In a typical year, if there is such a thing in nature, some 110 tropical cyclones are generated worldwide as a result of the combined activity of cyclogenesis in eight major ocean basins. Roughly 60% of all annual tropical cyclone activity is generated in the northern hemisphere, while the other 40% takes place in the southern confines of the Pacific and the Indian oceans. By and large the south Atlantic sees no tropical cyclones, except for a couple of rare instances in recent years including one in 2010.
Several factors affect cyclogenesis in the various basins; “El Nino Southern Oscillation” or ENSO in the eastern Pacific south of the equator, and whether there is an El Nino o La Nina , has been directly linked to cyclogenesis in the larger Atlantic basin. The Julian-Madden oscillation and the North Atlantic Oscillation are other factors that affect annual tropical cyclone activity. In addition, “pulses” of disturbed weather moving westward over the central Indian Ocean create an assembly-line of storms and tropical waves over equatorial Africa, which regularly emerge over the eastern Atlantic in the region south of the Cape Verde Islands to hitch a ride on the ocean corridor known as “hurricane alley” where many Atlantic hurricanes are generated.
While the year 2010 is not over yet, there have only been 86 tropical cyclones worldwide since 1 January 2010 and currently there is only one area, near southwestern Australia, which shows some potential for tropical cyclone development. Based on current atmospheric conditions it appears doubtful that there will be any significantly increased cyclogenesis in the southern hemisphere in what remains of 2010. By contrast, there were a total of 123 tropical cyclones worldwide in 2004, 129 in 2005, 112 in 2006, 103 in 2007, 112 in 2008 and 99 in 2009. Should the total number of tropical cyclones for 2010 stay at 86, this would be 23.9% below the average total number for the previous six years.
What is the significance of this sizeable reduction in the total number of tropical cyclones worldwide in 2010? This is an important question, especially in light of the ongoing debate about linking tropical cyclone activity to global warming and global climate change. Further analysis of the specifics of the 2010 season is needed, especially regarding the number of major hurricanes both in absolute numbers and as a percentage of the annual total. The role of the various external factors, such as various oscillations, that may have been at play in 2010 also needs analysis.
Of relevance to us in Florida, and the Gulf and Atlantic coastal regions of the United States, is the fact that the 2010 Atlantic Hurricane season was quite active with a total of 21 tropical cyclones generated in the basin north of the equator, compared to 9 in 2009, 16 in 2008 and 17 in 2007. The fact that there was an ongoing La Nina event off the Pacific coast of Peru is considered a contributing factor to this level of tropical cyclone activity in the Atlantic in 2010. Despite this heightened activity in the Atlantic the USA and especially Florida emerged basically unscathed, although Texas, the Carolinas and the mid-Atlantic and northeastern states suffered some glancing blows, without enduring actual landfalls, from storms in the Gulf and the northwestern Atlantic. By contrast the Caribbean, Central America, Mexico and Bermuda were hit several times during the season.
Tropical Storm OMEKA is Active!
As it often happens, just to challenge my comments above, earlier today 20 December 2010 tropical storm OMEKA is on the move to the south by southeast of the Midway Islands in the central-western Pacific ocean moving toward the northeast. The storm is far away from islands that are few and far between in that vast expanse of ocean, so the main threat that it poses is to navigation.
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