Blockbuster in the Making – Not Ready to Bet

Continuing my commentary on the potential for a major east coast weather disaster, I thought I would add a few points of clarification and a comment about the at risk areas:

First, on those pesky computer models and the reasons for the uncertainty with this storm:
  • Even in models which produce the big storm, the result stands on a razor’s edge.  Everything hinges on how far SE and how intense the arriving short wave that should be approaching the Appalachians by Sunday evening can get and how quickly it gets there.  A little too fast, and it boots the hurricane out to sea before it has a chance to undergo extratropical transition, meaning the threat would shift toward Bermuda and then possibly the Canadian Maritimes.  To slow, and the trough doesn’t acquire the depth and sharpness needed to pull the storm back toward the coast and it moves harmlessly offshore, giving us a light brush and some nasty surf.  Even slower, and the storm actually has an opening to make landfall in the Carolinas, though this is unlikely.  On top of that, the precise intensity of the storm will help to shape the blocking ridge in its path and also to pull in energy from the west.  A stronger storm could expedite the deepening of the trough over the east and build the block further, leading to a westward path.  A weaker storm would most likely never come close to land.
  • By no means do all of the models get this storm onto land.  The ensemble of global predictions is placing more emphasis on the western solutions at the moment, but not all of the players are on the field for this high stakes game, so it’s too early to claim model consensus.
  • Our models VERY poor at capturing the move from tropical to extratropical cyclone and getting the thermal structure of the storm right.  And in this case, how warm the system is aloft could be hugely important to its track.
Now…Folks who should and should not be worried:
  • The current threat is to Florida, where very high seas and tropical storm conditions will continue for the next couple of days.  Those outer bands of heavy rains and squally winds will impact the Carolina coasts as well as we head into Friday and Saturday.
  • The threat for a big news maker is north of a line from Norfolk to Baltimore to Pittsburgh to Detroit…it is not likely to be a big deal in DC or Richmond as it would be exceedingly rare for a system to cut back that far west that quickly this late in the tropical season.
  • The threat for a catastrophic solution is centered around Long Island and New York City…if it does not hook back to the west until it is further north, it would likely be a weaker storm as it would be dealing with a lot of wind shear before properly phasing with the polar jet stream.  If it hooks west too early, the coast line is not shaped in such a way as to merit a ton of concern about catastrophic surge. But it if comes ashore over Long Island of Coastal New Jersey, the surge, wind and flood damage could be history-making and cost billions of dollars, because these are the tracks that favor the strongest low and the most unfriendly coastal morphology.  A 6 foot surge will flood the subway tunnels in NYC…this storm could easily top those levels if it comes far enough west.
So keep that in mind as we wait and watch.
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