Some Perspective on Category 5 Hurricanes

Hurricane Wilma at peak intensity on 10/19/05  (Source: NOAA)

Hurricane Wilma became the strongest Atlantic hurricane on record on this date in 2005.  Although the sustained winds in 1980’s Hurricane Allen were slightly higher at peak intensity (190 mph vs. 185 mph), Wilma’s minimum central air pressure of 882 millibars set a new record for the Atlantic Ocean Basin.  The previous record was 888 millibars during Hurricane Gilbert in 1988.  Standard sea level pressure is approximately 1013 millibars.

Hurricane intensity is measured on the Saffir-Simpson scale with sustained winds in a Category 1 storm of 74 mph to 95 mph.  By comparison, Category 5 hurricanes feature sustained winds of 156 mph or greater.  Earlier this month, Hurricane Matthew reached Category 5 intensity with sustained winds of 160 mph.  According to the National Hurricane Center, Matthew was the first Category 5 hurricane in the Atlantic Ocean since Felix in 2007.

Following a record eight Category 5 hurricanes in a five year period in the Atlantic Ocean through 2007, some may have assumed that Category 5 storms are a relatively frequent occurrence.  However, that’s not the case since Category 5 hurricanes only form under specific circumstances.  There has been an approximate total of only 30 Category 5 hurricanes in the Atlantic Ocean (including the Gulf of Mexico and Caribbean Sea) since 1920.  The total is approximate because before there were weather satellites and radar, there was no reliable way to tell if a hurricane was over the open ocean unless a ship was nearby.

Of the 30 Category 5 hurricanes that have developed in the Atlantic, 17 occurred in September, 7 in August and 4 in October with 1 each in July and November.  Prior to Wilma, the last Atlantic Category 5 hurricane to occur in October was Mitch in 1998.  Like Wilma and Matthew, Hurricane Mitch also developed in the Caribbean Sea.  However, unlike Hurricanes Wilma and Mitch, Matthew wasn’t a Category 5 for very long.  Hurricane Matthew finished tied for shortest length of time (six hours) at Category 5 intensity among Atlantic hurricanes.

Hurricane Nicole was another major October hurricane that made landfall in Bermuda as a Category 3 hurricane last week.  At peak intensity, Nicole was a Category 4 hurricane with sustained winds of 130 mph.  According to Colorado State University scientist Dr. Philip Klotzbach, Hurricanes Matthew and Nicole were the first pair of Category 4 and 5 Atlantic hurricanes on record in the month of October.  Although three Category 5 hurricanes have made landfall in the United States, two were in August and the third was in early September.