Tuesday, October 23, 2012

Sandy's Voyage Into the Unknown

We still have a rather wide buffet of computer guidance spread before us regarding the future path of Sandy. Sandy's still in the Caribbean, still several days away from possibly impacting the East Coast.  Sandy is slowly intensifying and probably reaches hurricane intensity prior to Jamaica and Cuba.

After that, the uncertainty ratchets up dramatically and the forecast spread is pretty wide.  The operational GFS and Euro are the benchmarks with the storm, about 500 miles separates the two models next Monday night and Tuesday morning regarding where Sandy goes.  The GFS takes Sandy near Bermuda but links its moisture into the advancing trough, too late for a full connection/phase/latching on that the European computer model has hooked onto yet again.  The Euro brings a strong storm northwest into Long Island in that late Monday night/early Tuesday morning timeframe...and as of now would be the "worst of worst" scenarios that the models are painting for the East Coast as a whole for early next week.  More on it in a little bit.

The Canadian is still showing a rather strong storm -- very similar in location and placement to that of the Perfect Storm in 1991, although modeled much stronger than what the '91 event was in intensity.  Canadian likes to overintensify storms but the location is a compromise of sorts from the GFS and the Euro, splitting the uprights.  While it would be breezy to windy here, the worst of worst impacts would be felt across eastern portions of New England and Atlantic Canada.
Lending some support to the Euro camp is the GFS ensemble guidance mean, which shows a track offshore and in very close agreement to the Euro computer ensemble mean.  Ensemble modeling is a variant of the computer model that's run -- slightly different input, slightly different output based on the same algorithms.  Both the Euro and GFS ensemble mean have a coastal hybrid that tracks parallel to the East Coast, passing close enough to increase wind and rain risk along the East Coast for Sunday night and Monday.   The ensemble modeling mean is a nice fallback to help sway or influence forecast thinking -- and in this case they tend to support the "storm" over "no storm" camp.  They aren't fool proof, though!

If the worst of worst scenario plays out (Euro), the "landfall" of the center of the hybrid storm would occur over the Hamptons late Monday night, bringing strong winds over Southern New England and Cape Cod, plus much of Long Island.  Locally, the Shore would get hit very hard....we would get rain and wind but the worst of the effects would be to our east and northeast if the Euro scenario played out perfectly.

The farther east the center tracks from Philadelphia, the less the impact.

There are pretty much three scenarios that are on the board at this point:

1) Out-to-sea...no link with the approaching trough...and Sandy scoots on through the Atlantic as a powerful nontropical storm early next week.  We get a run of the mill frontal passage on Saturday night into Sunday and nice weather.  The blocking high would need to be a bit weaker over Newfoundland and allow the front to scoot through.  Sandy would also need to be a weaker storm than what both models are indicating it will be after it passes Jamaica and Cuba.  A weaker storm would miss the interaction with this digging trough next week.

2) A brush or close approach where the storm stays a bit out to sea but gets captured a bit later than the Euro scenario and eventually gets blocked in by the Newfoundland high we talked about in past posts.  This would create greater impact for Nova Scotia, Maine, eastern Massachusetts.  However, we just deal with breezy conditions and perhaps some showers.  The front sneaks through in time and the link with Sandy's nontropical entity happens too late to directly impact us.  Essentially, the Canadian model outlined above.

3) A strong coastal storm that stalls out, moves slowly, and parks itself near the East Coast.  This would be the worst of worst scenario...if the "landfall" of the hybrid is closer to our region (NJ or the Chesapeake) the impacts would be a lot worse locally than if the landfall is over the Hamptons or Cape Cod.  However, this would create the most disruption for the entirety of the East Coast out of the scenarios on the table.

The timing and interaction between this digging trough and Sandy's drift north is critical -- if the two link up, the better the odds for a big storm.  A faster trough, a weaker storm could result in nothing...or one of the two could result in something like the Canadian (perhaps a nudge east or west).  There is still lots of uncertainty with exactly how things play out but be prepared for the possibility of a storm near or along the East Coast early next week.