WRAL WeatherCenter Blog

Not your father's hurricane scale

Posted May 25, 2010 10:55 a.m. EDT

When folks think about hurricanes, one of the first things that comes to mind is wind, and lots of it. For years, the National Hurricane Center has categorized hurricanes by using the Saffir-Simpson Scale. This scale attempted to match wind speed, atmospheric pressure, and storm surge thresholds into the same category.  What we found over many years, though, is that storm surge is a function of much more than just wind speed, and that wind speed can be a function of much more than just the lowest pressure in the center of the storm.

So this year, the Saffir-Simpson Scale will apply ONLY to wind speed. Now, do we only have to worry about wind speeds when those winds achieve hurricane force? I’m afraid not. Remember, with a severe thunderstorm, the winds need only be a minimum of 58mph, far below the 74mph needed to classify a storm as a hurricane. Thus, a strong tropical storm can do just as much damage as a severe thunderstorm.

One thing we all learned when Hurricane Fran blasted through Raleigh back in September of 1996, is that the strength of the wind gust only tells part of the story. One gust to 60 mph is very different than gusts to 60 mph which occur over and over again for hours on end. It’s that relentless pounding over a period of time that really does the damage. Thankfully, we know days in advance that a tropical storm or hurricane may be on the way, whereas tornadoes give only a fraction of that warning time.