May update raises forecast for 2012 hurricane season


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.

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