Hurricanes: A Roll of the Dice?

The Tropical Atlantic Ocean Basin    Source: NOAA

Although Danny became the Atlantic’s first major hurricane of 2015 yesterday, the last few seasons have been relatively quiet in the tropical Atlantic.  That’s not unusual as periods of above and below average activity in the tropics tend to vacillate back and forth.  An active season or two by itself doesn’t mean very much, just like a quiet season or two doesn’t indicate a trend.

For example, the period from 1995 through 2012 was a very busy time in the tropical Atlantic as all but two seasons saw an above average number of named storms.  In fact, during this 17 year period there was a seasonal average of 16 tropical storms and 8.5 hurricanes, of which 4 became “major” hurricanes – Category 3 or higher on the Saffir-Simpson Hurricane Intensity Scale.  That’s appreciably higher than the seasonal average of 10 tropical storms and 6 hurricanes, including 2 – 3 major ones.

Multiple catastrophic hurricanes did make landfall in the United States during this above average period – including hurricanes Charley and Ivan in 2004, Katrina and Wilma in 2005 and Ike in 2008.  The Mid-Atlantic Region also saw multiple land-falling tropical systems during this period, including hurricanes Fran, Floyd, Isabel and Irene.  One of the most destructive storms to affect the U.S. during this active 17-year period was Sandy in late October of 2012.  Sandy remains the second costliest natural disaster in U.S. history.

Conversely, as busy as this period was, the 17-year stretch prior to 1995 was just as quiet.  By comparison, there was a seasonal average of only 9.7 tropical storms and 5.3 hurricanes with 1.7 major hurricanes from 1977 through 1994.  However, there were still a few destructive hurricanes during this period, such as Gloria, Hugo and Andrew.  According to the National Hurricane Center, Hurricane Andrew had been the costliest natural disaster in U.S. history until Katrina in 2005.

Meanwhile, there were eight Category 5 hurricanes in just the five-year period from 2003 through 2007.  That helps illustrate that tropical storm and hurricane frequency and intensity are cyclical, and therefore, prone to busier and quieter stretches.  Although events like El Nino and La Nina can cause a seasonal fluctuation above or below average, they don’t cause prolonged stretches of above or below average tropical activity.

The Atlantic Ocean Basin (including the Gulf of Mexico and Caribbean Sea) has been quieter than average since 2013.  Luckily no major hurricane has made landfall in the U.S. since Wilma in 2005.  This week will mark the 10^th anniversary of Hurricane Katrina’s landfall in Louisiana.  That memory should help people realize just how damaging and deadly a hurricane or tropical storm could be.  That’s why listening to your favorite meteorologists for the latest weather forecasts and heeding the advice of local authorities when a storm threatens your region is crucial.