ACE Index May Be Better Gauge Of Seasonal Activity

While I was the Director of the National Hurricane Center (April 2000-January 2007), I was often invited to speak at various local, state, national and international hurricane conferences. Over my 34 years at the NHC, I was fortunate enough to make many friends who work in various areas of hurricane preparedness, response, recovery and mitigation. I found the initial responses I would get when seeing some of these friends at the conferences quite interesting. Rather than hearing Hi” or “How’s the family?”, I would usually be greeted with something like “What kind of a hurricane season are we going to have?”

Most people want to know how many storms, hurricanes and major hurricanes are expected. One thing that has always bothered me about this, however, is the fact that a tropical cyclone could be designated a tropical storm or a hurricane for a few hours and still be counted. One of those short-lived systems would get counted the same as a major hurricane that lasts days and days. A more valid measure of total seasonal activity is something called the Accumulated Cyclone Energy (ACE) index.

The ACE index is a wind energy index, and is defined by the National Oceanic and Atmospheric Administration (NOAA) as the sum of the squares of the maximum sustained surface wind speed (in knots) measured every six hours for all named systems while they are at least tropical storm strength. The ACE index accounts for the intensity and duration of storms and hurricanes. NOAA forecasts the ACE and compares it to the median ACE value from 1951 to 2000. An above normal season can then be defined by an ACE index value well above the median ACE value.

For 2007, the ACE index is expected by NOAA to be in the range of 140 percent to 200 percent of the median. And it is significant to note that NOAA’s recently updated Atlantic Hurricane Season Outlook is saying that there is an 85 percent chance that 2007 will have above normal activity. This may sound confusing, but the bottom line is that NOAA is expecting a lot of tropical storm and hurricane activity yet to come in 2007.

Hopefully, residents of South Florida will use the updated Atlantic Hurricane Season Outlook as motivation to get prepared. As we head into the peak of the hurricane season, now would be a very good time to dust off your hurricane plan and know exactly what to do if you need to execute it.


One thought on “ACE Index May Be Better Gauge Of Seasonal Activity

  1. Pingback: 2009 Hurricane Season Forecast « Cloudy and Cool

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