A CLIMATOLOGY OF INTENSE (OR MAJOR) ATLANTIC HURRICANES

The variability of intense (or major) hurricanes in the Atlantic basin is investigated on both intraseasonal and interannual time scales. Di fferences are highlighted in characteristics between intense hurricane s and the weaker minor hurricanes and tropical storms. Intense hurrica nes show a much more peaked annual cycle than do weaker tropical cyclo nes. Ninety-five percent of all intense hurricane activity occurs duri ng August to October. In addition, over 80% of all intense hurricanes originate from African easterly waves, a much higher proportion than i s observed for weaker cyclones. Of all classes of Atlantic basin tropi cal cyclones, the intense hurricanes display the greatest year-to-year variability. The incidence of intense hurricanes also has decreased d uring the last two decades. A small portion of this decreased activity appears to be due to an overestimation of hurricane intensity during the period spanning the 1940s through the 1960s. After adjusting for t his bias, however, a substantial downward trend in intense hurricane a ctivity during recent years is still apparent. Given that intense hurr icanes are responsible for more than 70% of all destruction caused by tropical cyclones in the United States, an understanding is needed of the physical mechanisms for these observed variations of intense hurri cane activity.