Wednesday, November 30, 2011

Recapping the 2011 Atlantic Hurricane Season

When we look back on the 2011 Atlantic Hurricane Season, the memory that will certainly stand out most will be Hurricane Irene (pictured at left and below). But while this season finally did see the US getting hit again by a hurricane, overall it was an odd, odd season.

First off the numbers...
19 Tropical Storms
7 Hurricanes
3 Major Hurricanes

A normal year (1966-2009 per the NHC website) would feature a slashline of 11.3/6.2/2.3. So you can see this year featured well above average activity. Using those statistics alone, you'd surmise it was one heck of a year. And by the numbers, sure. But there's a better way to gauge just how busy the tropical season was, and that's called Accumulated Cyclone Energy...or ACE.

Dr. Ryan Maue tends to do a great job archiving this information and keeping it updated throughout the season. Almost like a weekly normal for me, his site is another one of those "must bookmark" weather sites. Anyway, ACE is computed by a formula which takes into account the strength and duration of strength of the you aren't just dealing with a "count." According to his website, assuming we have no more named storms, the North Atlantic Hurricane Season's ACE for 2011 is 123.812. In a normal year (using 1981-2010 normals), ACE is 104. So certainly above average.

Wikipedia has a nice entry on ACE (and from what I've been able to gather in my experience in the field, most major meteorological articles on Wiki are maintained by actual experts on the subject...still I can't guarantee that the criteria used in this article is identical to that used by Dr. Maue. But a quick inspection shows it to be fairly close).

So let's quickly compare 2011 to other seasons. We know that 2005 is the benchmark of hurricane seasons. The ACE that year was an insane 248! So we're only 125 ACE points behind that in 2011. With that in mind, let's look at some other 17-21 storm seasons.

2011 (19 named storms): 124
1995 (19): 228
2010 (19): 165
1969 (18): 158

So only a few examples, but from that, you can see that 2011 is a classic example of quantity vs. quality...we had a heck of a lot of storms, but for the most part, they weren't the big ones.

I'll close out with a compendium of links about the tropics from the last few days....

2011 continued the streak of the United States' (mostly) good luck, in that a major, category 3 or stronger hurricane has not made landfall in the US since 2005....the longest such streak between majors in recorded history.

Here's an article from Sarasota, FL touting the "good luck" Florida has had the last several years. It includes comments from a number of meteorologists, including Dr. Phil Klotzbach of Colorado State, who spearheads the annual CSU Atlantic hurricane outlooks we've come to look to for guidance each hurricane season.

A quick blurb from Miami about how the Hurricane Center's goal of experimenting with 6 and 7 day forecasts for storms failed to materialize this season but should begin next season.

On the flip side, a new version of the COAMPS model being run by the Naval Research Lab in Monterey, CA showed substantial promise.

Lastly, Wx Underground's Dr. Jeff Masters has a comprehensive wrap-up of the 2011 hurricane season.