Only Four Category 5 Hurricanes Have Made Landfall in the United States

Hurricane Andrew approaching south Florida in 1992  (Source: NOAA)

Since Hurricane Michael was officially upgraded to Category 5 status last month, it’s now one of an infamous group of only four Category 5’s to make landfall in the United States.  The previous three are: Hurricane Andrew in 1992, Hurricane Camille in 1969 and the unnamed Florida Keys hurricane of 1935.

Generally, the lower the air pressure, the stronger the hurricane is.  Standard sea level air pressure is approximately 1013 millibars.  Air pressure is considered a more accurate indicator of hurricane intensity than wind speed.  That’s because there is sometimes a lag in time between rising or falling air pressure and commensurate changes in the sustained wind speed of a hurricane.  For example, Hurricane Katrina reached its peak intensity as a Category 5 hurricane in 2005 over the open Gulf of Mexico with sustained winds of 175 mph and minimum air pressure of 902 millibars. 

Although it weakened to Category 3 intensity at its time of landfall with sustained winds of 125 mph, Katrina’s concurrent air pressure of 920 millibars was what you would expect in a much stronger hurricane.  By comparison, Hurricane Andrew had sustained winds of 165 mph and a slightly higher central air pressure of 922 millibars at landfall in south Florida in 1992.  The strongest winds in a hurricane can be found in the “eyewall” that surrounds the eye with the lowest air pressure in the hurricane’s center.

Hurricane Michael intensified up until it made landfall at peak intensity last October in the Florida panhandle with sustained winds of 160 mph and a minimum air pressure of 919 millibars.  It’s very unusual for a hurricane to intensify until it makes landfall.  There are two primary reasons for that.  Hurricanes rely on warm ocean water (typically at least 80° Fahrenheit) of sufficient depth to intensify or maintain strength.  As a hurricane approaches the coastline, the water is typically shallower and that can interrupt the delicate balance between the hurricane and its primary source of energy.  The interaction between the hurricane and a land mass that occurs prior to landfall also interrupts the circulation of the storm and can cause weakening, especially in a slow moving storm.   A hurricane doesn't have to be intense to be destructive and deadly as Hurricane Florence demonstrated last year.

Michael can be compared to another Florida hurricane that also intensified until it made landfall.  Hurricane Charley made landfall in August 2004 as a Category 4 hurricane with sustained winds of 150 mph.  Charley made landfall along the southwest coast of Florida and was the strongest hurricane to make landfall in the United States since Andrew in 1992.  The Gulf Coast and those inlands areas impacted by Hurricane Michael are still recovering as the start of the 2019 Atlantic hurricane season approaches on June 1.  The first named storm of the 2019 Atlantic hurricane season will be named “Andrea.”