COASTAL IMPACTS vs SAFFIR/SIMPSON SCALE

I have written blogs on the Saffir/Simpson hurricane scale in the past, but felt it was time to rehash some of the points I made before, especially after the recent coastal devastation associated with hurricane Ike. I have heard and read much lately about how Ike was only a CAT 2 yet it did so much damage, and how people did not evacuate because Ike was not a "major hurricane". These are disconnects between the basic Saffir/Simpson hurricane scale and resultant coastal and inland impacts. I digress for a moment to say that the Saffir/Simpson 5-category scale is based on the fastest tropical storm or hurricane wind speed that can be found, measured, indirectly measured or inferred from meteorological data and reasoning. That maximum wind speed by itself does NOT have a direct relationship to the water rise at the coast, wave heights at the coast, beach erosion and inundation at the coast, or rainfall at and inland from the coast. And the wind speed ONLY applies to the tiny, to the moderate, to the medium, to the large or to the huge area over which it is assumed to be blowing.

Let me lay out a very simple explainer matrix that shows the multiple elements responsible for what I have condensed into my four primary land impacts, namely; wind, waves, water rise and rainfall. I use water rise here and NOT "storm surge" because water rise is what floods things on land, and surge is but one component of the water rise.

IMPACT	CAUSE(S)
WIND	Wind strength at landfall
	Wind gust strength at landfall
	Spatial area of damaging winds
	Strength of structure being impacted
	Elevation of the land/object
WAVES	Wind Speed
	Distance over which the wind blows
	Duration of time the wind blows
	Coastal bathymetry
	Pre-existing coastal erosion state
WATER RISE	Wind speed in shallow water to coast
	Coastal location and bathymetry
	Breaking wave heights
	Inverse barometer effect
RAINFALL	Tropical cyclone forward speed
	Tropical cyclone size
	Land geography/orography/topography
	Pre-existing land moisture conditions

Note that I have omitted the many details on how to calculate "impacts" at a coastline because that would take hundreds of pages to discuss in detail. But in this simple "cause" section you can see I list only 4 causes (in bold) that are related directly to maximum wind speed in the tropical cyclone. I list 13 causes for these impacts that have nothing to do with the maximum wind speed in the tropical cyclone (not in bold).

As you can clearly see, what happens at the coast and inland to a large extent has not much to do with the maximum wind located in some small sector of a tropical cyclone. One must examine all the contributors to the four impacts I list above, then run models that are able to predict the magnitude of each impact. The size of the circulation and the size of the strong winds is as important if not more important that the single maximum wind in the circulation for many of the impacts listed above. Watch The Weather Channel, as we will do our best to show maps of coastal and inland impacts based on at least the list of causes shown above using our models. And remember do NOT focus simply on the Saffir/Simpson category of the hurricane coming your way as the impacts can be far greater or far less that what that category might imply.