Next year is likely to be another that experiences a below norm hurricane season, according to London’s Tropical Storm Risk.
Based on current and projected climate signals, Atlantic basin tropical cyclone activity is forecast to be about 20% below the 1950-2014 long-term norm and about 30% below the recent 2005-2014 decade long norm.
TSR says its main predictor at this extended lead (six months before the 2015 hurricane season starts) is the forecast July-September trade wind speed over the Caribbean Sea and tropical North Atlantic.
This parameter influences cyclonic vorticity (the spinning up of storms) and vertical wind shear in the main hurricane track region. At present, TSR anticipates the trade wind predictor will have a small suppressing effect on activity. As a health warning, it adds that the precision of TSR’s December outlooks for upcoming Atlantic hurricane activity between 1980 and 2014 is low.
In 2014’s hurricane season there were eight tropical storms, six hurricanes, two major hurricanes and a wind energy ACE index of 65. It was the second year in a row with activity in the lowest tercile (below-norm category); the last two consecutive below-norm activity years were 1993 and 1994.
The US has now gone nine years without a major hurricane landfall, which is an unprecedented run in hurricane records dating back to 1851, TSR said.
All forecasts performed well in 2014 - except for the TSR December forecast, which over-predicted activity. Forecast precision improved in general with proximity to the hurricane main season start on August 1. CSU performed best for predicting the ACE index whilst TSR and the Met Office performed best for predicting hurricane numbers. All agencies over-predicted tropical storm numbers although the Institute of Meteorology, Cuba forecasts were closest overall.
Updated TSR outlooks will be issued on April 8 2015, May 27 2015, June 5 2015, July 6 2015 and August 5 2015.
The TSR scientific grouping brings together meteorologists, climatologists and statisticians from University College London and Aon Benfield.