The 2011 Atlantic hurricane season: another strangely active one

[phantom power]

Wednesday marks the final day of the 2011 Atlantic hurricane season, and it was another very odd year. The season featured a huge number of named storms--nineteen--tying 2011 with 2010, 1995, and 1887 as the 3rd busiest year for tropical storms. Only 2005 and 1933 had more named storms since record keeping began in 1851. However, 2011 had an unusually low percentage of its named storms reach hurricane strength.

The year started out with eight consecutive tropical storms that failed to reach hurricane strength--the first time on record the Atlantic has seen that many storms in row not reach hurricane strength. We had a near-average average number of hurricanes in 2011--seven--meaning that only 37% of this year's named storms made it to hurricane strength. Normally, 55 - 60% of all named storms intensify to hurricane strength in the Atlantic. There were three major hurricanes in 2011, which is one above average, and the total Accumulated Cyclone Energy (ACE)--a measure of the destructive potential of this season's storms--was about 20% above average.

The rare combination of near-record ocean temperatures but unusually dry, stable air over the Atlantic is no doubt at least partially responsible for 2011's unusually high count of named storms, but near-average number of hurricanes and ACE. Both 2010 and 2011 had nineteen named storms, making it the second busiest 2-year period in the Atlantic behind 2004 - 2005. Even when one considers that 2 - 4 tropical storms from both 2010 and 2011 would likely have been missed before the advent of satellites, the tropical storm activity of 2010 - 2011 is still very remarkable (in 2011, Tropical Storm Franklin, Tropical Storm Jose, and the unnamed 19th tropical storm of September 1 would probably have been missed before satellite technology came along, since they were all weak, short-lived storms that did not impact land or shipping.)

http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=1994

[Odin2005]

1. It was mostly tropical storms, fortunately.

It could have been a lot worse.