Posted by: coastlinesproject | October 23, 2012

Shades of the Perfect Storm, TS Sandy could move west expect erosion along East Coast.

The plot below, courtesy of Weather Underground, shows the forecast situation as of this afternoon.
The white line is the GFS model forecast, the rose lines are the forecasts from the GFS ensemble members.
Usually, there is a rough consensus in the general direction of the forecast tracks and the
key issue is the size of the “cone of uncertainty”.  Sometimes, though, we can have a bi-modal distribution of solutions, as you see in the
forecast beyond 3 days.  Sandy is either out to sea or smacks into the East Coast.  The remainder of the hurricane forecast
models are split more or less along these same lines.

The reason for the bi-modal forecast, is that Sandy, as it moves northward, will become less tropical in nature.
This “extratropical transition” phase is not well understood and is the object of ongoing research.  In a nutshell, rather than
moving like a spinning top on an uneven floor like tropical systems do, the extratropical storm is more strongly
affected by larger scale circulations.  In this case, a disturbance expected to drop into the Midwest later this week
will either push it out to sea, or, if the disturbance is strongly spun up, will grab Sandy and shove it westward.

So, interests from HAT northward have to watch Sandy very carefully.  Our most reliable models are split
on the forecast track after Sandy gets north of the Bahamas.    Note that if it re-curves west, shades of The
Perfect Storm, it will be moving fairly slowly and you will have adequate time to prepare.  On the bad
side, it will be moving slowly so erosion will be intense.

-- 
William F. Ryan
Department of Meteorology 
The Pennsylvania State University

"If we begin with certainties, we will end in doubt, 
but if we begin with doubts and bear them patiently, 
we may end in certainty"
Francis Bacon

Read more in Storm Surge and Beach Wars; 10,000 Years on a Barrier Beach. See UPNE and Strawberry Hill tabs at the top of this page.
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