2017 Hurricane Season Breaks Records

Hurricane Maria's forecast track   Source: NOAA

September is typically the busiest month of the hurricane season for the Atlantic Ocean Basin, which includes the Gulf of Mexico and Caribbean Sea.  This season has been no exception with an historic stretch of devastating hurricanes over the last few weeks. 

There have been two Category 5 hurricanes in the Atlantic Ocean (Irma, Maria) for only the sixth time in recorded history and first time since 2007 (Dean, Felix).  The record for most Category 5 hurricanes during an Atlantic hurricane season (June 1 – November 30) is 4 (Emily, Katrina, Rita, Wilma) in 2005.  One Category 5 hurricane is rare enough, but more than one is exceptionally rare.  For example, prior to 2005, the last time at least two Category 5 hurricanes occurred during the same season was in 1961 (Carla, Hattie). 

It’s interesting to note that before weather satellites began being used in the 1960s, it was very difficult to determine if a tropical storm or hurricane existed if it remained over the open ocean.  There could have been additional seasons with Category 5 hurricanes, but there was no reliable way to know they were there.  Not only were there no weather satellites during the 1932 and 1933 hurricanes seasons (when there were also two Category 5 hurricanes) but that was also before they were named.

Hurricane Irma broke multiple records during its 75 hours as a Category 5 hurricane over four days (September 5 – 9).  It had the highest sustained winds (185 mph) of any Atlantic hurricane outside of the Gulf of Mexico or Caribbean Sea.  In fact, Irma’s peak winds of 185 mph tie it with Gilbert, Wilma and the unnamed 1935 Florida Keys hurricane as second highest on record behind only Hurricane Allen (190 mph) in 1980.  Moreover, Irma’s 75 hours at Category 5 intensity also ranks as the second highest length of time at Category 5 intensity, narrowly behind the 78 hours a November 1932 hurricane in the Caribbean Sea.

At peak intensity, Maria was slightly more intense than Irma.  Although Maria’s maximum sustained winds were 175 mph, its minimum central air pressure was 908 millibars (mb).  Scientists consider air pressure to be a more accurate measure of hurricane intensity than wind speed.  That’s because lag time can exist in between changes in the air pressure and wind speed of strengthening or weakening hurricanes.  On account of pressure, Hurricane Maria ranks as the tenth strongest hurricane on record in the Atlantic Ocean.  Maria’s lowest air pressure (908 mb) was not only lower than Irma’s (914 mb), but was the lowest observed pressure of any Atlantic hurricane since Category 5 Dean (905 mb) in 2007. 

2016-2017 are the first consecutive years since 2004-2005 to feature a Category 5 hurricane in the Atlantic Ocean, following last season’s Hurricane Matthew.  If the hurricane season were to end today with 13 tropical storms and 7 hurricanes, including 4 major ones, it would be a touch busier than the seasonal average of 12, 6 and 3.  However, hurricane season runs through November 30, so those totals can only increase.