Some Hurricane Perspective

Hurricane Harvey in August 2017  (Source: NASA)

Hurricane intensity is measured on the Saffir-Simpson Scale.  A tropical storm becomes a Category 1 hurricane when sustained winds reach 74 mph around the center of the storm.  A hurricane becomes “major” when it reaches Category 3 intensity with sustained winds of 111/+ mph.  Category 4 and 5 hurricanes are more intense and much rarer.

The period from 1995 through 2012 saw an uptick in the number of tropical storms and hurricanes in the Atlantic Ocean with 15 of the 17 hurricane seasons busier than average.  Despite that busier than average cycle in the tropical Atlantic, no major hurricane made landfall in the United States from October 2005 until August 2017. 

After Hurricane Wilma made landfall in Florida in October 2005, no hurricane of any intensity made landfall in Florida until minimal Hurricane Hermine in September 2016.  Hermine was also significant for being the first hurricane in the Gulf of Mexico in more than 1,000 days.  Last August, Hurricane Harvey became the first “major” hurricane to make landfall in the United States since Wilma nearly 12 years earlier.  That set a new record for length of time between landfalling major hurricanes in the United States.

Harvey, Irma and Maria each made landfall in the United States or one of its territories last year as Category 4 hurricanes.  Irma and Maria each reached Category 5 intensity, but weakened slightly before making landfall.  However, Irma was a Category 5 with sustained winds of 185 mph when it made landfall in the U.S. Virgin Islands and caused catastrophic damage.  There were wind gusts of more than 200 mph during Irma on the Virgin Islands, according to the National Hurricane Center. 

Category 5 hurricanes are the rarest of storms, only occurring under very specific circumstances.  In 2005, Wilma became the strongest hurricane on record in the Atlantic Ocean Basin with maximum sustained winds of 185 mph and a minimum central air pressure of 882 millibars (standard sea level pressure is 1013.25 mb).  Air pressure is considered a more accurate measure of hurricane intensity than wind speed.  However, in October 2015, Hurricane Patricia became the strongest on record in the Western Hemisphere with sustained winds of 215 mph and a minimum central air pressure of 872 mb.  Patricia developed in the eastern Pacific near the west coast of Mexico and had the highest sustained winds of any hurricane on record.