October 23, 2012
The 2012 Hurricane Season count has now climbed to 18 ‘named’ storms, with T.D. #19 expected to be upgraded to “T.S. Tony” -- the season’s 19th named storm -- later tonight or tomorrow.
19 ‘named’ storms would tie the number of storms for 1995, 2010, 2011 and way back in 1887. And 19 ranks as the third most active season on the record books for the Atlantic Basin, topped only by the 20 (‘nameable’) storms of 1933 and the mega-active 2005 season (28 ‘named’ storms) when we ran through the alphabet and had to turn to Greek letters for names.
(In case you are wondering, with 38 days to go and with a storm being ‘named’ after November 1st during four of the past five seasons, it is very possible that we could see yet another tropical cyclone even after T.D. #19's upgrade to ‘Tony’ before season’s end.)
A look back at the season predictions from several renowned forecasting teams suggests that all of the hurricane prognosticators have been caught off-guard, again. A collective average of the 2012 predictions from these forecast teams as of the first week of June yields something on the order of 12-13 ‘named’ storms, with 6-7 becoming hurricanes, and 2 of those hurricanes reaching ‘major’ intensity (Category 3 or higher).
While there has only been one ‘major’ Atlantic hurricane thus far in 2012, the forecasts for storm numbers clearly fell short. And to be honest, this is at least the third consecutive season where the predictions under-estimated the number of storms to earn a ‘name.’ Yes, the science has a long, long way to go. But the science continues to improve and some aspects of the forecasts for 2012 weren’t completely amiss. Storm numbers are one thing, but there are other ways to measure activity in a hurricane season.
Some tropical experts prefer to focus on the collective storm energy produced during a storm season. One measure of this storm-season energy is defined by the ACE -- the Accumulated Cyclone Energy index. The ACE is a cumulative energy approximation, combining a measure of the peak sustained wind speeds of individual storms with their durations as tropical storms or hurricanes. An advantage of the ACE in terms of a season’s collective energy is that the ACE accounts for powerful and/or long-lived storms which can generate far greater energy than two, or even three, weaker systems.
In general terms, seasons with ACEs greater than about 110 are deemed as demonstrating “above normal” activity, while ACEs below 65 are “below normal.”
The table provides a summary of the eight “busiest” hurricane seasons based on storm counts. (Since ACEs have only been calculated back to 1950, we have no estimates for the 1933 or 1887 seasons.)
Not surprisingly, the mega-season of 2005 also shows the greatest ACE. But on comparing 2012 with other ’19-named’seasons, the collective storm energy of 2012 is lower, although 2012 might surpass 2011 before the season ends. And note how much lower 2012 is compared to 1969 (Remember, 1969 had 12 hurricanes, 5 as 'majors,' including one named Camille!).
When we look at teh details of 2012, we find that nearly one-quarter of the season’s total ACE is attributed to a single storm -- the long-lived Nadine, a storm that is tied for second in terms of the total number of days in the Atlantic Basin at tropical-storm strength or greater.
So, while the storm-count projections fell short, the 2012 season is not that far “above normal” in terms of the ACE.
In the final analysis, however, some might argue -- and with good reason -- that the best measure for tropical activity deals with impacts and landfalls. If that’s your way of thinking, then Isaac makes the 2012 season a real monster for far too many WAFB communities!
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