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.

Weather Quiz

Hurricane Danny is east of the Caribbean Islands    Source: NOAA

True or False.

Upgraded to a hurricane this morning, Danny, is the first “major” (Category 3 or higher) hurricane of 2015 in the Atlantic Ocean.

---

Answer to Weather Quiz question from August 6.

C.  Andrew.  Although, Katrina, Rita and Isabel were all Category 5 hurricanes, they were only at this intensity while over the open sea and each weakened before making landfall.  This Monday (August 24) is the 23^rd anniversary of when Andrew became only the third Category 5 hurricane on record to make landfall in the United States.

Does El Nino impact Atlantic Ocean Hurricanes?

Hurricane Gonzalo, October 2014  Source: NASA

If you’re one of those people thinking this year’s hurricane season has been quiet, than you would be correct.  Although a tropical storm developed in May (Ana) – before the season officially began – it has been a relatively quiet season.  In fact, NOAA recently issued the August update to its seasonal hurricane forecast and concluded the 2015 hurricane season should remain quieter than average. 

That’s largely because of the developing El Nino event that is characterized by warmer sea surface temperatures in the central and eastern equatorial Pacific Ocean.  This situation affects global weather patterns and helps make conditions more favorable for tropical storm formation off the west coast of Mexico.  However, El Nino also tends to make conditions in the tropical Atlantic Ocean less favorable for tropical storms.

NOAA’s early August update for the 2015 Atlantic hurricane season predicts a total of 6 to 10 tropical storms, of which 1 to 4 will become hurricanes with up to one “major” hurricane – Category 3 or higher on the Saffir-Simpson Hurricane Intensity Scale.  So far this season, there have been only three short-lived tropical storms.  No hurricanes have developed anywhere in the Atlantic Ocean Basin (that includes the Caribbean Sea and Gulf of Mexico) since Gonzalo last October.

People tend to forget that a quieter than average hurricane season doesn’t necessarily mean that it can’t or won’t feature a high impact storm.  For example, the 1992 season was quieter than average (concurrent with a moderate El Nino event) and featured only 7 tropical storms, 4 hurricanes and 1 major hurricane.  However, many will remember that “major” storm as Hurricane Andrew.  In fact, Andrew was named as a tropical storm on this date 23 years ago and went on to become only the third Category 5 hurricane on record to make landfall in the United States.

Although the busiest part of the hurricane season is just getting underway (with September averaging the highest number of tropical storms and hurricanes), every expectation is for this season to finish up being the third consecutive quieter than average one.  Meteorologists at the National Hurricane Center will track any developments in the tropics while my colleagues and I on the WUSA9 weather team will continue to monitor any tropical storms that form should they track toward the U.S. East Coast.