Time For a New Hurricane Rating System?
Nothing strikes fear into people along the Gulf and Atlantic coasts quite like the words "Category Five." Yet, two of the more destructive hurricanes on record -- Ike and Katrina -- were nowhere close to Category 5 status when they made landfall.
Ike was a strong Category 2 storm when its eye reached the Texas coastline during the early-morning hours of Sept. 13, with sustained winds near 110 mph, just 1 mph short of the Category 3 threshold. And Katrina was an upper-end Category 3 storm with sustained winds just over 125 mph when its center came ashore in southeast Louisiana on Aug. 29, 2005.
While the wind speeds of Ike and Katrina at landfall were nothing to sneeze at, it was the storm surge -- the wall of water pushed ashore when a hurricane's eye makes landfall -- generated by both storms that did the most damage.
Keep reading for more on why it might be time for a new hurricane scale. Also, see our full forecast into the coming work week. See also NatCast for the forecast for tonight's game and don't miss SkinsCast for Sunday's game.
The familiar Saffir-Simpson Scale, in use since the early 1970s, rates hurricanes based solely on observed wind speed. The system is understood well by the media and public, and is often an accurate indicator of how damaging a storm will be.
But not always.
While storms with extreme winds tend to produce extreme storm surges, and storms with weaker winds tend produce weaker storm surges, sometimes the two factors are not as well correlated. For some hurricanes, the size of the storm may enhance or lessen the storm surge independent of wind strength -- the bigger the storm, the greater the storm surge, and vice-versa.
In the case of Katrina, tropical storm-force winds extended 230 miles out from its center, and storm surges ended up being as high as 25-28 feet. Ike's wind field was even more impressive, with tropical storm-force winds extending 275 miles out at one point, though its maximum storm surge of about 15 feet was less than predicted.
In the April 2007 issue of the Bulletin of the American Meteorological Society, Mark Powell (NOAA) and Timothy Reinhold (Institute for Business and Home Safety) proposed a new hurricane scale based not only on the speed of a storm's strongest winds, but also how far out tropical storm-force winds extend from the center of the storm. In science speak, the proposed scale is based on something called "Integrated Kinetic Energy," or IKE (yes, quite a coincidence with the name and all).
As Jeff Masters of Weather Underground pointed out in the lead up to Hurricane Ike, Katrina and Ike scored a 5.1 and 5.2 on this 1-to-6 scale, respectively.
The National Hurricane Center does indeed include in its public forecasts an estimate of how high a storm's surge will be. But assigning some sort of a scale, numerical or otherwise, to the predicted storm surge may help to better communicate the threat to the public at large.
I'd encourage the meteorological community and the media to slowly phase the IKE-based scale, or something similar, into operational use, and possibly eventually phase out Saffir-Simpson, which has served society well but doesn't always tell the whole story.
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