Atlantic tropical cyclone energy well below normal

There have been ten named storms so far this hurricane season. Since the normal amount of named storms for a full season is 12, one could assume that 2013 is on the way to being an above normal hurricane season. However, most of the storms have been weak, and there have only been two hurricanes. Another measure of hurricane activity is the Accumulated Cyclone Energy (ACE) index. This index takes into account the strength and lifespan of the storm.

As you can see in the table below, through September 21 the North Atlantic basin, which includes the Gulf of Mexico, is running well below normal this year. The Northern Hemisphere is also well below normal, even with powerful Super Typhoon Usagi wreaking havoc in the Western Pacific. Since 1950, only 6 years have had a lower ACE index than 2013 in the North Atlantic.

Basin   Current YTD   Normal YTD % of Normal YTD Yearly Climo*
  Northern Hemisphere   169.6875   366 46% 562
  Western N Pacific   87.99   178 49% 302
  Central N Pacific   6.31      
  Eastern N Pacific   53.265   108 49% 138
  North Atlantic   23.055   72 32% 104
  North Indian   5.3775   7 76% 18
  Southern Hemisphere +   191.827   209 91% 209
  Global++   293.9825   539 54% 771

*Climatology from historical 1981-2010 Tropical cyclone best track datasets
+Southern Hemisphere year to date is the seasonal value from October – Current due to offset nature of SH TC season
++Year to Date Values are Calendar year for Northern Hemisphere Basins

Only six years since 1950 have had lower ACE than 2013 through September 22
Only six years since 1950 have had lower ACE than 2013 through September 22

Data from


Fred Campagna

President and Chief Meteorologist - Right Weather LLC AMS Certified Consulting Meteorologist #756 AMS Certified Broadcast Meteorologist #126

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