Rating Hurricanes: The Saffir-Simpson Scale

Hurricanes Maria and Irma both maxing out at Category 5 strength during the same year is a rare event for the Atlantic basin, something that last occurred a decade ago, and has only happened a few other times in historical records.

Atlantic Category 5 hurricanes are scarce overall, with only 33 known to exist dating to 1924, according to NOAA. Two hurricanes attaining this highest level of intensity in a single year is an exceptional event and something that has only been documented five other times.

The 2007 season was the last time a pair of Category 5 hurricanes roamed the Atlantic in the same year with Hurricanes Dean and Felix both making landfall at that intensity in Mexico and Nicaragua, respectively.

The other years with more than one Category 5 hurricane in the Atlantic are 1932, 1933, 1961 and 2005.

(HURRICANE CENTRAL: Full Coverage on Maria)

The 2005 season had the most Category 5 hurricanes of any season on record with four total: Emily, Katrina, Rita and Wilma.

A nearly perfect atmospheric and oceanic environment is needed for hurricanes to grow into Category 5 monsters.

Low wind shear, high moisture content in the atmosphere and abundant oceanic heat content are just some of the conditions that must exist in tandem with each other for a tropical low-pressure system to grow into a Category 5 hurricane. Other factors are in play as well, including a lack of land interaction and the internal structure of the growing hurricane itself.

Irma and Maria were both able to tap into a ripe environment that includes the variables mentioned above for rapid strengthening into Category 5 hurricanes in a roughly two-week period. Unfortunately, this rapid intensification has also occurred at a time when several northeast Caribbean Islands have been in the crosshairs of its devastating eyewall impacts.