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Re: [P&C] Botched 2006 Atlantic hurricane forecasts

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  • npat1
    NOAA PRESS RELEASE NOAA: August 2006 Update to Atlantic Hurricane Season Outlook Issued: 8 August 2006 Realtime monitoring of tropical Atlantic conditions
    Message 1 of 1 , Dec 4, 2006

      NOAA: August 2006 Update to Atlantic Hurricane Season Outlook

      Issued: 8 August 2006

      Realtime monitoring of tropical Atlantic conditions
      Realtime monitoring of tropical East Pacific conditions

      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

      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 Ni�a-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.


      1. Expected Activity - 75% chance above normal, 20% chance near
      normal, 5% chance below normal

      An important measure of the total seasonal activity is NOAA�s ACE
      index, which accounts for the collective intensity and duration of
      Atlantic named storms and hurricanes during a given hurricane season.
      The ACE index is also used to define above-, near-, and below-normal
      hurricane seasons (see Background Information). A value of 117% of the
      median (Median value is 87.5) corresponds to the lower boundary for an
      above-normal season.

      For the 2006 Atlantic hurricane season, the expected ACE range is 110%-
      170% of the median. Based on this range and on the 75% probability of
      an above-normal season, we expect a seasonal total of 12-15 named
      storms, 7-9 hurricanes, and 3-4 major hurricanes. This predicted ACE
      range can be satisfied even if the numbers of named storms,
      hurricanes, or major hurricanes fall outside their expected ranges.

      The vast majority of named storms and hurricanes are expected to form
      during August-October over the tropical Atlantic Ocean, which is
      typical for above-normal seasons. These systems generally track
      westward toward the Caribbean Sea and/or United States as they
      strengthen. NOAA does not currently make seasonal forecasts for
      landfalling hurricanes. However, similar above-normal seasons have
      historically averaged 2-3 landfalling hurricanes in the continental
      United States and 2-3 hurricanes in the region around the Caribbean

      The conditions that produce hurricane landfalls are very difficult to
      predict at these extended ranges. As a result, it is currently not
      possible as part of this outlook to predict the number or intensity of
      landfalling hurricanes, or whether a given locality will be impacted
      by a hurricane this season. It is important that residents and
      government officials in hurricane-vulnerable communities have a
      hurricane preparedness plan in place.

      2. Expected Climate Conditions � Active multi-decadal signal, above-
      average Atlantic Ocean temperatures

      All of the Atlantic hurricane seasons since 1995 have been above
      normal, with the exception of two moderate to strong El Ni�o years
      (1997 and 2002). This contrasts sharply with the 1971-1994 period of
      generally below-normal activity (Goldenberg et al., Science, 2001).
      The regional atmospheric circulation anomalies contributing to these
      long-period fluctuations in hurricane activity is strongly linked to
      the tropics-wide multi-decadal signal (Bell and Chelliah, 2006). Since
      1995 this signal has been very conducive to above-normal hurricane
      seasons and warmer Atlantic SSTs, and it is again the main factor
      guiding the 2006 outlook.

      Over the North Atlantic, key aspects of the multi-decadal signal
      expected during the 2006 hurricane season include 1) warmer SSTs,
      lower surface air pressure, and increased moisture across the tropical
      Atlantic, 2) an amplified ridge at upper levels across the central and
      eastern subtropical North Atlantic, 3) reduced vertical wind shear in
      the deep tropics over the central North Atlantic, which results from
      easterly wind anomalies in the upper atmosphere (green arrows) and
      weaker easterly trade winds in the lower atmosphere (dark blue
      arrows), and 4) weaker easterly winds in the middle and lower
      atmosphere, resulting in a configuration of the African easterly jet
      (wavy blue arrow) that favors hurricane development from tropical
      waves moving westward from the African coast.

      This outlook calls for a lower level of activity than was predicted on
      22 May 2006. The May forecast called for 13-16 Tropical Storms, 8-10
      Hurricanes, and 4-6 Major Hurricanes. The chances of an extremely
      active season are now lower for three reasons: 1) neither the
      atmospheric wind and air pressure patterns, nor the tropical Atlantic
      SSTs, are as conducive as expected; 2) long periods of suppressed
      convection near the date line, which acts to lower the vertical wind
      shear over the tropical Atlantic, are no longer present, 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.

      One factor known to significantly impact Atlantic hurricane seasons is
      ENSO (Gray, 1984). El Ni�o favors fewer hurricanes and La Ni�a favors
      more hurricanes. Based on the most recent ENSO outlook issued by
      NOAA�s Climate Prediction Center, ENSO-neutral conditions are expected
      in the tropical Pacific through much of the Atlantic hurricane season.
      Therefore, ENSO is not expected to impact this hurricane season.

      3. Multi-decadal fluctuations in Atlantic hurricane activity

      Atlantic hurricane seasons exhibit prolonged periods lasting several
      decades of generally above-normal or below-normal activity. These
      fluctuations in hurricane activity result almost entirely from
      differences in the number of hurricanes and major hurricanes forming
      from tropical storms first named in the main development region, which
      spans the tropical Atlantic Ocean and Caribbean Sea.

      Hurricane seasons during 1995-2005 have averaged 15 named storms, 8.5
      hurricanes, and 4 major hurricanes, with an average ACE index of 179%
      of the median. NOAA classifies nine of the last eleven hurricane
      seasons as above normal, and seven as hyperactive (ACE > 175% of
      median). In contrast, during the preceding 1971-1994 period, hurricane
      seasons averaged 8.5 named storms, 5 hurricanes, and 1.5 major
      hurricanes, with an average ACE index of only 75% of the median. One-
      half of these seasons were below normal, only three were above normal
      (1980, 1988, 1989), and none were hyperactive.

      4. Uncertainties in the Outlook

      The main uncertainty in this outlook is related to the strong
      variability in atmospheric and oceanic conditions across the tropical
      Atlantic in recent months. This variability is partly related to
      strong intraseasonal fluctuations in convection and upper-level
      divergence over the central equatorial Pacific. Current conditions are
      only modestly conducive to an above-normal season, although they may
      become even more conducive as impacts fade from the enhanced
      convection over the central equatorial Pacific during mid-June through

      Another uncertainty is the upper-level circulation anomalies over the
      eastern U.S. and western North Atlantic. The last three hyperactive
      hurricane seasons (2003-2005) featured a persistent upper-level ridge
      in these regions. This ridge has been notably absent so far this
      season. Our only seasonal predictor for the circulation in this area
      is a significant El Ni�o or La Ni�a, neither of which is expected this
      season. A persistent ridge over the eastern U.S. would favor increased
      activity and more hurricane landfalls.


      1) It is currently not possible to confidently predict at these
      extended ranges the number or intensity of landfalling hurricanes, or
      whether a particular locality will be impacted by a hurricane this
      season. Therefore, residents and government agencies of coastal and
      near-coastal regions should always maintain hurricane preparedness
      efforts regardless of the overall seasonal outlook.

      2) Far more damage can be done by one major hurricane hitting a
      heavily populated area than by several hurricanes hitting sparsely
      populated areas. Therefore, hurricane-spawned disasters can occur even
      in years with near-normal or below-normal levels of activity.
      Examples of years with near-normal activity that featured extensive
      hurricane damage and numerous fatalities include 1960 (Hurricane
      Donna), 1979 (Hurricanes David and Frederic), and 1985 (Hurricanes
      Elena, Gloria and Juan). Moreover, the nation's second most damaging
      hurricane, Andrew in 1992, occurred during a season with otherwise
      below normal activity.


      Climate Prediction Center
      Dr. Gerald Bell, Meteorologist; Gerry.Bell@...
      Dr. Muthuvel Chelliah, Physical Scientist; Muthuvel.Chelliah@...
      Dr. Kingste Mo, Meteorologist; Kingste.Mo@...

      National Hurricane Center
      Eric Blake, Meteorologist; Eric.S.Blake@...
      Dr. Christopher Landsea, Meteorologist; Chris.Landsea@...
      Dr. Richard Pasch, Meteorologist; Richard.J.Pasch@...

      Hurricane Research Division
      Stanley Goldenberg, Meteorologist; Stanley.Goldenberg@...


      Bell, G. D., and M. Chelliah, 2006: Leading tropical modes associated
      with interannual and multi-decadal fluctuations in North Atlantic
      hurricane activity. J. Climate. 19, 590-612.

      Bell, G. D., and Co-authors 2004: The 2003 Atlantic Hurricane Season:
      A Climate Perspective. State of the Climate in 2003. A. M. Waple and
      J. H. Lawrimore, Eds. Bull. Amer. Meteor. Soc., 85, S1-S68.

      Bell, G. D., and Co-authors 2005: The 2004 Atlantic Hurricane Season:
      A Climate Perspective. State of the Climate in 2004. A. M. Waple and
      J. H. Lawrimore, Eds. Bull. Amer. Meteor. Soc., 86, S1-S68.

      Bell, G. D., and Co-authors 2006: The 2005 Atlantic Hurricane Season:
      A Climate Perspective. State of the Climate in 2004. A. M. Waple and
      J. H. Lawrimore, Eds. Bull. Amer. Meteor. Soc., 87, S1-S78.

      Bell, G. D., and M. S. Halpert, 2000: Climate Assessment for 1999.
      Bull. Amer. Meteor. Soc., 81, S1-S51.

      Goldenberg, S. B., C. W. Landsea, A. M. Mestas-Nu�ez, and W. M. Gray,
      2001: The recent increase in Atlantic hurricane activity: Causes and
      implications. Science, 293, 474-479.

      Gray, W. M., 1984: Atlantic seasonal hurricane frequency: Part I: El
      Ni�o and 30-mb quasi-bienniel oscillation influences. Mon. Wea. Rev.,
      112, 1649-1668.
      NOAA/ National Weather Service
      National Centers for Environmental Prediction
      Climate Prediction Center
      5200 Auth Road
      Camp Springs, Maryland 20746
      Page Author: Climate Prediction Center Internet Team
      Page last modified: August 8, 2006


      -- "npat1" <npat1@...> wrote:

      By Philip J. Klotzbach and William M. Gray

      We continue to foresee another very active Atlantic basin tropical
      cyclone season in 2006. Landfall probabilities for the 2006 hurricane
      season are well above their long-period averages. (4 April 2006)


      Information obtained through March 2006 continues to indicate that the
      2006 Atlantic hurricane season will be much more active than the
      average 1950-2000 season. We estimate that 2006 will have about 9
      hurricanes (average is 5.9), 17 named storms (average is 9.6), 85 named
      storm days (average is 49.1), 45 hurricane days (average is 24.5), 5
      intense (Category 3-4-5) hurricanes (average is 2.3) and 13 intense
      hurricane days (average is 5.0). The probability of U.S. major
      hurricane landfall is estimated to be about 55 percent above the
      long-period average. We expect Atlantic basin Net Tropical Cyclone
      (NTC) activity in 2006 to be about 195 percent of the long-term

      Department of Atmospheric Science
      Colorado State University
      Fort Collins, CO


      The second author gratefully acknowledges valuable input to his CSU
      research project over many years by former graduate students and now
      colleagues Chris Landsea, John Knaff and Eric Blake. We also thank
      Professors Paul Mielke and Ken Berry of Colorado State University for
      much statistical analysis and advice over many years.

      The second author would further like to acknowledge the encouragement
      he has received for this type of forecasting research application from
      Neil Frank, Robert Sheets, Robert Burpee, Jerry Jarrell, former
      directors of the National Hurricane Center (NHC), and from the current
      director, Max Mayfield and their forecast staffs.



      Pat N
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