BRIDGETOWN, Barbados, Wednesday May 30, 2012 – The good news is that the latest forecast for the 2012 Atlantic hurricane season is close to the long-term norm. The not-so-good-news is that the May prediction has been revised upward, calling for slightly more activity than was forecast in April.
Tropical Storm Risk (TSR), which provides real-time mapping and prediction of tropical cyclone windfields worldwide, has released its pre-season outlook for the 2012 Atlantic hurricane season, running from 1 June to 30 November.
The outlook anticipates Atlantic basin and United States landfalling hurricane activity being close to their long-term (1950-2010) norm values but 10-40% below their norm values for the last 10-years (2002-2011).
TSR, part of Aon Benfield Research’s academic and industry collaboration, slightly raised its April forecast. The pre-season outlook now includes:
• A 34% probability of an above-normal Atlantic hurricane season, a 36% probability of a near-normal season, and a 30% chance of a below-normal season. • 13 tropical storms including six hurricanes and three intense hurricanes. This compares to long-term norms of 11, six and three respectively. • An ACE (Accumulated Cyclone Energy) value of 98. The long-term norm is 103.
For U.S. landfalling activity referenced to long-term norm values, TSR forecasts:
• A 48% probability of above-normal U.S. landfalling hurricane activity; a 26% likelihood of a near-normal season, and a 26% chance of a below-normal season. • Four tropical storm strikes on the U.S., including two hurricanes. This compares to long-term norms of three and 1.5 respectively.
Three main climate factors will determine the level of hurricane activity in the Atlantic basin. Occurring in August and September, these are the speed of trade winds over the tropical North Atlantic, sea temperatures in the tropical North Atlantic, and the sign and strength of El Nino Southern Oscillation.
U.S. landfalling hurricane activity is influenced by July tropospheric wind patterns over the North Atlantic and U.S., and by the level of hurricane activity occurring at sea.
Professor Mark Saunders at Tropical Storm Risk, said: “At present the main climate indicators point to the 2012 hurricane season being close to norm. However, uncertainties remain and we are overdue US landfalling hurricane strikes. Only one hurricane (Irene) has struck the US in the last 3 years and no major hurricane has struck the US since Wilma in 2005. On average 4 or 5 landfalling hurricanes would strike the US in 3 years and 4 major hurricanes would strike over 6 years. Nature has a habit of correcting herself.”
Despite the success of recent basin forecasts, sources of uncertainty remain. Model projections of ENSO (El Nino Southern Oscillation) conditions for August-September currently show a range from neutral to moderate.
There is uncertainty in how warm the tropical North Atlantic Ocean will be in August-September. Also variance exists in the level of basin hurricane activity possible from the same August-September climate factors and, as seen in recent years, even larger variance exists in the level of US landfalling hurricane activity possible from the same basin activity.
The 2012 Atlantic hurricane season was jump-started on May 19 with the formation of Tropical Storm Alberto east-southeast of Charleston, South Carolina. Alberto posed no threat to the Caribbean.