The Atlantic hurricane season is getting longer [View all]

[phantom power]

Andrea's formation in June continues a pattern of an unusually large number of early-season Atlantic named storms we've seen in recent years. Climatologically, June is the second quietest month of the Atlantic hurricane season, behind November. During the period 1870 - 2012, we averaged one named storm every two years in June, and 0.7 named storms per year during May and June. In the nineteen years since the current active hurricane period began in 1995, there have been fifteen June named storms (if we include 2013's Tropical Storm Andrea.)

June activity has nearly doubled since 1995, and May activity has more than doubled (there were seventeen May storms in the 75-year period 1870 - 1994, compared to 6 in the 19-year period 1995 - 2013.) Some of this difference can be attributed to observation gaps, due to the lack of satellite data before 1966. However, even during the satellite era, we have seen an increase in both early season (May - June) and late season (November - December) Atlantic tropical storms.

Dr. Jim Kossin of the University of Wisconsin looked at the reasons for this in a 2008 paper titled, "Is the North Atlantic hurricane season getting longer?" He concluded that there is a "apparent tendency toward more common early- and late-season storms that correlates with warming Sea Surface Temperature but the uncertainty in these relationships is high." He found that hurricane season for both the period 1950-2007 and 1980-2007 got longer by 5 to 10 days per decade (see my blog post on the paper.)

http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=2431