2019 Hurricane Season Outlook

This past week Colorado State University released its April outlook for the upcoming Atlantic hurricane season.  Led by scientist Dr. Philip Klotzbach, the forecast calls for a slightly below average 2019 season with 13 tropical storms, of which 5 will intensify into hurricanes, including 2 major hurricanes.  An “average” Atlantic hurricane season has 12 tropical storms, 6 hurricanes and 3 major hurricanes (based on averages from 1981 – 2010).

Two primary factors in the below average hurricane outlook for 2019 are the presence of weak El Nino conditions and below average sea surface temperatures in the tropical Atlantic.  One of the byproducts of El Nino is an increased amount of wind shear (differing wind speeds with altitude) that tends to preclude tropical development.  NOAA expects weak El Nino conditions to continue into the summer.  Tropical storms and hurricanes also rely on warm ocean water, typically at least 80° Fahrenheit, to a sufficient depth (usually 200’ or greater) as its energy source, so cooler than average water is not ideal.   

A tropical disturbance becomes a tropical storm when sustained winds around the center reach at least 39 mph.  That’s also when a system gets a name.  A tropical storm becomes a hurricane when sustained winds reach 74 mph.  A hurricane becomes “major” when sustained winds reach 111 mph and that makes it a Category 3 on the Saffir-Simpson Scale.  It’s important not to focus too much on the intensity or “Category” of a hurricane, since they are all capable of being destructive and deadly.  The remnants of Harvey in 2017 and Florence in 2018 both continued to cause devastating flooding in areas well-inland once they were no longer hurricanes.  Tropical storms are also capable of producing widespread and deadly flooding such as during Allison in 2001.  

Tropical storms and hurricanes are warm-core systems that rely on warm ocean water for their energy.  That’s unlike mid-latitude cyclones that rely on differences in temperature to intensify.  Consequently, another key difference between tropical and non-tropical storms is that the strongest winds are concentrated around the center of a tropical storm or hurricane, while the highest winds of a non-tropical mid-latitude storm (like a Nor’Easter), cover a much larger geographic area often considerable distances from the center of the storm.  

Whether or not a hurricane season is busier than average is less important than where the tropical storms and hurricanes track.  For example, the 1992 Atlantic hurricane season was quiet with only one major hurricane.  However, the one major hurricane was Andrew, which remains one of the costliest natural disasters in U.S. history.  While the 2013 – 2015 Atlantic hurricane seasons were quieter than average, the subsequent three seasons through 2018 were each busier than average with a number of destructive and deadly storms.  

The World Meteorological Organization met recently and officially retired the names “Florence” and “Michael” since they were destructive and deadly.  When the 2018 list of hurricane names is used again in 2024, those names were replaced with “Francine” and “Milton.”  Hurricane season begins on June 1 and the first named storm of 2019 will be named “Andrea.”