Academics issue updated Atlantic hurricane season outlook

An academic and industry collaboration part of Aon Benfield Research has issued an updated forecast for the 2013 Atlantic hurricane season.

Prof. Mark Saunders and Dr. Adam Lea from Tropical Storm Risk are now predicting 15 named storms, seven hurricanes and three major hurricanes (Category 3 or higher), a slight reduction from their forecast in June, when the season began.

That’s still an above-normal hurricane season, though, about 20% above the norm between 1950 and 2012. However, the forecast is about 20% below the more recent 2003-2012 norm, Aon said.

Saunders and Lea currently project that there is a 49% probability that the 2013 Atlantic hurricane season Accumulated Cyclone Energy (ACE) Index will be above-average, a 41% likelihood it will be near-normal, and a 10% chance it will be below-normal.

They made the change in their forecast for a couple of different reasons.

“The first factor is that current forecast computer model projections indicate that trade winds over the Caribbean Sea and the tropical North Atlantic will be slightly below normal through September,” their report said.

“These lighter winds help influence the level of cyclonic vorticity (the spinning up of storms) in the main development region (MDR) of the Atlantic.

The second factor is that sea surface temperatures in the Atlantic’s MDR are expected to be slightly above normal and poised to provide a slight enhancing effect for cyclogenesis during the months of August and September. Both of these factors are based on 1980-2012 climatology.”

The Atlantic hurricane season runs to the end of November. There have been four tropical storms so far.