Hurricane Season 2018
The 2018 hurricane season overall was slightly above average. The season was characterized by above-average numbers of named storms and hurricanes and nearaverage numbers of major hurricanes. Our initial seasonal forecast issued in April correctly predicted a slightly above-average season, while later seasonal forecasts underestimated Atlantic hurricane activity. These downward adjustments were primarily due to anomalous tropical Atlantic SST cooling. Despite a relatively cold tropical Atlantic, early September 2018 was extremely active and was the primary driver of the slightly above-average season that occurred. In addition, six of the fifteen named storms that formed in 2018 were initially classified as subtropical, and these types of systems that form in the subtropics do not respond to large-scale tropical climate drivers in the same way that TCs forming in the tropics do. Six consecutive two-week forecasts were issued during the peak months of the Atlantic hurricane season from August-October. These forecasts were based on current hurricane activity, predicted activity by global forecast models and the phase of the Madden-Julian Oscillation (MJO). These two-week forecasts generally verified well, although the extremely active early September was underestimated by the two-week forecasts. Integrated measures such as Net Tropical Cyclone (NTC) activity and Accumulated Cyclone Energy (ACE) were slightly above average. Tropical Atlantic sea surface temperatures were somewhat cooler than normal during the peak of the 2018 hurricane season. Caribbean shear was very strong, which likely was responsible for the lack of activity observed in this region. However, shear was slightly below normal in the eastern part of the Atlantic, favoring TC formations in the eastern and central tropical Atlantic. The 2018 Atlantic hurricane season will primarily be known for two hurricanes that brought significant damage and loss of life to the continental United States. Hurricane Florence made landfall as a Category 1 hurricane, but like Harvey last year, the storm then slowed considerably, bringing record flooding to portions of North and South Carolina. Hurricane Michael made landfall as a Category 4 hurricane in the Florida Panhandle, bringing devastating wind and storm surge damage.
By Philip J. Klotzbach and Michael M. Bell
In Memory of William M. Gray