Ph.D. Student - Earth System Science (UC Irvine), B.Sc. - Atmospheric Sciences (Cornell University)
By: Zachary Labe , 1:39 PM GMT on October 26, 2012
Hurricane Sandy (Nor'easter/Hybrid Tropical Event; October 29-31, 2012
(Courtesy of Penn State EWall)
The upcoming storm event holds many unique characteristics that not only make the forecast difficult, but also will prove challenges for impacts along the entire eastern seaboard. Hurricane Sandy is beginning to charge due north and will continue on a similar trajectory until it begins to hook northwest. This is a very rare and perhaps unprecedented track, which will make any comparison to previous storm systems quite difficult. Given the unique jet stream structure, Sandy is actually expected to strengthen despite encountering land and losing warm core tropical characteristics. This again is very unusual; a few ensemble guidance models depict a nearly 20mb+ drop in surface pressure during this period. The track remains highly uncertain, but we can begin to narrow down the width of the cone to a narrower 200-300mi or so.
While Sandy remains several days away before making landfall, this blog will highlight general threat areas and precautions that need to be taken at this point in time. Given my upcoming schedule, I was only able to put out a full blog this Friday morning. But you can expect me to be actively posting in comments below through Wednesday.
It is important to understand that the location of the landfall will be critical particularly for coastal flooding and storm surge. Certain locations are much worse off for this threat depending on the track of the center of circulation. For the time being, it looks like a track will lead itself somewhere between Ocean City, MD and Sandy Hook, NJ. A few ensembles are farther north towards Long Island and New York City, but given the strength of the block, I am leaning towards a landfall very close to Atlantic City, New Jersey (ACY). The area currently under the highest threat for the combination of wind, heavy rain, and coastal flooding is the region from central New Jersey to northern New Jersey. This area may likely be just northeast of the center of circulation and therefore will be the strongest quadrant of the storm. Given the slow movement, the strong easterly flow will pool water up and along the coast with devasting effects from beach erosion. More on threats and the synoptic setup can be found below.
Remember, the unique setup brings in itself a load of additional problems for areas in the Middle Atlantic and Northeast. The forecast remains uncertain, although the track cone will begin to be narrowed down by Saturday. Stay tuned to the latest updates and for areas along the coast, be sure to heed to local authorities and be prepared to evacuate low lying areas. While Sandy may loose her tropical status, the combination of an anomalous jet structure and bizarre track will be almost as if a stronger and larger hurricane were actually making landfall on the coast. I have seen a great deal of hype by not only the media, but also other meteorological authorities. These statements must be taken with a grain of salt. This is not a worst case scenario and likely not a crippling event. Bottom line is that impacts will be felt over a large region and impact one of the largest concentrations of metropolis in the United States. But conditions are not expected to be any worse than previous destructive nor'easters such as the storm of December of 1992 and Hurricane Hazel. This storm is not going to feature the same variables as the deepening hurricane of 1938 in New England, so impacts will be lessened. All in all though I would not be surprised to hear this is a 1-2 billion dollar disaster with impacts worse than that of last year's Hurricane Irene.
(Courtesy of NOAA)
Keep in mind this is not a tightly wound hurricane. Given the hybrid structure of the storm, impacts will be large and felt over a wide region of the Northeast. In fact tropical storm force sustained winds will be felt possibly from Massachusetts to as far south as North Carolina. Even hurricane force wind gusts may stretch a bit inland. The precipitation shield and associated spiral bands will stretch all the way as far west as Michigan and Ohio. Impacts will be greatly magnified as depending on the exact angle of landfall. Should Sandy make landfall coming from the due west, impacts would be lessened for coastal flooding due to the trajectory of the winds and pooling of water. But under a northwest angle (more likely scenario) water will flood many of the bays and sounds along the Middle Atlantic courtesy of a substantial and consistent easterly and northeasterly flow.
Heavy rain- Flash flood guidance (FFG) is relatively high over the entire Northeast. Despite consistent rain chances each week over the region, rainfall has been relatively near normal. The wettest areas are across the Middle Atlantic, particularly in Pennsylvania. But even in this region, FFG is pretty high. Nevertheless some areas will receive over 6in+ of rain and that will certainly cause at least urban flooding. Sandy will not be one consistent rain shield that is common in nor'easters. It will likely take a structure of a hybrid storm with multiple wide bands that will contain the strongest winds and heaviest rain. The heaviest bands will be to the west of the center of circulation. Currently the heavy rain axis looks to position itself from the Delmarva stretching northeast to northern Maryland and southern Pennsylvania. Highest QPF totals will likely reach 10in+ especially in parts of Delaware, Maryland, and southern New Jersey. Keep in mind the tropical origins of the system despite the time of year being late October. Elsewhere over the Northeast a widespread 2-4in of rain can be expected. The highest threat of flooding will exist as flash flooding and urban areas along with creeks and streams. Major river flooding is not expected at this time given the relatively low levels present. Should QPF increase in the northern tributaries of major rivers such as the Susquehanna, Schuykill, Juniata, and Delaware Rivers, then this threat may increase.
Winds- A tight pressure gradient exists and is highly evident on all upper air and surface maps. A 1035mb high pressure sits to the north near the Gulf of Maine and an anomalous block of upper level heights exists near Greenland. This gradient will enhance the winds over the region from Sunday. Also noticeable on upper level maps is an impressive jet structure on the synoptic scale. A screaming 120knot jet streak near the right front entrance quadrant along with a tight area of divergence aloft will allow for an expanding wind shield that will stretch several hundred miles. Tropical storm force sustained winds can be expected well away from the center of circulation. The strong winds can be be expected just northwest of the center, where gusts may exceed 70mph. Given the time of year, many leaves are off the trees, so wind damage will be less for foliage than if had this had occured earlier in the season. Nonetheless, widespread power outages (millions of people possible) may be expected stretching from New England to the Delmarva. Major cities including Philadelphia, New York City, and the Baltimore to Washington DC corridor can expect maximum gusts upwards of 60-70mph. Sustained winds though will only around 40mph during their height. Along the coast hurricane force gusts may occur.
Severe Weather- Given the time of year, there is significantly less instability both at the surface and aloft. But there remains a great deal of lift and shear, that may allow for a few quick spin-up tornadoes to occur. The area that may under the gun for this threat will stretch from Norfolk, VA north through southern New Jersey. It will be difficult to pick up these areas of rotation using our current NEXRAD radar system, but these possible weak tornadoes will be most likely in the spiral bands as they make landfall on the coast. Farther inland, the threat will decrease due to colder air aloft and less elevated instability.
Storm Surge/Coastal Flooding- I would be getting very concerned if I were living anywhere along the coast from Virginia to Connecticut. This long-duration event in combination with full moon high tides will plague the region with significant coastal flooding and storm surge. It is expected that water levels will exceed Irene values by several feet. I think the highest threat for flooding will be along the Long Island Sound especially in the northwest corner. There water may rise upwards of 8-10 feet and be more representative of a category 2 hurricane than an extratropical cyclone. Also significant flooding can be expected along the barrier islands of New Jersey where many of the sounds and bays will flood as east and northeast winds pool water into the narrow features. This will also be a long duration event given the slow movement as Sandy begins its phase with the trough and hooks west and northwest. Impressive seas and wave heights can be expected, and I am definitely interested in seeing some buoy heights for areas just off the coast. Locations from the Long Island Sound down through low-lying areas in Delaware need to be prepared for evacuations. Farther south into the northern Outerbanks, water levels will only rise 1-3 feet. Major beach erosion can be expected and may cost several million dollars to repair after the event.
Snow- I will admit I have not been following the snowfall forecast as closely as other factors for this event. But it is likely the some peaks along the Appalachians receive a healthy 12-18in of wet snow. Elevations above 3500ft will have the highest threat. Latest models have been consistent in indicating H85 thermals to fall below 0C in association with a cold pocket and Sandy becomes entrapped in the trough. Heavy snow will fall possibly even into a few valley locations into West Virginia and maybe Ohio. Western Maryland is also under the threat zone in Garret County, and perhaps into the southern Laurel Highlands in southwestern Pennsylvania. Most of these locations have already had the leaves fall off the trees, so damage to foliage will be less than the October Nor'easter of 2011. Power outages though can be expected given snow ratios will be at 10:1 or slightly less. Once Sandy begins to pull to the northeast by mid to late week and the trough becomes situated over the area, a northwest flow will allow for widespread lake effect snow showers and flurries over the Northeast especially in the favored snow belts. Many areas will see their first flakes of snow in the November 1-3 time frame from just east of the Appalachians on westward.
"Radar for Central Pennsylvania"
"Radar for Eastern Pennsylvania"
Current Surface Map...
(Courtesy of Penn State EWall)
A sharp cold front is plowing through the midwest and noticed on surface maps by a clear 40F temperature drop. It will continue to march east in association with a steep trough that will begin to become negatively tilted. Anomalous upper level heights near Greenland will act as a block in correspondance with a deep negative NAO to slow down the long waves and general flow. A 1035mb high pressure near Nova Scotia will remain generally stationary over the next few days. Meanwhile a hurricane near the Bahamas, Sandy, will continue track at near 5 degrees north through the day on Friday and Saturday. Increasing vertical shear will begin to tear Sandy apart. This is already noticeable on the first look at this morning's visible satellite given a relatively ragid looking cirrus deck with two concentrated areas of convection. The latest hurricane hunter reports indicate max sustained winds may have dropped to 80 knots aloft with surface winds at sub 60 knots. This is slightly weaker than most operational models have it at this point.
As Sandy continues to move north, she will begin to take on extratropical characteristics and form a hybrid storm. An fast jet streak near 120 knots in association with a vibrant low level jet will help to capture and phase Sandy as she reaches above 30N. Noticeable and impressive divergence aloft in combination with an area of baroclinicity will actually help to strengthen Sandy despite losing its tropical features. This hybrid system is forecasted to drop surface pressure to as low as 960mb as it makes landfall and moves inland. The timing of the phase is critical to the landfall location. Sandy does have an easterly component given the natural forcing of the prevailing westerlies and coriolis, but given the synoptic setup, she will eventually turn to the northwest. I am favoring a landfall just north of Atlantic City, but it is possible for a Long Island hit given this easterly component.
Rising PWATs at near +3SD, given climatology, will allow tropical moisture to flood the region. Meanwhile to the west, continental polar air will leak into the area turning some precipitation into snow across the higher elevations of the western Appalachians.
Sandy will feature a large wind shield and will be a long duration event therefore giving way to high storm surge. Peak height may be over 10ft in a few isolated locations, which may cause major problems given the geographic structure of the Middle Atlantic coastline. This threat is highest from New Jersey up to the Long Island Sound.
As she begins to become captured by the trough, she will slowly begin to move west then north and northeast under a retrograding motion. Therefore wind, surge, and precipitation will plague the northeast for multiple days before coming to an end by mid week.
Current Water Vapor Loop...
(Courtesy of Penn State EWall)
Operational and Ensemble Forecast...
We still have a relatively large spread in the operational and ensemble models. The cone of landfall for guidance is as far south as Norfolk, VA to Long Island, with most models in between favoring the Delmarva up through central New Jersey. Models are having a difficulty in pinpointing the exact timing of the phase with the trough and the strength of the upstream blocking. I am presently favoring a track just in between the ECMWF and GFS. Given the highly parameterized ECMWF and its higher resolution, it lends me to believe that it is overestimating the actual phase (occuring to early) and therefore a bit too south in its track. I also believe the angle of the trajectory on the ECMWF is slightly too westerly and that Sandy will track a tad farther east before eventually turning northwest. The GFS on the other hand is farther north with its expected landfall, but has the tendency to underestimate the blocking to the north which acts like a well and will prevent Sandy from escaping to the east.
The tropical models such as the HWRF and GFDL will have a difficult time in forecasting Sandy given the similarities to a middle latitude cyclone and the complex jet dynamics. They can pretty much be discarded for this event. Ensembles will be very helpful in the forecast for Sandy and both the ECMWF and GFS's associated ensemble means are both just north of their operational partner's forecast.
Trends I would look for on Friday and Saturday include the strength of the block and the timing of the trough as it becomes negatively tilted. I am predicting we see the ECMWF shift a bit to the north in its forecast track as it may be underestimating the easterly component for Sandy. While I am presently favoring a landfall near Atlantic City, NJ or a tad north, I cannot rule out a landfall along Long Island. I do not expect the landfall to occur any further south than Delaware.
Forecast Model Links
-NAM model 12z...Link
-GFS model 12z...Link
-NMM model 12z...Link
-SREF model 9z...Link
Severe Weather Links
-Atmospheric Soundings Skewt T charts...Link
-SPC Mesoscale Analysis Pages...Link
-Public Spotter Reports for State College NWS...Link
-Severe Weather Model Forecast indices...Link
-Severe Weather Parameter Definitions...Link
-Automated Pennsylvania Rainfall Recording Stations...Link
-Flash Flooding Guidance...Link
-HPC Forecasts for Excessive Rainfall...Link
-Hydrology Predictions for Lakes, Rivers, and Streams...Link
***Stay tuned and discuss below! Please... when reporting observations, include your exact location in every comment. It makes it very helpful for others to prepare for what they can expect in a later time.
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"Lower Susquehanna Valley Doppler"
(Courtesy of WGAL)
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