Wednesday, October 24, 2012

Sandy, The Perfect Storm, and Hybrid Storms

Around Halloween in 1991 the combination of a mid latitude low and the remnant energy of Hurricane Grace combined to form the Perfect Storm, the "infamous" hurricane/hybrid storm system that lashed New England with wind and some rain. It grazed Philadelphia with clouds but a fair amount of wind.

While this storm is being dug out of the moth balls because of similar meteorological forces at play, there are some things to keep in mind over the coming days as you get inundated with model hype.

Hybrid storm systems that fuse mid atmospheric energy from troughs with tropical energy or some tropical "fuel" can be large, powerful storms that cause impact over a wide swath of real estate.  They are coastal storms but with a bit more moisture and more fuel.  Ida is a good example of this in 2009 -- a tropical entity that phased with nontropical energy to create a potent coastal storm.  Those at the Jersey Shore know what Ida did to them and know it wasn't a fun storm in the least...and that storm was centered near Hatteras as its northernmost venture.

Sandy will very likely not be a hurricane by definition when it hits our region.  Water temperatures are below 70 degrees off the Jersey coast so by "purely" tropical definitions it will not be a 'cane at our latitude since tropical systems rely on warmer water to survive and thrive.  However, because the storm is relying on energy in the atmosphere (aloft) and the digging trough to strengthen, it will be one of these hybrid storm systems that will impact a large swath of real estate.   Will it be as strong as the Euro and Canadian are hyping it out to be, with the pressure equivalent of a Category 3 hurricane?  Very likely not.  The Euro missed on Irene's intensity by quite a bit four days out (having a 930mb ish system at landfall when it was near 960 at landfall). To me, the 930/940 mb predictions of pressure from the Euro a bit unrealistic and predictions you should not get wrapped around.  The Euro and Canadian have a tendency to overdo storm intensity.  Track is another story, especially on the Euro, for reasons we talked about earlier today.

Will it be a strong storm?  Yes...even if we take 30 mb off of the Euro-hype, you're still looking at a 960-970 mb storm, which is still quite low for a pressure center.  Unlike with tropical systems, where the strongest winds and heaviest rains are right near the center, the strongest winds and heaviest rains will likely spread out away from the center and it may look like a hybrid between a nor'easter and a hurricane on Monday or Tuesday based on location.  Even if low pressure intensity isn't the be all/end all factor with this storm, the location of the low does matter, however, as does the track of the storm.

An earlier "phase" or combination of tropical energy with the digging trough to Sandy's west will result in a faster bend back of the storm and take the storm closer to our region.  More important, if the phase occurs soon enough the storm could be pulled back west very close to our region...which puts the worst coastal flooding impacts into Jersey and perhaps even Delaware.  Rains would be heavy, with several inches possible.  Ida brought five inches of rain to Atlantic City and less than an inch to Philadelphia.

On the flip side, if that phase is slower to take place...if the trough dig is a bit slower and Sandy moves a bit slower, a scenario closer to the GFS and Canadian could verify.  This scenario would result in a lesser impact for us -- wind, some rain, but the worst of the worst goes to New England.  There would be some coastal flooding in New Jersey and Delaware, some beach erosion, but the worst impacts are up the coast and not near us.  The GFS is tracking Sandy farther east compared to the Euro (but is much closer than its past model runs).  However, it does link up with Sandy a bit later and pull the storm back into Eastern New England a la the Perfect Storm scenario.

There's a lot that can still shake out over the next five days.  Coastal folks can start preparations for coastal flooding -- that looks pretty likely regardless of scenario.  Wind and rain are likely in either scenario...the closer track ramps up the potential for inland flooding from heavier rainfall and stronger winds in our region, however.  Who gets the "worst of worst" impacts of the storm remains up in the air.  Could be Jersey, could be Maine, could be Atlantic Canada, or somewhere in between.