2011 Hurricane Season Is Over

2011 Hurricane Season is over. This season was active in the term of number of storms. However, the number of them becoming hurricane was rather low due to the lack of instability in the upper atmosphere. However, the number of major hurricane was within the norm. Two storms made landfall on America, Don and Irene. Irene was the first hurricane to hit America since Ike in 2008. It was forecasted to be the “Big One” for the East Coast from Carolinas to New York. As it turned out, the storm surge was not bad for New York. However, Irene was a huge flood event for New England, so it was the “Big One” in terms of flooding.

So, how does 2011 stack up? All mean, medians, and standard deviation is from 1870 to 2010. Statistical value has changed because there have been changes made for the past seasons.

19 Storms
Mean = 9.34 (9)
Median = 9
Standard Deviation = 3.98 (4)

It is an above average season with 19 storms. A season with 13 or more storms is above average. In fact, 2011 ties with 1995 and 2010 Hurricane Season. How often do we have season with back to back with 19 storms? 19 storms is an outlier, which is a rarity. Only 2005 (28) and 1933 (21) had more.

7 Hurricanes
Mean = 5.43 (5)
Median = 5
Standard Deviation = 2.61 (3)

The number of hurricanes is within average. A season with 8 or more hurricanes is above average. 2005 had the most hurricanes in one season at 15.

3 Major Hurricanes
Mean = 2.07 (2)
Median = 2
Standard Deviation = 1.75 (2)

The number of major hurricanes is within average. A season with 4 or more major hurricane is above average. This time, 1950 had the most major hurricanes on record with 8. However, re-analysis show that 1950 may not have had 8 major hurricanes, but instead 6 major hurricanes. So, 2005 would be the winner with 7 major hurricanes.

119 Accumulated Cyclone Energy (ACE)
Mean = 91.62 (92)
Standard Deviation = 54.30 (54)
Median = 83

The ACE is within average. A season with an ACE of +54 above standard deviation or 146 or above is considered active. The season with the most ACE is 2005 at 248.

6.3 ACE/Storm
Mean = 9.74 (9.7)
Median = 9.1
Standard Deviation = 4.18 (4.2)

The ACE/Storm is within average. Anything above the standard deviation of 4.2 for the mean or 13.9 is considered above average. The season with the highest ACE/Storm is 1915 at 21.2, but that is before satellites. The season with the highest ACE/Storm in the satellite era is 1961 at 18.6 ACE/Storm. 1961 was the year Hurricane Carla made landfall on Texas. For kicks, the ACE/Storm for 2005 was within average of 8.9.

36.8 Percent Of Storms Became Hurricanes
Mean= 58%
Median = 58%
Standard Deviation = 17%

The percentage of storms that became hurricane is below average. This is despite the fact that 19 storms formed in 2011. In fact, it is more than 17% (standard deviation) below the mean. This would show that the lack of vertical instability was a huge factor. The season with the highest percentage of storms becoming hurricane is 1884 at 100%, but this is before satellite were used. The season with the highest percentage of storms becoming hurricane is 1977 at 83%. Interesting fact about 1977, it was quiet in the Atlantic, East Pacific, and West Pacific. It comes to show that even active seasons do not have high percentage of storms becoming hurricane, like 2005, which was 54% of storms became hurricanes.

15.8 Percent Of Storms Became Major Hurricanes
Mean = 21%
Median = 20%
Standard Deviation = 15%

The percentage of storms becoming major hurricane is within average. This is rather strange for a season where a low percentage of storms becoming hurricanes. All in all, the 2011 Hurricane Season was active despite the low percentage of hurricanes and lack of vertical instability. The season with the highest percentage of storms becoming major hurricane is 1930 at 67%, but this is before satellite were used. The season with the highest percentage of storms becoming major hurricane is 1961 at 64%. In the active 2005 season, only 25% of storms became major hurricanes and that is within average.

What does the 2012 Hurricane Season be like? It will be hard to say at this time since it does not start until June 1, 2012. Usually, when there are two back to back season that are active, the next season is usually less active. Right now, we are in a La Nina and usually by the spring and summer, it is Neutral. Rarely, a year can go from La Nina to El Nino. The last time that happened was in 2009, in which the season was quiet. Here are the years that went from La Nina to El Nino.
1904
1911
1918
1925
1939
1951
1968
1976
2006
2009

If 2012 does not see an El Nino and stays Neutral, we can be in it for another active season. 2003 to 2005 had three active back to back seasons. 2005 was the most active on record with 28 storms. It was the year Hurricane Katrina ravaged the Gulf Coast. I would not rule out 2012 being active like 2010 and 2011. I should have a much better idea by Spring of 2012. So stay tuned.

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