• Hurricanes;
  • tropical cyclones

[1] An analysis of Atlantic hurricane data (HURDAT), using a hurricane activity index that integrates over hurricane numbers, durations, and strengths during the years 1851–2007, suggests a quasi-periodic behavior with a period around 60 years superimposed upon a linearly increasing background. The linearly increasing background is significantly reduced or removed when various corrections were applied for hurricane undercounting in the early portion of the record. The periodic-like behavior is persistent in uncorrected HURDAT data as well as in data corrected for possible missing storms. The record contains two complete cycles: 1860–1920 and 1920–1980. The 2004 and 2005 hurricane seasons were unusual in that two intense hurricane seasons occurred in consecutive years. The probability for this happening in any given year is estimated to be less then 1%. Comparing the last 28 years (1980–2007) with the preceding 28 years (1953–1980), we find a modest increase in the number of minor hurricanes (category 1 and 2); however, we find no increase in the number of major hurricanes (category 3–5). The hurricane activity index is found to be highly correlated with the Atlantic Multidecadal Mode (AMM). If there is an increase in hurricane activity connected to a greenhouse gas induced global warming, it is currently obscured by the 60 year quasi-periodic cycle.