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12.09.2019

Colorado State University Researchers Analyze Slightly Above-Average 2019 Atlantic Basin Hurricane Season

Dr. Phil Klotzbach - Colorado State University, Department of Atmospheric Science

Researchers at Colorado State University have recently conducted an analysis of the slightly above-average 2019 Atlantic basin hurricane season.  The CSU Tropical Meteorology Project team accurately predicted 2019 Atlantic hurricane numbers, but under-predicted named storm activity.  The Atlantic hurricane season extends from June 1 – November 30. 

The 2019 Atlantic basin hurricane season was well above-average for the number of named storms and near-normal for the number of hurricanes and major hurricanes; those defined as Category 3+ on the Saffir-Simpson Hurricane Wind Scale.  The season was very active from a named storm perspective with a total of 18 named storms, as compared with the 1981-2010 seasonal average of 12.  In 2019, seven of the named storms that formed lasted one day or less, which is the most Atlantic storms of such short duration on record.  Additionally in 2019, there were six hurricanes and three major hurricanes, which is the same as the 1981-2010 average values for these quantities.

Various climate factors contributed to a more active 2019 season than anticipated in CSU’s first annual forecast issued in April 2019.  The initial forecast was based on the assessment that a weak El Niño - slightly warmer than normal waters in the tropical Pacific - would persist through the Atlantic hurricane season.  Yet, El Niño actually faded during the early summer months likely creating vertical wind shear conditions that were more favorable for storm formation, thereby necessitating slight increases in seasonal forecast updates issued in early June, early July and again in early August.  Sea surface temperatures in the tropical Atlantic were also slightly warmer than normal during the peak of the season from August-October, in essence, providing more fuel for developing cyclones.  Warmer sea surface temperatures also tend to be associated with lower pressure and a more unstable atmosphere, both of which favor hurricane development.   

The most notable storm of the 2019 season was Hurricane Dorian which devastated the northwestern Bahamas before impacting the southeast United States as well as the Atlantic Provinces of Canada.  With a maximum lifetime wind intensity of 160 knots, Hurricane Dorian was the most intense Atlantic hurricane outside of the tropics on record and was also the strongest hurricane on record to make landfall in the Bahamas.  Hurricane Dorian was an extremely powerful storm that pummeled the Abaco Islands and Grand Bahama Island on September 1st and 2nd at Category 5 intensity before making landfall near Cape Hatteras, North Carolina in the U.S. as a Category 1 hurricane.

Hurricane Dorian insured loss estimates from catastrophe risk modeling firms for the Caribbean (primarily the Bahamas) range between $1.5 billion to $3 billion by AIR Worldwide and between $3.5 billion to $6.5 billion according to RMS.  Estimates reflect losses associated with wind-related property damage, storm surge-driven coastal flooding and business interruption for island commercial establishments and resort properties.   Insured losses do not include overall anticipated economic losses, particularly in the Caribbean that has a lower rate of insurance coverage than in the U.S.  Insured losses in the U.S. have been estimated to range from $500 million to $1.5 billion, inclusive of losses to the National Flood Insurance Program (NFIP). 

Other notable storms of 2019 include Hurricane Lorenzo. In late September, Lorenzo became the farthest east Atlantic Category 5 hurricane formation on record (breaking the old record set by Hurricane Hugo in 1989).  Lorenzo would then go on to impact the Azores, Ireland and the UK. 

While only a tropical storm for 45 minutes before making landfall in southeast Texas, Tropical Storm Imelda tracked very slowly after making landfall in southeast Texas in mid-September, dumping copious amounts of rainfall.  The associated flooding resulted in damages of ~$2 billion, per estimates from Aon.    

CSU’s Tropical Meteorology Project has been issuing forecasts for the past 36 years.  A brief qualitative outlook for the 2020 hurricane season will be issued on December 12th, with the first full seasonal outlook to be released on April 2nd. 

The CSU Tropical Meteorology Project verification report for 2019 can be accessed in full at: tropical.colostate.edu

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