellipses_2012082118_09L.gifellipses_2012082112_09L.gif

what is odd is that all those runs take Isaac to roughly the same exit point on Cuba at day 5. After that is where it diverges. I was under the impression that the ridge would break down after that, and not strengthen and move Isaac to the left. Am I misinformed there? Also, it really is a different solution than the Euro, and not really a movement toward the Euro since the Euro has the storm moving through the Yucatan channel.

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Here's the root page, proceed from there:

http://www.esrl.noaa...fsenkf/control/

Just some other background on this....this is a higher resolution deterministic run (T878, ~20 km or so?....I need to check the numbers) than our operational GFS (T574, ~27km), but utilizing similar phyics (for better or worse, untuned) and a comparable DA scheme (they are using an all out EnKF, whereas our operational DA is a hybrid EnKF/Var system). The ensemble is run at T382L64 (centered about the T878 EnKF analysis) versus the operational GEFS which is T254L42 (which uses a much more simplistic ensemble perturbation initialization technique). It's all experimental, but is sort of a proving ground for stuff we are thinking about for future operations (though we are actually working on even higher spatial resolution for the GFS with different dynamics [semi-Lagrangian instead of Eulerian] and tuned phyics ).

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