Getting More Active in the Tropics

NOAA recently updated its forecast for the 2020 Atlantic hurricane season.  They now expect a near record total of 19 – 25 tropical storms, of which 7 – 11 will become hurricanes and 3 – 6 of those will become major hurricanes.  There have already been nine tropical storms and two minimal hurricanes in 2020.  The ninth named tropical storm doesn’t normally develop until early October.  That fact, combined with how peak environmental conditions don’t normally develop until mid-to-late August, illustrates how far ahead of schedule the 2020 season is. 

Environmental conditions have generally been favorable for tropical development.  Some factors include warmer than average sea surface temperatures across much of the Atlantic Ocean (including the Gulf of Mexico and Caribbean Sea), below average amounts of vertical wind shear, and an above average West African monsoon.  As of July 9, NOAA’s Climate Prediction Center says there’s a 50%-55% chance that La Nina will develop during the fall.  That’s important since La Nina tends to promote more favorable conditions for development in the tropical Atlantic.

NOAA’s initial forecast when the season began June 1 still called for it to be above average with 13 – 19 tropical storms, 6 – 10 hurricanes and 3 – 6 hurricanes.  However, the fast start heading into the heart of the hurricane season helped lead them to revise their forecast upward.  The busiest Atlantic hurricane season occurred in 2005 with 28 tropical storms developed.  If NOAA’s revised forecast verifies, 2020 could become the second busiest Atlantic hurricane season on record (1933 is currently the second busiest Atlantic hurricane season on record with 20 tropical storms).  An “average” Atlantic hurricane season features 12 tropical storms, of which 6 becomes hurricanes with 3 “major” hurricanes (Category 3 or higher) based on 1981 – 2010 statistics.  

It’s important to remember, however, that a busier than average hurricane season doesn’t necessarily mean it will be a destructive or deadly season.  That’s because the bulk of storms that develop could remain at sea or weaken considerably before landfall.  Such was the case during the 2010 Atlantic hurricane season that tied for third busiest with 19 named storms.  That year, the United States didn’t experience any significant impacts from tropical systems.  On the other hand, the 2017 season tied for ninth busiest – in terms of total number of named storms – and became the most destructive Atlantic hurricane season on record with multiple catastrophic hurricanes like Harvey, Irma, and Maria.

Having a busier than average hurricane season would fit the recent pattern.  Nineteen of the last 25 Atlantic hurricane seasons have been busier than average.  Also, since 1995 the Atlantic Multidecadal Oscillation (AMO) has been in a warm phase.  That’s been a contributing factor because it helps more favorable conditions ensue with warmer sea surface temperatures in the tropical Atlantic.  While the National Hurricane Center expects the tropics to be largely quiet during the upcoming week, that isn’t expected to last.  When the next tropical storm develops in the Atlantic, it will be named “Josephine.”