Some science behind the upcoming storm (and why people in the know are making a big deal of it)

So, why is everyone making a big deal about the upcoming storm? Besides the obvious vulnerabilities to our Sandy-damaged shorelines and communities (ocean and bayside areas will be vulnerable to coastal flooding, erosion, and wash-over events due to increased water levels and wave heights; low-lying areas inland may also be susceptible to flooding from nearby creeks and even storm drains), there are a number of variables that are coming together that may have cumulative (bad) effects.

First is the fact that it looks like the storm looks like it is going to have tight circulation, with an “eye” and the appearance of a tropical storm/hurricane, which means conditions may mimic the effects of one as well. Here is a screen-grab of the wind prediction posted over at magicseaweed.com:

Because it looks like this storm is going to eject somewhere off the Mid-Atlantic seaboard and be slow to move off, it is likely that the tri-state area is going to be on the “wrong side” (North) of the storm’s center, receiving strong NE-NNE-N winds for a good period of time, maximizing wind, waves, and storm-surge.  This means that nearshore waters and back-bays will likely have trouble draining as the tidal ebb out to sea will have to fight a continued surging of water towards land.  Again, I’ll post a screen-grab from magicseaweed.com illustrating this point:

The good news is that we are between the new and full moon states at the moment, which means the storm surge won’t have too much of an assist from the lunar tide.

 

Now, let me introduce a little equation punctuated with some humor:

(+PNA)+(-NAO)+(-AO)= OMG!

(I added the “OMG!” for comedic effect, but the three variables on the left side of the equation are legit)

 

PNA

The PNA (Pacific/North American Teleconnection Pattern) is a driving factor in storm formation in the northern hemisphere.  Associated with the strength and location of the East Asian Jet Stream, it encourages or suppresses storm formation.  A –PNA brings warm weather up from the South, which encourages tropical development (this is the mechanism by which Hurricane Sandy gained strength as she moved up the Eastern Seaboard), while a +PNA state brings cold weather down from the Arctic and fuels winter storm development.  We are currently in a strong +PNA.

 

AO

The AO (Arctic Oscillation) sets up either warm air over the eastern half of the United States during its positive phase or allows cold, dry arctic air to plunge southward during its negative phase.  This plunging of cold, dry arctic air can fuel developing winter coastal storms.  A shift from a positive to negative AO at precisely the “right time” set up conditions to spawn a Nor’easter that then fused with Sandy, resulting in her transformation from a warm-core hurricane to cold-core hybrid storm) as she approached the eastern seaboard.  This is what appears to be setting up for this mid-week storm (not a hybridization, but rather the development of a true cold-core Nor’easter).

 

NAO

The NAO (North American Oscillation) is part of the Arctic Oscillation and is another strong driving factor in storm movement in the Atlantic basin.  A +NAO leads to increased westerly winds around the arctic and keeps cold air constrained to higher latitudes.  Storms are allowed to move freely, and if a strong Bermuda High is at work, they latch onto it and ride it like an escalator into open water.  Conversely, a -NAO results in suppressed westerly winds, allows cold Arctic air to slip south, and allows a “blocking high” to setup over Greenland.  This blocking high, true to it’s moniker, hinders storms from moving off to the northeast; they get “stuck” against the coast, and if a cold-core storm and fed an ample supply of cold arctic air (see AO, above), continue to churn (throwing swell and surge against the coast).  This –NAO is what happened during Sandy, and what is happening now; this storm will likely get held against the coast for an extended period of time by this blocking action.

 

Hopefully that explains some of the science behind why this storm is the talk of the town.

On a final note, looking back to the coastal flooding we experienced on December 27th, which was a news-worthy event in itself as it flooded out a number of homes in low-lying areas that had never been flooded out until Sandy came along:  Unlike the upcoming event, it came during an extreme lunar tide, so its surge had a bit of additional help in that respect.  That said, it was under a +PNA, -AO, +NAO state, so while a broad, slow-moving storm, it had a clearer path out to sea (thanks to less blocking) than this one will likely have.  Regardless of these minor differences, the similarities between the two systems are enough to serve as a heads-up regarding what we may soon experience.