Tuesday, August 08, 2006

NOAA: August 2006 Update to Atlantic Hurricane Season Outlook

Issued: 8 August 2006

Atlantic Hurricane Outlook & Seasonal Climate Summary Archive


NOAA continues to predict a high likelihood (75% chance) of an above-normal 2006 Atlantic hurricane season and a 20% chance of a near-normal season, according to a consensus of scientists at National Oceanic and Atmospheric Administration's (NOAA) Climate Prediction Center (CPC), National Hurricane Center (NHC), and Hurricane Research Division (HRD). Therefore, 2006 is forecast to be the tenth above-normal season in the last twelve years. See NOAA’s definitions of above-, near-, and below-normal seasons.

This updated outlook calls for a seasonal total of 12-15 named storms, with 7-9 becoming hurricanes, and 3-4 becoming major hurricanes (categories 3-5 on the Saffir-Simpson hurricane intensity scale). The likely range of NOAA’s Accumulated Cyclone Energy (ACE) index (Bell and Halpert, 2000) is 110%-170% of the median. These totals include the three tropical storms (Alberto, Beryl, and Chris) that have already occurred. Therefore, for the remainder of the season, we expect an additional 9-12 named storms, 7-9 hurricanes, and 3-4 major hurricanes.

The predicted 2006 activity mainly reflects a continuation of conditions associated with the multi-decadal signal, which has favored above-normal Atlantic hurricane seasons since 1995. These conditions include warmer than average sea surface temperatures (SSTs), lower vertical wind shear, reduced sea level pressure, and a more conducive structure of the African easterly jet.

While we are predicting an active season, a repeat of last year’s record season is unlikely. The season is also expected to be slightly less active than previously forecast on 22 May 2006, when 13-16 Named Storms, 8-10 hurricanes, and 4-6 major hurricanes were predicted. The expected activity is lower for three reasons: 1) atmospheric and oceanic conditions are not as conducive as previously forecast, 2) the transition away from La NiƱa-like rainfall patterns occurred more quickly than expected, and 3) the very persistent upper-level ridge pattern over the eastern U.S. and western Atlantic, which contributed to the extremely active 2003-2005 hurricane seasons, is not present.


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