Early Tropical Storms
Thanks to Dr. Jeff Masters for providing much of the following information. As of this writing (June 20,2013, p.m.,edt), Tropical Storm Barry is making landfall and dropping lots of rain on coastal areas of Veracruz state in Mexico. The storm is small and likely to bring heavy rainfall to only a small part of the Mexican coast. It is moving very slowly and could stay inland or turn towards the Gulf again. As we know from its name, Barry is the second storm of the Atlantic hurricane season, hardly a remarkable occurrence except that it’s still mid-June. Its formation date of June 19 is six weeks before the typical date of August 1. Whether this early occurrence date for the season’s second storm or the formation of two or more storms in June relates to global warming is a hard call, but such events often presage a busy hurricane season in the Atlantic and Caribbean.
Typically May and June are uneventful months storm-wise with an average of one June storm every two years over the 1870-2012 period, less so for May. However we still are in an active storm season phase which began in 1995 during which time June activity has doubled and May activity, although still very low, more than doubled. In 2007, there was both a May and a December storm!
Kossin (2008) concluded that there has been an increase in early-season and late-season storms that correlates with warming sea surface temperatures but uncertainties in this relationship are high.A larger data base from future years may clarify the relationship. Nevertheless, Kossin estimates that the length of hurricane seasons in the 1950-2007 period has increased by 5 to 10 days per decade. If the trend continues, we can expect more storms to follow tracks similar to the historical June pattern (see figure)-
forming quickly in the southern Gulf or Caribbean, staying south of the U.S. or in the western Gulf or, moving into the northern Gulf and affecting the Louisiana to Florida region. Regardless of location these early storms often generate heavy rainfall and flooding. In contrast, August and September storms, which tend to be more powerful, on average originate in the tropical Atlantic or eastern Caribbean, and may traverse the Gulf or run up the eastern seaboard. Barry seems unlikely to affect the U.S., but other June storms very well could.
Kossin, J.P 2008. Is the North Atlantic hurricane season getting longer? Geophysic. Res. Lett. vol. 35 ,L23705, doi:10.1029/2008GL036012
Masters, Jeff, 2013. http://www.wunderground.com/bog/JeffMasters/comment.html?entrynum=2444