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Potential major phasing event this weekend


forkyfork

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Some early thoughts on Sandy…

The combination of a severe block and deepening trough anchored in the Ohio/Tennessee Valley region that will likely go negative will lead to Sandy’s being captured and reeled to landfall. While the sudden left turn seen repeatedly on the ECMWF would amount to a rare event, it is not unprecedented.

The sharp left turn taken by Tropical Storm Dean (1983) during a strong block, albeit not as strong as the current one, provides an example.

http://weather.unisy.../DEAN/track.gif

Hurricane #8 (1991) aka the “Perfect Storm” provides another illustration. That storm developed during a block that rivals the current one in magnitude.

http://weather.unisy...991/8/track.gif

Right now, my thinking is that the area with the highest possibility of landfall extends from the Virginia Capes to extreme eastern Massachusetts. With Sandy’s being stronger at this stage than had been depicted on some of the guidance from a few days ago and the severe block largely precluding an exit out to sea, I suspect that the deepening trough will have an easier time capturing Sandy. The quickening timeframe for capture may well explain the southward evolution in the guidance over the past 24 hours.

Baroclinic deepening from growing interaction with the trough and Sandy’s passage over the Gulf Stream will likely allow it to conserve much of its strength. Its coming ashore with Category 1 maximum sustained winds is a distinct possibility.

In terms of impacts, even if Sandy comes ashore along the southern region of the Delmarva, its windfield will be expansive. Hence, gales and coastal flooding would be likely along the South Shore of Long Island, the New Jersey Coast, and coastal southern New England. For reference, one should keep in mind that Hurricane #8 (1991) impacted those areas, even as it remained some 150 to 200 miles offshore. Moreover, that storm’s central pressure fell to 972 mb. Sandy might have a central pressure 15-30 mb lower if one errs on the side of conservatism.

Finally, it should be noted that following Hurricane #8 (1991), the Arctic Oscillation rebounded. Some of the ensembles point to a similar outcome following Sandy. Overall, November wound up colder than normal across most of the U.S., except for the West Coast and northern Mid-Atlantic/New England.

The latest run of the CFSv2 shows the eastern third of the U.S. being colder than normal for November, except for northern New England. The major point is that the pattern following Sandy could feature a sizable area of cool anomalies for November. Should that cold materialize, it would remain to be seen whether December would feature the kind of reversal to widespread warmth that occurred in 1991.

Voice of reason...

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Excerpt from the 3:59 AFD from Upton. Bullish wording...

THE MAJORITY OF THE MODELS BRING SANDY OUT TO 70W...EAST OF

HATTERAS...SUNDAY NIGHT BEFORE RECURVING SANDY BACK TOWARDS THE

COAST MONDAY INTO TUESDAY. SOMETIME ON MONDAY...SANDY IS EXPECTED TO

LOSE ITS TROPICAL CHARACTERISTICS...BUT SHOULD STILL BE A

POWERFUL AND HISTORIC STORM SYSTEM FOR THE NORTHEAST. MODELS BEGIN

TO DIVERGE IN SOLUTIONS SUNDAY NIGHT INTO MONDAY MORNING...AS

LANDFALL COULD OCCUR ANYWHERE FROM THE DC METRO AREA TO CAPE COD.

THE OPERATIONAL RUN OF THE 12Z/25 GFS IS THE SLOWEST OF THE

SOLUTIONS...BRINGING SANDY EAST OF 70W ON MONDAY BEFORE TURNING BACK

TOWARDS THE COAST...PASSING EITHER RIGHT OVER OR JUST SOUTH OF LONG

ISLAND AND INTO NYC LATE TUESDAY INTO TUESDAY NIGHT. MOST OF THE GFS

ENSEMBLE MEMBERS FOLLOW A SIMILAR TRACK...THOUGH ARE ABOUT 6-12

HOURS FASTER THAN THE OPERATIONAL RUN. SEVERAL OF THE MEMBERS CARRY

SANDY OUT TO SEA...BUT THAT IS AN OUTLIER.

THE 12Z/25 CMC MODEL IS JUST TO THE WEST OF THE GFS...AND IS ABOUT

6-12 HOURS FASTER. THIS BRINGS THE LOW JUST SOUTH OF LONG ISLAND

MONDAY AFTERNOON...THEN OVER NYC MONDAY EVENING BEFORE TRACKING BACK

TOWARDS WESTERN NY/PA.

THE 12Z/25 ECMWF CONTINUES ITS WESTERN TRACK...BARELY MAKING IT TO

70W ON SUNDAY BEFORE SHARPLY TURNING BACK TOWARDS THE COAST ON

MONDAY...MAKING LANDFALL JUST OVER WALLOPS ISLAND...VA BY TUESDAY

MORNING. THIS COULD POSE A PARTICULARLY DANGEROUS SCENARIO...AS

STRONG SOUTHERLY WINDS OFF THE OCEAN WOULD BATTER COASTAL AREAS.

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That map is a guide for absolute maximum strength from barotropic forces. Even if Sandy is a warm occlusion cyclone by the time it get north of 35N, it will be deriving much of its strength from baroclinic forcing. It's pretty much a foregone conclusion that Sandy/post-Sandy will be deeper than 990-1000mb when it gets up here.

Of course; what this shows is how much Sandy can intensify to in the next 24-48 hours.

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Euro ensembles are further north than the OP.

http://raleighwx.ame...mbTSLPUS168.gif

That's generally a track that seems the most reasonable to me. Sandy would have to be captured very early and recurve quite soon to allow a landfall as far south as the Euro, but perhaps the strength of the block would allow such a fast capture. GFS and GGEM certainly seem to be trending in its direction. However, it's such a fragile situation that almost anyone is still in the game along the Mid-Atlantic and Northeast coasts. Scary as it gets here.

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Hurricane SANDY Forecast Discussion

Home Public Adv Fcst Adv Discussion Wind Probs Graphics Archive

US Watch/Warning

000

WTNT43 KNHC 252037

TCDAT3

HURRICANE SANDY DISCUSSION NUMBER 14

NWS NATIONAL HURRICANE CENTER MIAMI FL AL182012

500 PM EDT THU OCT 25 2012

SATELLITE IMAGERY SHOWS THAT STRUCTURAL CHANGES ARE ALREADY

OCCURRING WITH SANDY. DRY AIR ALOFT AND SOUTHWESTERLY FLOW

ASSOCIATED WITH AN UPPER-LEVEL LOW CENTERED NEAR WESTERN CUBA ARE

IMPINGING ON THE WEST SIDE OF THE CIRCULATION. AS A RESULT...THE

OUTFLOW IS RESTRICTED IN THE SOUTHWEST QUADRANT AND THE CLOUD

PATTERN IS BECOMING MORE ASYMMETRIC. HOWEVER...THE HIGHEST FLIGHT-

LEVEL WINDS FROM THE AIRCRAFT WERE STILL 109 KT AT THE END OF THE

LAST MISSION AND THE CENTRAL PRESSURE REMAINS AT 963 MB. THE

INITIAL INTENSITY REMAINS 90 KT FOR THIS ADVISORY. SOME DECREASE IN

THE MAXIMUM WINDS IS EXPECTED DURING THE NEXT COUPLE OF DAYS AS

SANDY BECOMES MORE ENTANGLED WITH THE UPPER-LEVEL LOW...HOWEVER THE

GLOBAL MODELS SHOW SANDY REMAINING A VERY DEEP CYCLONE AND THE WIND

FIELD EXPANDING DURING THIS TIME. LATER IN THE PERIOD...SOME

RE-INTENSIFICATION IS SHOWN AS SANDY DEEPENS AGAIN OFF THE U.S.

EAST COAST WHILE IT INTERACTS WITH ANOTHER SHORTWAVE TROUGH.

REGARDLESS...SANDY IS EXPECTED TO BE A LARGE CYCLONE AT OR NEAR

HURRICANE INTENSITY THROUGH MOST OF THE FORECAST PERIOD.

THE INITIAL MOTION ESTIMATE IS 360/17...AS SANDY HAS BEGUN TO

ACCELERATE NORTHWARD DUE TO THE UPPER LOW. THE REASONING FOR THE

TRACK FORECAST REMAINS LARGELY UNCHANGED. SANDY WILL BE PULLED

NORTHWESTWARD AND SLOW DOWN ON FRIDAY WHILE IT INTERACTS WITH THE

UPPER-LEVEL LOW. THEN A NORTH-NORTHEASTWARD ACCELERATION IS

EXPECTED BY SATURDAY AS A LONGWAVE TROUGH MOVES INTO THE EASTERN

UNITED STATES. MOST OF THE TRACK MODELS NOW SHOW A TURN BACK TOWARD

THE NORTHWEST BY THE END OF THE PERIOD DUE TO SANDY INTERACTING

WITH AN AMPLIFYING SHORTWAVE TROUGH OVER THE CAROLINAS AND

MID-ATLANTIC STATES. HOWEVER...THERE REMAIN SOME SIGNIFICANT

DIFFERENCES IN THE TIMING OF THIS INTERACTION...AS THE ECMWF HAS

SANDY FARTHER WEST AND INTERACTING WITH THE SHORTWAVE SOONER

RELATIVE TO MOST OF THE REST OF THE GUIDANCE...WHICH SHOWS A WIDER

TURN AND A TRACK FARTHER NORTH. THE NEW NHC FORECAST IS CLOSE TO

THE PREVIOUS ONE...AND LIES ROUGHLY BETWEEN THE ECMWF AND THE GFS

ENSEMBLE MEAN. REGARDLESS OF THE EXACT TRACK OF SANDY...IT IS

LIKELY THAT SIGNIFICANT IMPACTS WILL BE FELT OVER PORTIONS OF THE

U.S. EAST COAST THROUGH THE WEEKEND AND INTO EARLY NEXT WEEK.

NOTE THAT THE TROPICAL CYCLONE WIND SPEED PROBABILITIES ARE NOT

DESIGNED TO HANDLE THE TYPE OF STRUCTURAL CHANGES ANTICIPATED WITH

SANDY DURING THE FORECAST PERIOD. AS A RESULT...THESE PROBABILITIES

WILL UNDERESTIMATE THE ACTUAL RISK OF STRONG WINDS AWAY FROM THE

CENTER OF SANDY.

FORECAST POSITIONS AND MAX WINDS

INIT 25/2100Z 24.5N 75.6W 90 KT 105 MPH

12H 26/0600Z 26.0N 76.0W 85 KT 100 MPH

24H 26/1800Z 27.4N 77.0W 80 KT 90 MPH

36H 27/0600Z 28.3N 77.0W 75 KT 85 MPH

48H 27/1800Z 29.8N 76.0W 65 KT 75 MPH

72H 28/1800Z 33.0N 73.0W 70 KT 80 MPH

96H 29/1800Z 37.5N 72.5W 70 KT 80 MPH

120H 30/1800Z 40.5N 75.0W 55 KT 65 MPH...POST-TROPICAL

$$

FORECASTER BRENNAN

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Sandy does not look healthy at all right now...

SOME DECREASE IN

THE MAXIMUM WINDS IS EXPECTED DURING THE NEXT COUPLE OF DAYS AS

SANDY BECOMES MORE ENTANGLED WITH THE UPPER-LEVEL LOW...HOWEVER THE

GLOBAL MODELS SHOW SANDY REMAINING A VERY DEEP CYCLONE AND THE WIND

FIELD EXPANDING DURING THIS TIME. LATER IN THE PERIOD...SOME

RE-INTENSIFICATION IS SHOWN AS SANDY DEEPENS AGAIN OFF THE U.S.

EAST COAST WHILE IT INTERACTS WITH ANOTHER SHORTWAVE TROUGH.

REGARDLESS...SANDY IS EXPECTED TO BE A LARGE CYCLONE AT OR NEAR

HURRICANE INTENSITY THROUGH MOST OF THE FORECAST PERIOD.

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