Friday, November 09, 2012

Sandy's Size Mattered More Than Its Wind

Despite Sandy being a 90 mph hurricane at its peak wind intensity, its size was large and that large geographic coverage helped create a storm that contained more total energy than Katrina in 2005.

One of the measurements in determining storm intensity and strength is IKE -- Integrated Kinetic Energy. It's a metric that measures how far tropical storm (39+ mph winds) travel from the center of the storm. This, unlike Saffir-Simpson, gives a true measure of tropical (or even nor'easter) punch because larger tropical cyclones can rack up higher amounts of IKE despite having lower wind speeds.

Graphic courtesy of Capital Weather Gang (capitalweather.com)

The IKE for Sandy was the second largest of any tropical (or hybrid) cyclone to make landfall since the late 60's.  The only storm that had a higher IKE ranking was Isabel in 2003, which was another massive storm with a very large wind field.  Isabel also knocked out power to 500,000 people in Southeast PA's PECO territory.

Sandy's ranking of 140 terajoules is twice that of the Hiroshima bomb.  Strong storms -- tropical and not -- often contain the equivalent of an atom bomb in energy due to tremendous wind energy they generate due to pressure differentials between the low point and the surrounding atmosphere.

Saffir-Simpson is somewhat of an imperfect metric in terms of measuring storm size and overall impact.  Camille in 1969 had half the IKE rating that Sandy did.  Not to dismiss Camille (it was a nasty storm that leveled a chunk of the Mississippi and Alabama coastline) but its size was much smaller and as a result its impacts were minimal geographically in comparison.  Charley in 2004 was a Category 4 at landfall but had one-sixth Katrina's IKE rating because the wind radii of tropical storm force winds was just 70 miles from the center at landfall.  Comparing Charley to Sandy, Sandy's tropical storm radii was nearly 400 miles from the center and its IKE rating was one seventh that of Sandy's.


Graphic courtesy of Capital Weather Gang (capitalweather.com)


Wind speed matters to a point.  Size matters more.   A larger storm can generate a larger geographic impact of storm surge, which in Sandy's case is partly why the surge 100 miles to the north of Ocean City was as large as it was.  The other factor for North Jersey and New York was the coastal topography of the New York City area (right angle).  Water was pushed west through Long Island Sound and on the South Shore of Long Island into New York Harbor or along the Jersey coastline without an escape avenue.

Those south of the landfall point did not get the surge impact at the same extent North Jersey did (you got back bay flooding the barrier islands from the winds on the storm and *some* coastal flooding, but rains were much more plentiful in Wildwood than in Seaside).   The "It Could Happen Tomorrow" Scenario did...but it happened with a landfalling 75 mph coastal hybrid storm and not with a Category 3.  Why?  Because Sandy's size was impressively large and because it hit the Jersey Shore at a "great" location to cause damage for those north of the landfall point.