Re: [P&C] Botched 2006 Atlantic hurricane forecasts
- NOAA PRESS RELEASE
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
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.,
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:
EXTENDED RANGE FORECAST OF ATLANTIC SEASONAL HURRICANE ACTIVITY AND
U.S. LANDFALL STRIKE PROBABILITY FOR 2006
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.