Decadal Trends of Atlantic Basin Tropical Cyclones (1950-1999)

Ten-year moving averages of the seasonal rates for "named storms", tropical storms, hurricanes, and major (or intense) hurricanes in the Atlantic basin suggest that the present epoch is one of enhanced activity, marked by seasonal rates typically equal to or above respective long-term median rates. As an example, the 10-yr moving average of the seasonal rates for named storms is now higher than for any previous year over the past 50 yr, measuring 10.65 in 1994, or 2.65 units higher than its median rate of 8. Also, the 10-yr moving average for tropical storms has more than doubled, from 2.15 in 1955 to 4.60 in 1992, with 16 of the past 20 yr having a seasonal rate of 3 or more (the median rate). For hurricanes and major hurricanes, their respective 10-yr moving averages turned upward, rising above long-term median rates (5.5 and 2, respectively) in 1992, a response to the abrupt increase in seasonal rates that occurred in 1995. Taken together, the outlook for future hurricane seasons is for all categories of Atlantic basin tropical cyclones to have seasonal rates at levels equal to or above long-term median rates, especially during non-El Nino-related seasons. Only during El Nino-related seasons does it appear likely that seasonal rates might be slightly diminished.