East Coast High Impact Hurricane/Post Tropical Storm Sandy

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East Coast High Impact Hurricane/Post Tropical Storm Sandy

Postby srainhoutx » Fri Oct 26, 2012 6:43 am

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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Re: East Coast High Impact Hurricane/Post Tropical Storm San

Postby srainhoutx » Fri Oct 26, 2012 7:24 am

HPC 5 Day QPF Forecast:
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Re: East Coast High Impact Hurricane/Post Tropical Storm San

Postby srainhoutx » Fri Oct 26, 2012 7:37 am

10262012 1139Z Sandy latest.jpg
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Re: East Coast High Impact Hurricane/Post Tropical Storm San

Postby Andrew » Fri Oct 26, 2012 9:26 am

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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Re: East Coast High Impact Hurricane/Post Tropical Storm San

Postby michmich » Fri Oct 26, 2012 9:39 am

I'm surprised there's not more discussion about this. Sandy looks like one crazy beast.
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Re: East Coast High Impact Hurricane/Post Tropical Storm San

Postby srainhoutx » Fri Oct 26, 2012 9:49 am

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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Re: East Coast High Impact Hurricane/Post Tropical Storm San

Postby srainhoutx » Fri Oct 26, 2012 10:18 am

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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Re: East Coast High Impact Hurricane/Post Tropical Storm San

Postby Karen » Fri Oct 26, 2012 10:24 am

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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Re: East Coast High Impact Hurricane/Post Tropical Storm San

Postby srainhoutx » Fri Oct 26, 2012 10:28 am

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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Re: East Coast High Impact Hurricane/Post Tropical Storm San

Postby unome » Fri Oct 26, 2012 10:34 am

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

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