A Closer Look at Category 5 Hurricanes

 

Hurricane Lorenzo, September 2019 (Source: NOAA)

Although the Atlantic hurricane season doesn’t officially get underway until June 1, the upcoming season has already become a topic of conversation.  That’s because Colorado State University recently issued its forecast for the upcoming season.  NOAA will release its seasonal forecast in the coming weeks.  The last several years have featured busier than average Atlantic hurricane seasons.  Four of the last six seasons have also produced at least one Category 5 hurricane.

A Category 5 hurricane on the Saffir-Simpson Hurricane Wind Scale has sustained winds around the center of circulation, or “the eye,” of at least 157 mph.  They require ideal conditions to form including very warm ocean water (at least 80° Fahrenheit) to a sufficient depth (200’ or greater) and a lack of wind shear (winds that change direction with altitude).  It’s rather rare for a hurricane to have ideal conditions for intensification over the open ocean for long enough to reach Category 5 status.

Category 5 hurricanes are so rare that only 37 have formed since 1920, or between 3 and 4 per decade.  However, what’s more important than the overall number of Category 5 hurricanes that develop is where they track.  Only four Category 5 hurricanes have made landfall in the United States, most recently Michael in 2018.

The last two decades have been quite active in the tropical Atlantic.  Both in terms of the overall number of tropical storms and hurricanes that developed, but in the number of Category 5 hurricanes as well.  Starting with Isabel in 2003, a total of 14 Category 5 Atlantic hurricanes have developed.  More Category 5 Atlantic hurricanes have developed in the last 19 years, than in the preceding 43 years dating back 1960 (13).  Hurricane seasons are cyclical by nature with some that are busier than others due to factors such as ENSO status (the presence of El Nino or La Nina) and sea-surface temperature (SST) anomalies.

There have been quieter than average hurricane seasons that have seen a Category 5 hurricane, such as Andrew in 1992.  There have been several seasons that have featured multiple Category 5 hurricanes, such as 2005 and 2017.  Some busier than average Atlantic hurricane seasons with multiple Category 5 storms also occurred long ago such as 1932 and 1933.  They have just been more frequent in recent decades.  Four Category 5 hurricanes developed in 2005 alone, with another 6 between 2016 and 2019.  The last Category 5 Atlantic hurricane was Lorenzo in September 2019.