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Remnant low Karen


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 The 6Z GFS, which ends up hitting Apalachicola Sunday afternoon with its strongest run yet on the low resolution (1001 mb), gets it to as far west as ~90W (when it is near 24.5 N) as of 2 AM ED tonight. So, that will be an interesting benchmark to follow. Then it turns nearly due north and slows down on Friday. It doesn't have it strengthening again to any strong extent until Saurday/Sunday, when it starts moving NNE and then NE. I'm guessing that's because the NNE/NE movement would be more aligned with the upper flow then?

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Thanks! Looks like the models are initialized off the GFS and GEFS grids so its not too surprising to see the intensity guidance so bullish. 

 

 

Yeah I have no idea how well they perform. Just another set of guidance I suppose, but we'll see how they do with this storm.

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There's also a permanent upwelling area with low TCHP just N of the Yucatan which hurts a bit right now-doesn't extend that far north, though.

 

However, there is a very cold eddy that is currently over the C GoM that Karen will be traversing over the next few days. SSTs are in the 28-30C range, the OHC is anomalously low in that same region (lower than the region Ingrid traversed a few weeks ago). 

 

2013275go.jpg

 

2013275gosha.png

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The PSU near real-time system has been run for the past several years and has a pretty good track record.  I haven't monitored the UW-NMS based system for hurricanes, but I know the folks working on it and I'm quite familiar with the model (having gone to school there many years ago), I'll see if I can bug some people for some stats since I have lots of free time right now.

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The GFS Simulated IR temperature (OLR) is a good way to see how Karen is expected to battle the shear on the GFS verbatim. Note how there are repeated  bursts of convection that attempt to axisymmetrize the low-level circulation with the mid-level vortex.

 

http://www.tropicaltidbits.com/analysis/models/gfsfull/2013100312/gfsfull_ir_watl.html

 

This is traditionally how sheared TCs can continue to intensify, in bursts associated with pulses in convection. Each burst of convection produces a convective and stratiform plume that redistributes the PV profile in the mid and upper levels, which attempts to build anticyclonic outflow over the circulation center. The irrotational winds (divergent outflow) aid in temporarily countering the unfavorable synoptic scale flow. In addition, this moistens the core as convective elements rotate cyclonically around the system which allows for subsequent convective bursts that continue this positive feedback. 

 

Sheared storms are so difficult to predict, because its not very well understood whether the synoptic flow or the convective irrotational winds dominate the environment around a TC. In some sheared TC cases, the convection grows upscale and can become a larger contribution to the total flow vs. the non-convective synoptic scale motion. In this case, the synoptic scale flow can be modified enough to go into a new regime that ordinarily wouldn't exist if the TC didn't exist. In other cases, the convective contribution of the storm is not influential enough to modify the synoptic environment of the TC, and the system succumbs to shear. 

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Its rare that WPC embraces the Canadian:

 

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1201 PM EDT THU OCT 03 2013

VALID 12Z SUN OCT 06 2013 - 12Z THU OCT 10 2013


...TROPICAL STORM KAREN WILL IMPACT THE CENTRAL GULF COAST AND SE
STATES...
...THREAT FOR HEAVY RAIN EXPANDING NORTH AND NORTHEAST OF HER
TRACK...

CONFIDENCE IS RELATIVELY HIGH REGARDING THE TRACK OF T.S.
KAREN...WITH A TIGHT ENSEMBLE ENVELOPE AND PRESENCE OF A
DEFINITIVE MID LATITUDE CYCLONE TO SWEEP THE SYSTEM TO THE NNE.
THE MODEL THAT BEST FIT THE OFFICIAL NHC TRACK WHILE ALSO
DEPICTING A WELL DEVELOPED CYCLONE...WAS THE 00Z CANADIAN. THIS
MODEL ALSO DID A REASONABLE JOB WITH THE UPPER MIDWEST
CYCLOGENESIS THROUGH DAY 4. THEREAFTER WE RETURNED TO HEAVIER
RELIANCE ON THE ECMWF ENSEMBLE MEAN...WHEREAS THE OPERATIONAL
ECMWF HAS TENDED TO FALL TOWARD THE SLOWER SIDE OF GUIDANCE. AN
UPSTREAM SHORTWAVE CROSSING THE CANADIAN PRAIRIES SHOULD PHASE
WITH OUR MIDWEST/GREAT LAKES CYCLONE TO YIELD A PHASED LOW LEVEL
CYCLONE LIFTING TOWARD THE SOUTHEASTERN SHORES OF HUDSON BAY BY
DAY 4. THE ATTENDANT COLD FRONT SHOULD MERGE WITH KAREN ON DAY 4
NEAR THE SOUTHERN APPALACHIANS...GENERALLY NEAR THE INTERSECTIONS
OF GA/TN/SC/NC. BEFORE MERGING...MODELS SIGNAL A PREDECESSOR RAIN
EVENT NEAR THE MID MISSISSIPPI VALLEY AND LOWER OHIO VALLEY FROM
DAYS 3 INTO 4. THEREAFTER...THOUGH MIDWEST CYCLONE LIFTS NORTH
QUICKLY...THERE WILL BE A DEFINABLE SHORTWAVE AT THE BASE OF THE
TROUGH APPROACHING THE SOUTHEAST AND MID ATLANTIC STATES.
THIS...IN TANDEM WITH THE NORTHWARD FLUX OF TROPICAL AIR...SHOULD
YIELD A FRONTAL WAVE TO KEEP ORGANIZED HEAVY RAINFALL GOING INTO
AT LEAST DAY 5.

BACK TO THE WEST...WE CONTINUE TO TRUST THE LARGER SCALE
PROGRESSION OF A POSITIVELY TILTED MEAN TROUGH INTO WESTERN NORTH
AMERICA ON DAYS 5-7...WITH THE ECMWF ENSEMBLE MEAN BEING THE
STEADIEST MODELING SYSTEM. THE SHORTWAVE DETAILS SHOW SO MUCH RUN
TO RUN VARIABILITY THAT IT IS DIFFICULT TO SIDE WITH ANY
OPERATIONAL MODEL. BUT SEVERAL RUNS HAVE INDICATED A MORE
PRONOUNCED SHORTWAVE DEVELOPING TOWARD THE BASE OF THE TROUGH
APPROACHING CALIFORNIA AND THE DESERT SOUTHWEST.

BURKE

 

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guys the gfs showed the storm being sheared and convection being displaced to the east of the coc the past 4 runs... it won't ramp up until it nears the coast and beings a ne track.  the thing wasn't ever forecasted to bomb out over the yucatan.  it will be a case of how long the storm has over water as it traverses the coast off miss and the fl panhandle.

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The GFS is the only global model showing this robust solution with a strong TS/hurricane going into the FL panhandle.  All of the other global models are farther to the left and more sheared (although a bit more robust than the last day or two).  Given the current appearance, abundance of shear and dry air in the northern Gulf, it is hard for me to completely buy off on the GFS solution.  As Phil said, it could certainly go through bursts of strengthening as convection periodically builds over the center, but this idea of steady strengthening to the coast and a vertically stacked system turning NE into the FL panhandle...not sure I can see that.

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the main differences in strength in regards to the gfs and the rest of the model guidance (other than the more western tracks into the dry air) is that the gfs gives karen a good 24hrs more over water as it moves ne offshore the gulf coast instead of making landfall before the front can move it ne.  

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