How Active was the 2017 Atlantic Hurricane Season ?

2017 Atlantic Hurricane Season  (Source: NOAA)

The 2017 Atlantic hurricane season was historic.  A season with 17 tropical storms and 10 hurricanes (including 6 major hurricanes) would, ordinarily, be impressive all by itself.  But, the fact that three major hurricanes made landfall in the United States and its territories magnifies that many times over.

While some recent years (2010 – 2012) have seen more named tropical storms in the Atlantic Ocean than 2017, what made this season significant was the number of major hurricanes.  The six major hurricanes in 2017 plus the four that developed last year produced a total of 10 major Atlantic hurricanes.  That’s the highest two-year total since 2004-2005 (13).  

A “major” hurricane is defined as a Category 3 or higher on the Saffir-Simpson Scale.  NOAA implemented a minor change to the Saffir-Simpson Scale prior to the 2012 Atlantic hurricane season.  The old criteria for a Category 3 hurricane was sustained winds from 111 mph to 130 mph, while a Category 4 was 131 mph to 155 mph.  However, the new criteria makes a Category 3’s winds 111 mph to 129 mph and a Category 4’s winds 130 mph to 156 mph.  That slight difference was enough to make both Harvey and Irma Category 4 storms at their respective times of landfall.  Both had sustained winds of 130 mph when they made landfall in the United States.  

Had this change not been made to the Saffir-Simpson Scale, then the 2017 season would have had only two landfalling Category 3 hurricanes and one Category 4 (Maria).  The fact remains, though, that 2017 not only saw an abrupt end to the 12-year streak without a major hurricane landfall in the United States, but also became the first season with three landfalling Category 4 hurricanes.

This season also produced two Category 5 hurricanes in the Atlantic Ocean: Irma and Maria.  Irma set a record for the strongest Atlantic hurricane to develop outside the Gulf of Mexico or Caribbean Sea with peak winds of 185 mph and a minimum central air pressure of 914 millibars (mb).  Maria’s minimum central air pressure was even lower (908 mb), which made it the tenth strongest hurricane overall on record in the Atlantic Ocean.  Meteorologists consider air pressure to be a more accurate measure of hurricane intensity than wind speed.  The lower the air pressure is, then the stronger the hurricane tends to be.