A Busy Atlantic Hurricane Season ?

Where Tropical Cyclones Develop Globally  (Source: NASA)

NOAA just issued its forecast for the upcoming Atlantic hurricane season that officially gets underway on June 1 and runs through November 30.  NOAA is expecting a busier than average season with 13 – 19 tropical storms, of which 6 – 10 become hurricanes including 3 – 6 major hurricanes.  Colorado State University’s April forecast was very similar to NOAA’s and called for 16 tropical storms, 8 hurricanes and 4 major hurricanes.  

An average season has 12 tropical storms, 6 hurricanes and 3 major hurricanes.  A “major” hurricane is a Category 3 or higher on the Saffir-Simpson Hurricane Wind Scale with sustained winds of at least 111 mph.  A primary factor in NOAA’s forecast for an above average season is the fact no El Nino or La Nina is currently present.  While El Nino conditions contribute to less favorable conditions for tropical development in the Atlantic Ocean Basin, La Nina conditions help create a more favorable environment.  

As the summer wears on, La Nina conditions could develop and that would create the potential for an even busier Atlantic hurricane season.  La Nina conditions are characterized by a decrease in the amount of wind shear (winds of differing speeds with altitude) and warmer sea surface temperatures in the tropical Atlantic.  Many of the busiest Atlantic hurricane seasons have been during moderate to strong episodes of La Nina, such as the 1995 and 2010 seasons.  By comparison, during moderate to strong episodes of El Nino the tropical Atlantic is often quieter such as during the 1992 and 2015 seasons.  

However, the overall number of tropical storms and hurricanes that develop is less important than where they track.  An otherwise quiet season could be very destructive and deadly.  For example, the 1992 Atlantic season was relatively quiet with only 7 tropical storms, 4 hurricanes and 1 major hurricane.  But that hurricane was Andrew, which made landfall in southern Florida near the town of Homestead as a Category 5.  It was the costliest natural disaster in U.S. history at the time and remains one of the costliest hurricanes on record.  On the other hand, the 2010 season was an active one with 19 tropical storms, 12 hurricanes and 5 major hurricanes, but none had significant impacts in the United States.

Although the first named 2020 storm, Arthur, has already come and gone, having a named storm prior to the official start of hurricane season doesn’t guarantee an active one.  2020 is the sixth consecutive season at least one named storm formed prior to June 1.  If the forecasts for the upcoming season are correct and it is busier than average, then 2020 would be the fifth consecutive busier than average season.  The last time five or more consecutive seasons were busier than average was an eight year stretch from 1998 – 2005.  The next named storm to develop in the Atlantic Ocean Basin will be “Bertha.”