In another forecast of a mild 2009 hurricane season, the UK-based Meteorological Office (Met Office) said it expects only six tropical storms to occur in the North Atlantic between July and November, well below the long-term average of 12.4. There were 15 North Atlantic storms during the 2008 hurricane season.

Using a model that simulates ocean-atmosphere processes and interactions, which determine tropical storm development, Met Office said there is a 70% chance that there will be three to nine storms in the North Atlantic during the hurricane season. The accumulated cyclone energy (ACE) index is forecast to be 60, less than half the long-term average of 131 and far below the 2008 hurricane season’s 141. The ACE index includes storm lifetimes and intensities, as well as total numbers of storms, to measure the combined intensity and duration of all tropical storms during a season.

The consensus among forecasters has been for a relatively calm hurricane season. Colorado State University (CSU) forecasters, who had initially called for 14 named storms to develop in the Atlantic and Caribbean between June 1 and Nov. 30, have twice cut their forecast and now predict a 11 named storms, including five hurricanes, two of them intense (Category Three or greater) (see NGI, June 8). Currently neutral El Nino/southern oscillation conditions that could transition to weak El Nino conditions, the persistence of anomalously cool sea surface temperatures in the tropical Atlantic and a stronger-than-normal Azores High during April-May all contributed to the revised forecast, according to CSU.

Other forecasters calling for a relatively mild hurricane season include WSI Corp. (see NGI, June 1), the National Oceanic and Atmospheric Administration (NOAA) (see NGI, May 25) and AccuWeather.com Chief Long Range Forecaster Joe Bastardi (see NGI, May 18).

A total of 16 named storms, including eight hurricanes, five of them intense, formed during the 2008 season. According to NOAA, an average Atlantic hurricane season has 11 named storms, including two major hurricanes.

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