East Coast High Impact Hurricane/Post Tropical Storm Sandy

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PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER COLLEGE PARK MD
436 AM EDT FRI OCT 26 2012

VALID 12Z TUE OCT 30 2012 - 12Z FRI NOV 02 2012

...HURRICANE/POST-TROPICAL CYCLONE SANDY IS LIKELY TO SPREAD HIGH
WINDS/HEAVY RAINS/HEAVY MOUNTAIN SNOWS FROM THE CAROLINAS AND
CENTRAL APPALACHIANS NORTHWARD INTO CANADA...


GENERAL FLOW PATTERN
====================
A RETROGRADING POSITIVE ANOMALY MOVING FROM SOUTHERN GREENLAND
INTO NORTHERN QUEBEC FAVORS A QUASI-STATIONARY DEEP CYCLONE NEAR
THE NORTHEAST, IN THIS CASE HURRICANE SANDY AND ITS POST-TROPICAL
REMAINS. OTHERWISE...RIDGING IS GENERAL EXPECTED OUT
WEST...THOUGH QUASI-ZONAL FLOW ACROSS THE PACIFIC IS EXPECTED TO
SEND ENERGY ACROSS THE NORTHWEST. THE GUIDANCE IS IN EXCELLENT
AGREEMENT ON THE GENERAL FLOW PATTERN, THOUGH LARGE DETAIL ISSUES
REMAIN WITH SANDY'S FUTURE COURSE AND STRENGTH, KEEPING CERTAINTY
IN THE PATTERN ACROSS THE NORTHEAST BELOW AVERAGE.

MODEL PREFERENCE
================
THE NATIONAL HURRICANE CENTER (NHC) TRACK BEST RESEMBLES A
40/20/20/20 BLEND OF THE 12Z ECMWF ENSEMBLE MEAN/00Z ECMWF/00Z
GFS/00Z UKMET, WHICH WAS USED FOR MONDAY THROUGH WEDNESDAY. FOR
THURSDAY AND NEXT FRIDAY, TRANSITIONED TO A 00Z GFS/00Z ECMWF
COMPROMISE AS THEIR SOLUTIONS WITH SANDY CONVERGE. THE
EXTRATROPICAL TRANSITION OF SANDY MAY HAVE ALREADY BEGUN BASED
UPON RECENT SATELLITE IMAGERY...A PROCESS EXPECTED TO COMPLETE
BETWEEN TUESDAY AND WEDNESDAY PER NHC. THE DETERMINISTIC GUIDANCE
(PARTICULARLY THE 00Z ECMWF) SHOW PRESSURE SOLUTIONS WELL BEYOND
WHAT HAS EVER BEEN OBSERVED NEAR THE NEW JERSEY/NEW YORK COAST
(EVEN EXCEEDING THE 1938 LONG ISLAND EXPRESS HURRICANE) EARLY IN
THE MEDIUM RANGE PERIOD. THE DETERMINISTIC GUIDANCE (CANADIAN,
GFS, AND ECMWF INCLUDED) HAS SHOWN A VERY STRONG BIAS WITH
TROPICAL CYCLONES GAINING LATITUDE AND/OR TRANSITIONING INTO
NON-TROPICAL STORMS OVER THE PAST COUPLE YEARS, INCLUDING (BUT NOT
EXCLUSIVE TO) LESLIE 2012, ISAAC 2012, DEBBY 2012 IN THE WESTERN
SUBTROPICAL ATLANTIC, IRENE 2011, AND IGOR 2010. EVEN THE
PERFECT/HALLOWEEN STORM OF 1991 "ONLY" BOTTOMED OUT AT 972 HPA,
AND THIS FORECAST WAS ALLOWED TO EXCEED THAT SYSTEM WITHOUT GOING
OVERBOARD. PRESSURES FOR THE STORM WERE CAPPED AROUND 965 HPA
EARLY IN THE PERIOD PRIOR TO LANDFALL, AND ALLOWED TO WEAKEN ONCE
INLAND. THIS WAS COORDINATED WITH THE OCEAN PREDICTION CENTER
(OPC) AND IS CLOSE TO THE PAST COUPLE DAYS OF HPC/OPC CONTINUITY.
KEEP IN MIND THIS PREFERENCE WOULD INDICATE THAT THE MODEL-DERIVED
QPFS FOR THE GUIDANCE SHOWING CENTRAL PRESSURES UNDER 965 HPA ARE
LIKELY TOO EXCESSIVE DUE TO THEIR EXTREME LOW PRESSURE SOLUTIONS
FOR SANDY.


WEATHER IMPACTS
===============
PER THIS SOLUTION, FROM SUNDAY THROUGH WEDNESDAY, WINDS NEAR
HURRICANE-FORCE ARE EXPECTED TO LASH EXPOSED AREAS OF THE
NORTHEAST/MID-ATLANTIC STATES (THE COAST AND TOPOGRAPHY), LEADING
TO POTENTIALLY SERIOUS COASTAL EROSION AND COASTAL FLOODING. THE
TIMING OF THE FULL MOON AND THE BUILD-UP OF TIDES OVER MULTIPLE
TIDAL CYCLES SHOULD EXACERBATE THE SITUATION ALONG THE COAST,
PARTICULARLY IN CORNERS SUCH AS THE NEW YORK BIGHT. HEAVY RAINS
ARE EXPECTED TO FOCUS WITHIN SANDY'S WARM CONVEYOR BELT
CIRCULATION AS WELL AS ALONG ITS DRAPING WARM FRONT FROM THE
NORTHERN MID-ATLANTIC STATES INTO EASTERN CANADA, WITH LOCAL
AMOUNTS EXCEEDING 10 INCHES POSSIBLE. THIS SOLUTION WOULD ALLOW
SIGNIFICANT SNOWS WITHIN ITS COMMA HEAD PATTERN TO FALL ACROSS THE
MOUNTAINS OF WEST VIRGINIA/WESTERN PENNSYLVANIA/EASTERN OHIO;
LIKELY NOT TO THE EXTREME DEGREE SEEN WITHIN ANY OF THE CURRENT
DETERMINISTIC GUIDANCE. LAKE EFFECT SNOWS ACROSS THE EASTERN
GREAT LAKES ARE POSSIBLE THROUGH THE PERIOD WITHIN THE CYCLONIC
FLOW IN THE SYSTEM'S COLD SECTOR.
AS THE CYCLONE WEAKENS AS IT
PULLS NORTHWARD THURSDAY INTO NEXT FRIDAY, WINDS SHOULD SLACKEN AS
SHOULD PRECIPITATION AMOUNTS/COVERAGE ACROSS THE NORTHEAST.

ROTH
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HPC 5 Day QPF Forecast:
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10262012 1139Z Sandy latest.jpg
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Email from Jeff (and one of the most "eye opening" emails too).
Potentially historic and unprecedented hurricane potential for the NE US coast.

Over the next 5 days a set of extraordinary meteorological factors will come together to potentially produce a hurricane impact on the NE US coast that has never before been experienced since the founding of this nation and the keeping of written weather records.

In response to this potential threat, all US weather balloon sounding stations are launching upper air balloons every 6 hours to incorporate the latest data into the forecast models in support of NHC and HPC forecasting operations…this has never happened before!

The following discussion will attempt to explain this complex set of parameters for what appears to be an increasing likely extremely high impact but never before seen event!

Background:
Hurricanes striking the NE US are not overly uncommon…just last year Irene moved into the same area causing extensive damage and the area which has one of the longest periods of recorded weather history anywhere in the US has been hit several times before by hurricanes. To understand what is forecasted to take place this weekend and early next week, one must look at the fundamental differences between what is called a tropical cyclone…hurricane and what is called post tropical (extra-tropical). To simplify, a tropical cyclone is warm core with no surface temperature gradients (same air mass before and after passage) and they gain intensity from warm waters below. Post tropical (extra-tropical) as usually system higher in latitude than tropical cyclones that do have temperature gradients (cold and warm fronts) and gain intensity not so much from warm water, but the differences in those temperature gradients and jet stream dynamics aloft. Many times as tropical cyclones move out of the tropics and northward into the higher latitude they encounter increasingly colder air masses that wrap into the system and the transition begins from tropical (warm core) to post tropical or cold core (with fronts). An example of a type of extra-tropical system would be a nor’easter.

Upper Air Pattern for this Event:
The upper air pattern over North America and over the North Atlantic is becoming increasingly blocked…weather systems such as big high and low pressure centers are slowing down and will become nearly stationary. Massive high pressure is building over Greenland currently while a large longwave trough is developing over the central and eastern US. Due to the high latitude blocking that is going into place these large scale features will remain nearly stationary in place for the next 5-7 days.

The longwave trough currently developing over the eastern US will become increasingly negative titled (oriented NW to SE instead of SW to NE). Most of the time troughs nearing the east coast are positive tilted (SW to NE) and hurricanes to their SE (where Sandy currently is) are steered N and NE out to sea. In fact all hurricanes that have affected the NE US since 1851 have had tracks from the SW to the NE consistent with a SW to SE steering flow. The difference with this event is the downstream blocking high over Greenland which will prevent Sandy from accelerating NE into the Atlantic and also a strong shortwave trough which moves through the large longwave trough and helps to capture Sandy into the trough.

With the trough anchored over the SE US and mid Atlantic producing an increasingly strong SE steering flow and blocking high pressure over Greenland, Sandy has little choice but to turn back toward the NW or even WNW and strike the US coast. A hurricane has never struck the US mid Atlantic or NE coast moving toward the NW or WNW or at a right angle to the coast as Sandy is forecast to do. Historical storms generally move SW to NE parallel to the coast with the greatest impacts offshore or over extreme east MA and Cape Cod.

As far as the models predicted track go, they are doing a good job with a rare pattern with only modest amounts of spread. Generally the ECMWF continues to be on the west and southern edge of the guidance taking Sandy into the southern DELMARVA area while the GFS and CMC are further north into Long Island (NYC) and southern New England. The current NHC forecast track is splitting the difference with slightly more weight toward the ECMWF which was the first model to predict this “highly anomalous event” and has remained very consistent over the past 2-3 days.

Model Intensification (Tropical vs. Post Tropical):
For reference the powerful 1938 Long Island hurricane holds most of the low pressure records over the NE US. A central pressure of 946mb was recorded as this storm moved inland over southern Long Island producing the highest storm surge on record on Long Island and into southern New England. The 1991 “Perfect Storm” had a central pressure of around 972mb which produced significant coastal damage from North Carolina to Maine. I list these benchmark events as comparisons to what the models are showing for Sandy.

Every forecast model except the NAM is forecasting a sub 960mb storm which would be significantly lower than the 1991 event. However most of the model guidance is producing a sub 940mb storm which has never occurred over the NE US before (946mb is the lowest recorded pressure). To understand what this means, the lower the pressure the stronger the storm system…in the tropics such pressures as this would equal to a category 4-5 hurricane. However, it will not be that simple! Sandy is already starting to undergo changes in her internal structure this morning with the inner core winds weakening and the wind field expanding outward a feature closer to a post tropical system (large weaker wind field) than a tropical system (smaller more concentrated wind field). Even if these super low pressure are to verify, the system would not produce category 4-5 winds as the pressure gradient would be spread out of hundreds of miles with a massive area of 70-90mph winds.

The question is why are the forecast models predicting such “historic” low pressures with this event and are they correct?

1) One would expect a true hurricane (tropical cyclone) to weaken as it moves northward into a colder and drier air mass over the NE US and adjacent Atlantic waters. Additionally water temperatures along the track are generally below the threshold needed for tropical cyclone intensification.
2) If the real world data does not support tropical cyclone intensification, then why are the models all showing it? The system is expected to gain more and more extra-tropical features as it moves northward which means it starts to draw its energy sources from temperature gradients and jet stream dynamics instead of the warmer waters. What is likely happening in the models is that the warm and moist influx of Caribbean air with Sandy will greatly intensify the temperature gradient with the SE moving polar air mass from Canada and help intensity the overall storm. Additionally, Sandy’s surface low will be in a favorable region of the trough to provide strong upper level divergence aloft which will help promote intensification.
3) However…what is interesting is that many of the models keep Sandy warm core or tropical toward landfall while intensifying in conditions that would be marginal at best for a tropical cyclone to hold its intensity. It is likely that Sandy will be something of an “in between system” drawing energy initially from the warm Gulf stream below and then more and more from the mid latitude jet and temperature influences.
4) The models could be completely wrong on the pressures (it would not be the first time). However, it must be noted that nearly every model is showing the same very low pressure and that does add credibility to their solutions.

Possible Impacts:
As with any rare weather event the impacts are somewhat of an unknown. Additionally the uncertainty of how Sandy will evolve and how is curves back toward the US coast will drive where and how severe the impacts will be.

It can be easily stated that should the forecast track and models “spectacular” low pressure verify a storm of rare intensity and tremendous impacts will be felt along the NE and mid-Atlantic coast. Given the forecasted perpendicular strike on the coast, onshore winds will push the Atlantic Ocean inland along the New Jersey and New York coast including New York City. Due to the high blocking over Greenland, the fetch of wind will extend nearly across the entire Atlantic Ocean and this will result in massive wave action aimed at the NE US coast. Lunar tides are also near peak with the full moon on Monday and this combined with the wave run-up and long duration of onshore winds (20-30 hours at 60-80mph) will result in potentially record breaking storm surge values. The potential is there for coastal inundation of sea water never before experienced in the NE US including New York City, but this depends heavily on the exact track of the center of Sandy.

Strong winds will batter much of the mid Atlantic and NE for not hours but days as Sandy moves NW to WNW and slows. These winds will last anywhere from 20-30 hours at 60-80mph with higher gust resulting in widespread power outages and downed trees. Strong winds will spread well inland from the coast into Canada and the OH valley.

Rainfall will be extensive as tropical moisture is brought northward with Sandy and pushed against a stalled front nearly along the higher terrain of the Appalachian mountains. Flooding rainfall due to the high rainfall rates and slow storm motion is likely and it is possible some rivers will reach record crests.

Impacts over the open Atlantic will be severe with a massive area of sustained winds of 60-70mph over hundreds of miles. Wave heights will build into the 20-30 foot range and I would not be surprised to see heights build toward 40-45 feet. Visibilities will be reduced to near zero in blowing sea spray and heavy rainfall.

Potential for widespread travel and commerce disruption as air, surface, sea, and rail travel will likely be significantly impacted along with widespread long term power outages which could last well into November.
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I'm surprised there's not more discussion about this. Sandy looks like one crazy beast.
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michmich wrote:I'm surprised there's not more discussion about this. Sandy looks like one crazy beast.

Actually I believe there will be in the days and hours to come. What we are potentially looking at is a once in a lifetime type weather event that will impact multi millions of folks. From the pure science of weather as the professional and enthusiast alike, the societal impact of this potential threat have not been experienced before and that alone will drive the interest level as we head toward early next week.
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HURRICANE SANDY DISCUSSION NUMBER 17
NWS NATIONAL HURRICANE CENTER MIAMI FL AL182012
1100 AM EDT FRI OCT 26 2012

STRONG SOUTH-SOUTHWESTERLY SHEAR AND THE INTRUSION OF DRY AIR
CONTINUES TO AFFECT THE HURRICANE...AS VISIBLE SATELLITE IMAGES
SHOW THAT THE LOW-LEVEL CENTER OF SANDY IS EXPOSED TO THE SOUTH OF
THE MAIN MASS OF CONVECTION. USING A BLEND OF FLIGHT-LEVEL AND
SFMR WINDS FROM THE HURRICANE HUNTER AIRCRAFT YIELDS A CURRENT
INTENSITY ESTIMATE OF 70 KT. DYNAMICAL MODELS SHOW AN ADDITIONAL
INCREASE IN SHEAR OVER THE NEXT 24 HOURS...WHICH SHOULD CAUSE AT
LEAST SLIGHT WEAKENING. LATER IN THE FORECAST PERIOD...GLOBAL
MODELS SHOW SOME RE-INTENSIFICATION OF THE CYCLONE...WHICH IS VERY
LIKELY DUE TO BAROCLINIC INFLUENCES. BY 72 HOURS...THE MODELS SHOW
SIGNIFICANT COLD AIR ADVECTION OVER THE SOUTHWEST PORTION OF THE
CIRCULATION...WHICH SHOULD HASTEN THE EXTRATROPICAL TRANSITION
PROCESS. THE OFFICIAL FORECAST SHOWS THE SYSTEM AS POST-TROPICAL
AT 96 HOURS...THOUGH THERE IS SOME UNCERTAINTY AS TO THE TIMING OF
THE TRANSITION. REGARDLESS...WHETHER SANDY IS OFFICIALLY TROPICAL
OR POST-TROPICAL AT LANDFALL WILL HAVE LITTLE BEARING ON THE
IMPACTS.


LATEST FIXES FROM HURRICANE HUNTER AIRCRAFT SHOW A VERY SLOW MOTION
WITH THE CENTER APPEARING TO HAVE TURNED NORTHWARD. THE CURRENT
MOTION ESTIMATE IS 360/5. SANDY IS EXPECTED TO ESCAPE THE
INFLUENCE OF A MID- TO UPPER-LEVEL TROUGH AND TO BEGIN TO MOVE
NORTH-NORTHEASTWARD TO NORTHEASTWARD WITH AN INCREASE IN FORWARD
SPEED OVER THE NEXT FEW DAYS. A SHORTWAVE TROUGH NEAR THE PACIFIC
NORTHWEST COAST IS FORECAST TO MOVE EAST-SOUTHEASTWARD AND DIG AS
IT APPROACHES THE EASTERN U.S. COAST BY 72 HOURS. THE FLOW ON THE
NORTHEAST SIDE OF THIS SHORTWAVE SHOULD CAUSE SANDY TO TURN TOWARD
THE NORTH AND NORTHWEST TOWARD THE COAST. THE OFFICIAL TRACK
FORECAST IS VERY SIMILAR TO THE PREVIOUS ONE AND ALSO VERY CLOSE TO
THE LATEST DYNAMICAL MODEL CONSENSUS. USERS ARE REMINDED TO NOT
FOCUS ON THE DETAILS OF THE TRACK FORECAST LATE IN THE PERIOD...AS
SANDY IS EXPECTED TO BRING IMPACTS TO A LARGE PART OF THE U.S. EAST
COAST INTO EARLY NEXT WEEK.


FORECAST POSITIONS AND MAX WINDS

INIT 26/1500Z 26.7N 76.9W 70 KT 80 MPH
12H 27/0000Z 27.6N 77.4W 70 KT 80 MPH
24H 27/1200Z 28.9N 76.8W 65 KT 75 MPH
36H 28/0000Z 30.5N 75.5W 65 KT 75 MPH
48H 28/1200Z 32.2N 73.7W 70 KT 80 MPH
72H 29/1200Z 36.0N 72.5W 70 KT 80 MPH
96H 30/1200Z 39.0N 75.5W 65 KT 75 MPH...POST-TROPICAL
120H 31/1200Z 40.5N 78.0W 50 KT 60 MPH...POST-TROP/EXTRATROP

$$
FORECASTER PASCH
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Karen
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Couple of questions.
1. what changed the original track had the storm going to sea a couple of days ago
2. is there anything that will change the direction and possibly push this back to sea
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Karen wrote:Couple of questions.
1. what changed the original track had the storm going to sea a couple of days ago
2. is there anything that will change the direction and possibly push this back to sea

There is a large blocking High Pressure to the N. The GFS was really the only model that has suggested an out to sea motion earlier, but that has changed.
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good sat shot from our friends to the north, open the link for best view

http://www.weatheroffice.gc.ca/data/sat ... vi_100.jpg

Image
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12 GFS:
10262012 12Z GFS USA_PRMSL_msl_096.gif
12Z Euro:
10262012 12Z Euro USA_PRMSLI_msl_096.gif
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EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER COLLEGE PARK MD
226 PM EDT FRI OCT 26 2012

VALID 12Z MON OCT 29 2012 - 12Z FRI NOV 02 2012

...DANGEROUS HURRICANE/POST-TROPICAL CYCLONE SANDY IS LIKELY TO
SPREAD HIGH WINDS/HEAVY RAINS AND INTERIOR HEAVY SNOWS FROM THE
CAROLINAS AND CENTRAL APPALACHIANS NORTHWARD INTO CANADA...


GENERAL FLOW PATTERN
====================
A RETROGRADING POSITIVE ANOMALY MOVING FROM SOUTHERN GREENLAND
INTO NORTHERN QUEBEC FAVORS A QUASI-STATIONARY DEEP CYCLONE NEAR
THE NORTHEAST, IN THIS CASE HURRICANE SANDY AND ITS POST-TROPICAL
REMAINS. OTHERWISE...RIDGING IS GENERAL EXPECTED OUT
WEST...THOUGH FLOW ACROSS THE PACIFIC IS EXPECTED TO SEND AMPLE
ENERGY/HEAVY PRECIPITATION ACROSS THE NORTHWEST. GUIDANCE IS IN
EXCELLENT AGREEMENT ON THE GENERAL FLOW PATTERN, THOUGH ISSUES
REMAIN WITH SANDY'S FUTURE COURSE AND STRENGTH.

MODEL PREFERENCE
================
THE NATIONAL HURRICANE CENTER (NHC) TRACK NOW BEST RESEMBLES THE
00 UTC ECMWF ENSEMBLE MEAN. THE EXTRATROPICAL TRANSITION OF SANDY
MAY HAVE ALREADY BEGUN BASED UPON RECENT SATELLITE IMAGERY...A
PROCESS EXPECTED TO COMPLETE TUESDAY PER NHC. THE DETERMINISTIC
GUIDANCE (PARTICULARLY THE 00 UTC ECMWF) SHOW PRESSURE SOLUTIONS
WELL BEYOND WHAT HAS EVER BEEN OBSERVED NEAR THE NEW JERSEY/NEW
YORK COAST (EVEN EXCEEDING THE 1938 LONG ISLAND EXPRESS HURRICANE)
EARLY IN THE MEDIUM RANGE PERIOD. THE DETERMINISTIC GUIDANCE
(CANADIAN, GFS, AND ECMWF INCLUDED) HAS SHOWN A VERY STRONG BIAS
WITH TROPICAL CYCLONES GAINING LATITUDE AND/OR TRANSITIONING INTO
NON-TROPICAL STORMS OVER THE PAST COUPLE YEARS... INCLUDING (BUT
NOT EXCLUSIVE TO) LESLIE 2012...ISAAC 2012...DEBBY 2012 IN THE
WESTERN SUBTROPICAL ATLANTIC IRENE 2011 AND IGOR 2010. PLEASE
REFER TO THE NHC FOR UPDATED INFORMATION ON SANDY.

THE 00 UTC ECMWF ENSEMBLE MEAN ALSO DEPICTS AN OVERALL FLOW
PATTERN UPSTREAM ACROSS THE W-CENTRAL CONUS AND ERN PACIFIC THAT
IS ON THE MORE AMPLIFIED AND LESS PROGRESSIVE SIDE OF THE FULL
ENVELOPE OF GUIDANCE SOLUTIONS OVER THE NEXT WEEK. THIS SEEMS
QUITE REASONABLE CONSIDERING DOWNSTREAM BLOCKING.

WEATHER IMPACTS
===============
PER THIS SOLUTION FROM SUNDAY THROUGH WEDNESDAY...WINDS AS HIGH AS
HURRICANE-FORCE ARE EXPECTED TO LASH EXPOSED AREAS OF THE
NORTHEAST/MID-ATLANTIC STATES (THE COAST AND TOPOGRAPHY)...LEADING
TO POTENTIALLY SERIOUS COASTAL EROSION AND COASTAL FLOODING. THE
TIMING OF THE FULL MOON AND THE BUILD-UP OF TIDES OVER MULTIPLE
TIDAL CYCLES SHOULD EXACERBATE THE SITUATION ALONG THE
COAST...PARTICULARLY IN CORNERS SUCH AS THE NEW YORK BIGHT. HEAVY
RAINS ARE EXPECTED TO FOCUS WITHIN SANDY'S WARM CONVEYOR BELT
CIRCULATION AS WELL AS ALONG ITS DRAPING WARM FRONT FROM THE
NORTHERN MID-ATLANTIC STATES AND INTO NEW ENG AND ERN
CANADA...WITH LOCAL AMOUNTS EXCEEDING 10 INCHES POSSIBLE.
THIS
SOLUTION WOULD MEANWHILE ALLOW SIGNIFICANT SNOWS WITHIN ITS COMMA
HEAD PATTERN UNDER THE SUPPORTING/COOLING MID-UPPER LEVEL TROUGH
TO FALL AS CENTERED/FOCUSING OVER THE CENTRAL THEN NRN
APPALACHIANS AND VICINITY. LAKE EFFECT SNOWS ACROSS THE EASTERN
GREAT LAKES ARE POSSIBLE THROUGH THE PERIOD WITHIN THE CYCLONIC
FLOW IN THE SYSTEM'S COLD SECTOR.
AS THE CYCLONE GRADUALLY WEAKENS
AS IT PULLS NORTHWARD THURSDAY INTO NEXT FRIDAY...WINDS SHOULD
SLACKEN AS SHOULD NERN US PRECIPITATION AMOUNTS/COVERAGE...BUT
EXPECT THAT AMOUNTS WILL REMAIN SIGNIFICANT CONSIDERING TROPICAL
ORIGIN OF THE LOW.


UPSTREAM...A SOLUTION CLOSEST TO THE 00 UTC ECMWF ENSEMBLE MEAN
SLOWS FROM HPC CONTINUITY SLIGHTLY THE INLAND PROGRESSION OF ERN
PACIFIC SYSTEM ENERGY ACROSS THE WRN US MID-LATE NEXT WEEK...MORE
SLUGGISH TO BUMP INTO A LEAD AMBIENT MEAN MID-UPPER RIDGE
POSITION. THIS SOLUTION OFFERS STRONG POTENTIAL FOR HEAVY
PRECIPIATION/MOUNTAIN SNOWS ACROSS MUCH OF THE NWRN US NEXT
WEEK...INCLUDING THE THREAT FOR MEDIUM RANGE DAYS 4-7 LIQUID
AMOUNTS UPWARDS TO 5 INCHES OVER MOST FAVORED PAC NW COASTAL
TERRAIN AND THE CASCADES...WITH DECREASING BUT STILL WIDESPREAD
AMOUNTS SPREADING FURTHER INLAND.

ROTH/SCHICHTEL
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10262012_1915_goes13_x_vis2km_18LSANDY_65kts-971mb-270N-771W_100pc.jpg
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18Z Tracks & Intensity:
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10262012 18Z Sandy aal18_2012102618_track_early.png
10262012 18Z Sandy aal18_2012102618_intensity_early.png
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HURRICANE SANDY DISCUSSION NUMBER 18
NWS NATIONAL HURRICANE CENTER MIAMI FL AL182012
500 PM EDT FRI OCT 26 2012

THE LOW-LEVEL CENTER OF SANDY REMAINS EXPOSED TO THE SOUTH OF THE
MAIN AREA OF DEEP CONVECTION AS STRONG SHEAR CONTINUES TO INFLUENCE
THE SYSTEM. THE LAST RECONNAISSANCE MISSION INTO THE TROPICAL
CYCLONE SUGGESTED THAT THE INTENSITY MAY BE DROPPING BELOW
HURRICANE STATUS. THE CURRENT WIND SPEED IS HELD AT 65 KT PENDING
THE NEXT AIR FORCE HURRICANE HUNTER MISSION SCHEDULED FOR A 0000
UTC CENTER FIX. THE SHIPS OUTPUT INDICATES THAT THE SHEAR WILL
REMAIN QUITE STRONG FOR THE NEXT DAY OR SO...AND THEREFORE THE NHC
FORECAST INDICATES WEAKENING FOR THE NEXT 36 HOURS OR SO.
THEREAFTER...THE GLOBAL MODELS SHOW DEEPENING OF THE CYCLONE
PRESUMABLE DUE TO BAROCLINIC FORCING. THIS IS ALSO INDICATED IN
THE OFFICIAL INTENSITY FOREACST. THE GLOBAL MODELS ALSO SUGGEST
THAT SANDY COULD TRANSITION INTO A FULLY EXTRATROPICAL CYCLONE IN 3
TO 4 DAYS.

THE MOTION CONTINUES TO BE RATHER SLOW AND...IN FACT...RECENT
VISIBLE IMAGES SUGGEST LITTLE SHORT-TERM MOVEMENT OF THE CENTER.
HOWEVER A MORE REPRESENTATIVE ESTIMATE OF THE MOTION IS NEAR 360/6.
AFTER SANDY ESCAPES THE INFLUENCE OF A MID- TO UPPER-LEVEL LOW TO
ITS WEST...THE CYCLONE SHOULD MOVE NORTH-NORTHEASTWARD TO
NORTHEASTWARD WITH SOME INCREASE IN FORWARD SPEED. BY AROUND 72
HOURS...A NEGATIVELY-TILTED SHORTWAVE TROUGH NEAR THE U.S. EAST
COAST AND A RIDGE OVER EXTREME EASTERN CANADA SHOULD CAUSE SANDY TO
TURN TOWARD THE NORTHWEST AND WEST-NORTHWEST TOWARD AND OVER THE
U.S. COAST. INTERESTS ARE REMINDED NOT TO FOCUS ON THE EXACT TRACK
OF THIS SYSTEM SINCE SIGNIFICANT IMPACTS WILL EXTEND WELL AWAY FROM
THE LOCATION OF THE CENTER.

FORECAST POSITIONS AND MAX WINDS

INIT 26/2100Z 27.3N 77.1W 65 KT 75 MPH
12H 27/0600Z 28.3N 77.0W 60 KT 70 MPH
24H 27/1800Z 29.7N 76.1W 55 KT 65 MPH
36H 28/0600Z 31.3N 74.3W 55 KT 65 MPH
48H 28/1800Z 33.1N 72.6W 65 KT 75 MPH
72H 29/1800Z 37.0N 71.5W 70 KT 80 MPH
96H 30/1800Z 39.5N 76.5W 55 KT 65 MPH...POST-TROP/EXTRATROP
120H 31/1800Z 41.0N 77.0W 40 KT 45 MPH...POST-TROP/EXTRATROP

$$
FORECASTER PASCH
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Morning e-mail from Jeff:

Historic storm system heading for the mid Atlantic and NE US.

Potentially life threatening destructive storm surge event for the New Jersey and New York coasts.

Discussion:
The transition of Sandy from a pure tropical cyclone toward more of mid-latitude cyclone has begun. Sandy is still located near the northern Bahamas this morning, but satellite and radar images along with recon data suggest that the system has made the expected turn toward the NNE and this motion should continue with an increase in forward speed. Aircraft data also shows the wind field is greatly expanding with TS force winds extending outward 435 miles from the center with the highest winds located across the western and northwestern flank of the circulation where sporadic deep convection is found.

Across the north Atlantic and the US, the upper air pattern continues to “block” with massive high pressure building over eastern Canada and a strong trough (our cold front) pressing into the eastern US. A shortwave over the western states this morning will swing through the base of the main trough and tilt it from SE to NW over the SE and mid Atlantic starting tomorrow. Sandy will become captured by this titling and instead of pushed out to sea, make a hard left turn (NW) back toward the US mid-Atlantic and NE US coast between the trough to her SW and the blocking high to her NE. Global guidance is in very good agreement on this pattern and in fact has very little spread in the track solution given the complex interactions that will be in place. Models show Sandy moving NW to WNW toward the New Jersey coast and making landfall Monday night or Tuesday morning and then slowing down as she moves inland.

As for intensity, Sandy is gradually taking on more and more mid latitude influences although her center core remains “warm” or tropical. Jet stream phasing with the system is starting to occur with temperature gradient developing on her outer flanks of the large circulation. As Sandy moves northward this process will intensify has the warm Caribbean air mass clashes with a very cold polar air mass resulting in strong baroclinic intensification. Sandy will also be located in the favorable region of the trough and jet stream axis to promote surface deepening of a cyclone. Models continue to advertise “incredibly” low pressures with the ECMWF showing a record 942mb low near landfall on the New Jersey coast which is an astounding 30mb lower than the 1991 Perfect Storm and 6mb lower than anything ever recorded in the NE US.

Given the continued very good model agreement on both track and the forecasted extreme low pressures, confidence is building that an extremely rare powerful storm system will impact the NE and mid-Atlantic coast from Sunday-Thursday.

Impacts:
Major travel disruption is likely as numerous major E coast airports will not be able to sustain operations and this will have ripple effects across the nation. Additionally, widespread power outages and down trees will greatly hamper surface and rail travel across the entire region with widespread and potentially prolonged impacts to commerce.

This will be a long duration multi-day event with prolonged impacts over the entire area from North Carolina to Canada and extending inland into the OH valley affecting some 55-65 million people.

Coastal flooding or storm surge flooding appears to be significant especially for the New Jersey and New York (NYC and Long Island) coasts. The angle of approach this storm will be taking from (SE to NW) strikes the coast at a right angle instead of the usual grazing by of the coast most storms in this region take (SW to NE or parallel to the coast). This direct hit on the coast will drive onshore winds and massive amounts of Atlantic seawater toward the central and northern New Jersey coast and into the “L” shaped New York Bight area of southern New York City and western Long Island (a worst case track for this area, that has never occurred before with this strong of a storm system). The fetch of wind across the entire north Atlantic will drive large waves and surge to the coast and this will last for several high tide cycles. Tides will be at their maximum due to the full moon on Monday. Massive beach erosion is likely with coastal structures experiences significant damage many to the point of total collapse. Seawater inundation will be extensive and widespread and long lasting and in some places potentially record setting. Due to the rare track of this storm, some locations that have never before experienced coastal flooding, may flood with this event.

Winds of 50-60mph with gust to 70-80mph will battered a wide area for 24-48 hours. Expect widespread tree damage and power outages which could rival some of the largest power outages ever in the US. The prolonged nature of the event will result in trees giving way over time as the ground saturates from the heavy rainfall. Winds will be higher in an near tall high rise buildings where funneling will take place. Structure damage will be mainly from trees falling into buildings and to roofs from the wind itself.

Rainfall amounts of 5-8 inches will be common over a very large area with totals of 8-12 inches over New Jersey into southern PA and New York. Isolated amounts of 15 inches are possible as the tropical moisture from Sandy’s air mass crashes into the eastern slopes of the mountains and a stalled frontal boundary. Rainfall of this magnitude over an area of steep terrain will produce life threatening flash flooding and major river flooding.

Ocean seas will be building to staggering heights over the next few days. Already buoys north of the Bahamas have been reporting 30 foot seas, and Wave Watch III guidance is maxed out at 42-48 foot seas over the NW Atlantic Ocean by early next week. The expanding area of strong winds of 50-60mph and the massive fetch of wind all the way from Europe will produce very large swells. Would not be surprised to see reports of wave greater than 50-60 feet over the NW Atlantic. Some of this wave action and energy will be directed toward the US coastline and this will worsen the beach erosion. Large wave setup will also trap water levels near the coast and worsen the coastal flooding threat.

On the extreme SW flank of the storm heavy wet snow will fall over parts of OH and WV with totals of 1-2 feet possible.

Power outages will likely last for 1-2 weeks or longer

Large scale evacuation orders for the New Jersey coast will be underway today with portions of New York also likely requiring evacuation due to the potential for coastal storm surge inundation.
Carla/Alicia/Jerry(In The Eye)/Michelle/Charley/Ivan/Dennis/Katrina/Rita/Wilma/Humberto/Ike/Harvey

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10272012_1245_goes13_x_vis2km_18LSANDY_65kts-956mb-288N-768W_100pc.jpg
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12Z Tracks & Intensity:
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HURRICANE SANDY DISCUSSION NUMBER 21
NWS NATIONAL HURRICANE CENTER MIAMI FL AL182012
1100 AM EDT SAT OCT 27 2012

NOAA AND AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT HAVE BEEN
SAMPLING THE CYCLONE THIS MORNING. THE AIR FORCE AIRCRAFT FOUND
AN AREA OF HURRICANE-FORCE SFMR WINDS TO THE SOUTHWEST OF
THE CENTER AND A PEAK 850 MB FLIGHT-LEVEL WIND OF 91 KT. A
DROPSONDE RELEASED FROM THE NOAA AIRCRAFT IN THE SAME AREA ALSO
SUPPORTED WINDS TO HURRICANE FORCE. THE AIR FORCE AIRCRAFT ALSO
REPORTED A MINIMUM PRESSURE OF AROUND 956 MB FROM A DROPSONDE
AROUND 1200 UTC...BUT THE PRESSURE IS UP A COUPLE OF MILLIBARS ON
THE LATEST FIX. BASED ON THE AIRCRAFT DATA...THE INTENSITY WAS
INCREASED ON THE 8 AM INTERMEDIATE ADVISORY AND SANDY IS ONCE AGAIN
A 65-KT HURRICANE. WHILE SANDY COULD WEAKEN SLIGHTLY DURING THE
NEXT 12 TO 24 HOURS...THE NHC FORECAST KEEPS THE CYCLONE AT
HURRICANE STRENGTH. THE GLOBAL MODELS INDICATE THAT THE CYCLONE
COULD INTENSIFY AS IT INTERACTS WITH A STRONG SHORTWAVE TROUGH
MOVING INTO THE EASTERN UNITED STATES BY LATE SUNDAY...AND THE
OFFICIAL FORECAST SHOWS A PEAK INTENSITY SLIGHTLY HIGHER THAN
THE PREPVIOUS FORECAST. THE CYCLONE SHOULD STEADILY WEAKEN
AFTER LANDFALL.

ALTHOUGH THE MOST RECENT AIRCRAFT FIX SHOWS THAT THE HURRICANE HAS
MADE A JOG TO THE EAST DURING THE PAST COUPLE OF HOURS...THE LONGER
TERM MOTION YIELDS AN INTIAL MOTION OF 030/8 KT. THE TRACK
GUIDANCE IS IN GOOD AGREEMENT DURING THE FIRST 36 TO 48 HOURS.
AFTER THAT TIME...THERE ARE SOME DIFFERENCES AS TO HOW SHARP A
WESTWARD TURN THE CYCLONE MAKES BEFORE REACHING THE EAST COAST OF
THE UNITED STATES. SOME OF THE GUIDANCE...SUCH AS THE GFS...
SUGGESTS THAT THERE WILL BE A CONTINUED NORTHWARD MOTION AFTER 48
HOURS AND THEN A VERY HARD TURN TO THE WEST...MEANING THAT SANDY
WOULD LIKELY COME ASHORE MOVING FROM EAST TO WEST...RATHER THAN
FROM SOUTHEAST TO NORTHWEST AS SUGGESTED BY DRAWING A STRAIGHT LINE
BETWEEN THE 48 AND 72 HOUR FORECAST POINTS. HAVING SAID THAT...IT
IS STILL TO SOON TO FOCUS ON THE EXACT TRACK OF THE CENTER...BOTH
BECAUSE OF FORECAST UNCERTAINTY AND BECAUSE THE IMPACTS ARE GOING
TO COVER SUCH A LARGE AREA AWAY FROM THE CENTER.

NOTE THAT WIND HAZARDS FOR SANDY NORTH OF THE TROPICAL STORM WARNING
AREA ARE BEING HANDLED BY HIGH WIND...STORM...AND GALE WATCHES AND
WARNINGS ISSUED BY LOCAL NATIONAL WEATHER SERVICE OFFICES. GALE
CONDITIONS ARE LIKELY TO FIRST REACH THE MID-ATLANTIC COAST BY LATE
SUNDAY.

FORECAST POSITIONS AND MAX WINDS

INIT 27/1500Z 29.0N 76.0W 65 KT 75 MPH
12H 28/0000Z 30.4N 75.0W 65 KT 75 MPH
24H 28/1200Z 32.2N 73.4W 65 KT 75 MPH
36H 29/0000Z 34.2N 72.1W 65 KT 75 MPH
48H 29/1200Z 36.4N 72.0W 70 KT 80 MPH
72H 30/1200Z 39.8N 77.0W 55 KT 65 MPH...POST-TROP/EXTRATROP
96H 31/1200Z 40.8N 77.5W 40 KT 45 MPH...POST-TROP/EXTRATROP
120H 01/1200Z 43.8N 76.8W 35 KT 40 MPH...POST-TROP/EXTRATROP

$$
FORECASTER BROWN
Attachments
10272012 11 AM EDT Sandy 150615W5_NL_sm.gif
Carla/Alicia/Jerry(In The Eye)/Michelle/Charley/Ivan/Dennis/Katrina/Rita/Wilma/Humberto/Ike/Harvey

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