In a release issued on Tuesday, Professor Mark Saunders and Dr Adam Lea said that based on current and projected climate signals, North Atlantic basin tropical cyclone activity in 2013 is forecast to be about 20 percent above the long-term (1950-2012) norm and 20 percent below the recent 2003-2012 10-year norm.
The TSR experts noted that United States landfalling hurricane activity is forecast to be close to the 2003-2012 10-year norm.
The revised TSR forecast now predicts:
15 tropical storms including seven hurricanes and three intense hurricanes. This compares to long-term norms of 11, six and three respectively.
An ACE (Accumulated Cyclone Energy) value of 121 (up slightly from the July forecast of 112). The long-term norm is 103.
A 49 percent likelihood that activity will be in the top one-third of years historically (up slightly from the July forecast likelihood of 42 percent).
Four tropical storm and two hurricane landfalls on the US mainland.
TSR’s two predictors for basin activity are the forecast July-September trade wind speed over the Caribbean and tropical North Atlantic, and the forecast August-September 2013 sea surface temperatures in the tropical North Atlantic. The former influences cyclonic vorticity (the spinning up of storms) in the main hurricane track region, while the latter provides heat and moisture to power incipient storms in the main track region.
The TSR basin forecast has increased slightly since early July because North Atlantic August-September sea surface temperatures are now expected to be slightly warmer than thought previously.
TSR’s outlook for US hurricane landfalls employs July tropospheric wind anomalies over North America, the East Pacific and North Atlantic.
The precision of TSR’s August forecasts between 1980 and 2012 is high for upcoming Atlantic hurricane activity and moderate for US hurricane activity.
On the other side of the Atlantic, although forecasters at Colorado State University (CSU) have lowered their prediction for the 2013 season slightly, weather gurus Philip J. Klotzbach and William M. Gray continue to anticipate an above-average season.
They estimate about eight hurricanes, including three major (Category 3-4-5) hurricanes, and 14 named storms.
“The probability of US major hurricane landfall and Caribbean major hurricane activity for the remainder of the 2013 season is estimated to be above its long-period average,” the two forecasters said.