Hurricane Ike, Image: NOAA

When Hurricane Ike slammed into the Texas coastline in September 2008, hurricane forecasters rated it a category 2 hurricane on the Saffir-Simpson scale with maximum sustained winds of 110 miles per hour. The storm surge associated with Ike topped 15-20 feet. If you used the Saffir-Simpson scale as a guide, the storm surge associated with Ike should have been about 6′. (See the graphic below.) The mismatch between the wind speeds generated by the storm and the associated storm surge have led the National Hurricane Center to drop storm surge from the widely used scale.

Old Saffir-Simpson Scale, Image: NOAA

The Saffir-Simpson scale was developed in 1971 by engineer Herbert Saffir and National Hurricane Center Director Bob Simpson to help forecasters explain the potential damage from a hurricane to the public. It was mainly designed as a way to explain what damage would occur to structures if a hurricane hit with 75 mile per hour winds, 95 mile per hour winds, 110 mile per hour winds, etc.  After the scale was developed, forecasters realized storm surge was a significant part of the damage from a hurricane, and they tried to come up with the height of the storm surge associated with different wind speeds. Unfortunately, it has led to errors in forecasting and misleading the public. The effect of storm surge on a coastline depends on the strength of the winds, the direction of the storm, the topography of the coastline, and the bathymetry (or topography of the coastline under the water.) Now, individual weather service offices, as well as universities, produce individual storm surge forecasts for each storm depending on the strength of the storm and its track. Here are the guidelines given today by the National Hurricane Center for the now called Saffir-Simpson Hurricane Wind Scale: