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Seasonal Forecast
CSU
Forecast Team Predicts Above-Average Hurricane Activity in 2003
With
El Nino conditions ending, expectations increase for at least one
major hurricane making landfall.
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Extended Range Hurricane
Forecast For 2003
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Tropical Cyclone Parameters and 1950-2000
Climatology (in parentheses).
Released Dec. 6, 2002
Named Storms (9.6)* 12
Named Storm Days (49.1) 65
Hurricanes (5.9) 8
Hurricane Days (24.5) 35
Intense Hurricane Days (5.0) 8
Hurricane Destruction Potential (72.7) 100
Net Tropical Cyclone 140
*Number in parentheses represents average year totals based
on 1950-2000 data. |
Following a suppressed
2002 hurricane season, renowned Colorado State University (CSU) tropical
storm researcher William Gray and his forecast team predict Atlantic
basin hurricane activity to be well above average in 2003—including
twice as many hurricanes as in the previous year.
For their first extended-range forecast for 2003, issued December
6, 2002, Gray and his colleagues predict 12 named tropical storms
will form in the Atlantic basin between June 1 and November 30. Of
these, eight will become hurricanes and three are anticipated to evolve
into intense hurricanes (Saffir/Simpson category 3, 4, 5) with sustained
winds of 111 mph or greater. The long-term average is 9.6 tropical
storms, 5.9 hurricanes and 2.3 intense hurricanes per year.
Last year witnessed 12 named storms, but only four hurricanes and
two intense hurricanes. (See HP, Winter 2003, page 13 for the National
Oceanic and Atmospheric Administration’s [NOAA] 2002 seasonal
review.) NOAA also issues Atlantic basin seasonal hurricane forecasts,
which are independent of the CSU forecasts. They utilize prior Colorado
State research, but are augmented with NOAA’s own insights. The
two forecasts do not always agree.
“Information we have obtained and analyzed through November indicates
that 2003 will be an active Atlantic hurricane season with above-average
activity,” said Gray. “We expect Atlantic basin tropical
cyclone activity to be about 140 percent of average this upcoming
[season].”
LANDFALL PROBABILITIES
Based in Fort Collins, CO, the team’s forecast said that an analysis
of current and projected global climate signals indicates that Atlantic
tropical cyclone activity should be more active than normal during
2003.
According to Gray, the increased activity is due in large part to
a predicted termination of current El Niño conditions and an
anticipation of warm sea surface temperatures in the north and tropical
Atlantic. A moderate El Niño and uncharacteristically cool
temperatures in the tropical Atlantic helped to inhibit hurricane
activity in 2002.
Gray and his team also call for an increased probability of at least
one intense hurricane making landfall in the United States in 2003.
“The probability of a major hurricane making U.S. landfall in
2003 is 30 percent higher than in the average season,” said Gray.
According to the forecast, there is a 68 percent chance of a major
hurricane hitting somewhere along the U.S. coastline in 2003 (the
last century’s average probability was 52 percent). For the U.S.
East Coast, including the Florida Peninsula, the probability of an
intense hurricane making landfall is 48 percent. For the Gulf Coast—from
the Florida Panhandle west to Brownsville, TX—the probability
is 38 percent.
EXTREMELY LUCKY
The last eight years have witnessed 106 named storms, 62 hurricanes
and 29 major hurricanes in the Atlantic basin. During that period,
only four of the 29 major hurricanes (Opal, Bret, Fran and Lili) crossed
the U.S. coastline. Based on historical averages, one in three major
hurricanes comes ashore in the United States. Before Lili made landfall
in October 2002, a record 21 consecutive Atlantic basin hurricanes
did not make shore along the U.S. coast.
“The United States has been extremely lucky over the past eight
years, but climatology will eventually right itself and we must expect
a great increase in landfalling intense hurricanes,” said Gray.
“With such large coastal population growth in recent decades,
it is inevitable that we will see hurricane-spawned destruction in
coming years on a scale many times greater than what we have seen
in the past.”
Major hurricanes account for about a quarter of all named storms,
but when normalized for population, inflation and wealth per capita,
they cause about 85 percent of all tropical cyclone-spawned destruction.
The storm seasons spanning 1995-2002 comprise the most active eight
consecutive hurricane years on record and the Colorado State forecasting
team believes we are in a new multi-decadal era for increased storm
activity such as occurred in the 1940s and 1950s. They add that, in
this new era as in the past, there will be individual years with below-average
numbers of hurricanes. According to the team, 2002 was one of those
temporary deviations from the long-period average.
EVOLVING TECHNIQUES
For the December forecast, Gray and his research team are using a
recently developed six- to 11-month statistical forecast system based
on 51 years of past storm season data. The new system, which provides
strong statistical relationships for climate data, is expected to
improve extended-range forecasts. For a detailed description of the
forecast factors, visit the CSU Web site at typhoon.atmos.colostate.edu/forecasts.
“Our evolving forecast techniques are based on a wide variety
of climate-related global and regional predictors previously shown
to be related to forthcoming seasonal Atlantic tropical cyclone activity
and landfall probability,” said forecast team member Philip Klotzbach.
“This forecast is based on atmospheric and oceanic conditions
similar to what is currently observed and what we anticipate to be
in place throughout the 2003 hurricane season.”
Gray, in his 20th year of forecasting Atlantic basin storms, believes
that these and other recent improvements in the gathering, archival
and data analysis techniques of global atmospheric and oceanic signals
can be used to continually improve forecasts of Atlantic
basin hurricane activity and landfall probabilities.
“Overall, we are making very good progress on improving statistical
hurricane forecasting techniques and in better understanding why there
is such variability in month-to-month and year-to-year Atlantic basin
hurricane activity,” said Gray. “We feel our ongoing forecast
research is allowing us to continually improve hurricane prediction
skill.”
The Colorado State forecast team does not attribute changes in recent
and projected Atlantic hurricane activity to human-induced global
warming.
In addition to Gray and Klotzbach, Colorado State forecast team members
include Christopher Landsea, John Sheaffer and others. The team will
issue seasonal updates of the 2003 Atlantic basic hurricane activity
forecast on May 30, August 7 and September 3. The August forecast
will include separate monthly forecasts for August-only and September-only
activity.
| Lifetime Of Weather Research,
Forecasting |
Professor William Gray joined Colorado State University’s
Department of Atmospheric Science in 1961 after spending four
years as a research assistant in the Department of Meteorology
at the University of Chicago. Prior to that he spent four years
as an Air Force officer forecasting weather.
Gray’s research involves studies of tropical cyclones genesis,
structure intensity change and motion. He also studies seasonal
weather prediction and the physical processes associated with
ENSO and monsoon variability. His active research interests
include studies of large-scale tropical meteorology with links
to broader, global scale climate related processes. His current
research work can be broadly lumped into three main areas:
• Tropical Cyclones: Studies are directed toward
expanding our knowledge of the basic physical processes governing
tropical cyclone formation, structure and intensity change.
Evaluating several new hypotheses concerning the processes influencing
maximum potential intensity, rates of intensification, the size
of tropical cyclone circulations and the structure and basic
dynamics of the inner core and eye regions.
• Tropical Diurnal Cycle: Presently, the subsidence
cycle which drives morning maximum of intense tropical oceanic
convection is not well simulated in numerical climate models.
Consequently, studying the associated deep radiative cooling
and convective heating processes, which also are poorly represented
in these models.
• Forecasting Seasonal Hurricane
Activity and the Associated Global Climate Variability:
This program entails the analysis and further development of
basic scientific concepts related to extended range quantitative
climate forecast schemes for Atlantic basin seasonal hurricane
activity, selective regional Asian monsoon rainfall, and of
the potential for seasonal predictability in the middle latitudes.
Along with the basic science concerning underlying physical
mechanisms, this work seeks accuracy at nine to 14 month forecast
lead times; sufficient to allow meaningful mitigating actions.
Gray has been recognized for his many scientific achievements.
Among his awards and honors are: Fellow, American Meteorological
Society (AMS); co-recipient of AMS Banner I. Miller Award (1993);
AMS Jule L. Charney Award (1993); and the Neil Frank Award of
the National Hurricane Conference (April 14, 1995), “for
pioneering research into long-range hurricane forecasting and
for developing a better understanding of how global climatological
conditions shape the creation and intensity of tropical cyclones.” |
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