AIRCurrents
A Look Back at the 2005 Hurricane
Season—Lessons Learned
Editor’s note: This year marks the fifth anniversary of the 2005 Atlantic
11.2010
Just before the June 1st official start of the 2010 Atlantic
hurricane season, all of the major weather forecasters
projected that 2010 would be an especially active year.
The National Oceanic and Atmospheric Administration
(NOAA) forecast that 2010 would bring 14-23 named
storms, 8-14 of which would be hurricanes, and 3-7 of
which would be major hurricanes (Category 3 or higher
on the Saffir-Simpson Hurricane Wind Scale). On average,
about 11 named storms develop every season, six of
which become hurricanes. An average season will see just
three of those hurricanes develop into major hurricanes.
The predictions had already been borne out by midOctober. With a quarter of the season still remaining,
16 storms had been named, nine of which became
hurricanes, five of them major hurricanes. Eight named
storms developed in September alone, tying 2002 and
2007 for the most tropical cyclones ever recorded in that
month; and for only the second time in more than a
century, two Category 4 hurricanes, Igor and Julia, were
active in the Atlantic at the same time.
hurricane season—the most active on record and the year Katrina came.
AIR’s Dr. Tim Doggett, Principal Scientist, Atmospheric Science, remembers
2005 in the context of this year’s activity and discusses some of the 2005
season’s continuing legacies.
by Dr. Tim Doggett
There has not been a season this active since 2005; and
while the fifth anniversary of Hurricane Katrina’s onslaught
on New Orleans and the Gulf Coast was widely covered,
it is also worth remembering the 2005 season as a
whole. Certainly, the outcomes of these two highly active
seasons—2010 and 2005—were very different.
The 2005 Hurricane Season
In 2005, the National Hurricane Center ran out of letters
of the English alphabet and had to continue on in Greek.
Twenty-eight named storms developed, the most to form
in a single season since record-keeping began. Fifteen of
the 28 named storms became hurricanes, the most on
record. In 2005—out of seven major hurricanes—four
achieved Category 5 status, yet another record. Four major
hurricanes—Dennis, Katrina, Rita, and Wilma—made
landfall in the United States; again, a new record.
AIRCurrents
11.10|A Look Back at the 2005 Hurricane Season—Lessons Learned
By: tim doggett
The ACE index for the season—that is, the Accumulated
Cyclone Energy Index, which is a measure of the collective
intensity and duration of all storms in a season—was the
highest ever, at 248. The average ACE is 93. Finally, the
2005 season was the costliest in history: inflicting close to
$60 billion of insured onshore losses according to Property
Claims Services (PCS)—with overall damage generally
estimated at about $150 billion (2005USD). Nearly 4,000
lives were lost.
Lessons Learned
Whatever the specific driver or confluence of drivers that
gave rise to the 2005 hurricane season, the season’s
extraordinary performance—following on the heels of a
very active 2004—prompted new analysis and vigorous
discussion in the science and modeling communities, and
in the halls of government. This evaluation continues
to this day, but already it has had effects on modeling
practice, data gathering, and increased attention on the
adoption and enforcement of building codes. Emergency
management agencies at all levels were overhauled, and
several hurricane states have invested significant funds into
researching the costs and benefits of mitigation measures
and appropriate insurance incentives.
Damage Functions Revisited
With respect to catastrophe modeling, the 2005 season
provided wind engineers with a wealth of damage
information. There was no shortage of destroyed and
damaged buildings of all types to study. Findings from
post-disaster field surveys, published academic research and
claims data, coupled with unparalleled wind observation
datasets contributed to more comprehensive model
validation tests, a better understanding of the extent
and kinds of damage to be found in situ, and a fuller
appreciation of the variety of residential and commercial
building types and their vulnerabilities.
Indeed AIR has been working continuously since 2005 to
analyze the information and incorporate findings to improve
the way the AIR U.S. Hurricane Model differentiates risks.
The sheer number of affected wood frame and masonry
buildings, for example, provided a realization (and then
confirmation) of the greater vulnerability of commercial
buildings of these construction types than had been
understood previously. A greater vulnerability of high-rise
buildings was similarly revealed.
This expanded information base allowed damage functions
to be refined. Similarly, new occupancies were identified
as being significant drivers of loss and damage functions
were introduced for, among others, airplane hangars,
auto repair shops, gas stations, golf courses, restaurants
and schools—reflecting the fact that buildings that have
similar shapes or construction histories do not always have
the same vulnerabilities. Additionally, the importance of
“Business Interruption” to overall insured losses became
better appreciated and understood, initiating new efforts to
more accurately model the phenomenon.
The new data enabled a new and exhaustive analysis at AIR
of the evolution and enforcement of building codes across
all states and their impact—as a continuous function of
time—on the existing building inventory. Findings of that
study were incorporated in the Spring 2010 release (Version
12.0) of the AIR Hurricane Model.
Ultimately, the unprecedented wealth of data has resulted
in an additional level of detail in both the hazard and
vulnerability components of the AIR model that enables
better differentiation between risks. Companies will benefit
from this improved risk differentiation at every point in their
workflow where they use catastrophe model outputs, from
underwriting to portfolio management to risk transfer.
New Focus on Data Quality
The sharing of insurers’ claims and exposure information
also provided insight into how undervalued many properties
were—just one aspect of the generally poor quality of
the data held by most insurers that was revealed in the
aftermath of the 2005 season. In November 2005, AIR
released a report presenting the results of an analysis of
then-current exposure data. The analysis revealed the
extent to which poor exposure data quality was limiting
companies’ ability to accurately assess their catastrophe risk.
As a result of AIR’s seminal report, data quality became
the rallying cry of the industry and regulators. And AIR has
led the response with the introduction of TruExposure—a
powerful new tool encompassing data validation, scoring,
benchmarking and augmentation that are helping insurers
and reinsurers better understand and improve their
exposure data used for catastrophe analysis.
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AIRCurrents
11.10|A Look Back at the 2005 Hurricane Season—Lessons Learned
By: tim doggett
The Warm Sea Surface Temperature Catalog
The record-breaking Atlantic tropical cyclone activity
of 2005 followed an active 2004 season, during which
Hurricanes Charley, Frances, Ivan and Jeanne all wreaked
havoc in Florida. Although sea surface temperatures (SSTs)
in the Atlantic had been elevated above the long-term
average since 1995—and AIR had been engaged in active
climate research throughout that period—few in the
industry paid much attention. That changed after the 2005
season.
In the aftermath of 2005, modelers began to explore ways
to address the possibility that, as long as SSTs remained
elevated, hurricane activity and insured losses might also
be elevated. One approach taken was a forecast of activity
in the “near term.” Recognizing the lack of skill of such
forecasts, AIR took an alternative route and introduced
a “Warm Sea Surface Temperature Condition Catalog”
(WSST) to complement its standard catalog. Both are
credible long-term views of risk, the difference being that
the WSST catalog is based on only those seasons since 1900
in which the Atlantic Ocean has been warmer than average
(observed ~50% of the time).
Importantly, AIR’s WSST catalog, like the standard catalog,
reflects landfall risk. As the current 2010 hurricane season
has made very apparent, increased activity in the Atlantic
does not directly or proportionately translate into increased
numbers of landfalls or insured losses.
U.S. Impacts
Beginning in June and continuing straight through until the
end of October, a total of seven tropical cyclones impacted
the United States in 2005.
Arlene and Cindy
Arlene was named on June 9th, soon after the official start
to the season. Two days later Arlene made landfall just
west of Pensacola, Florida, with 60 mph winds and heavy
precipitation. A month later, Cindy formed, becoming a
tropical storm on the morning of July 5th. Cindy made
landfall that same evening, near Grand Isle, Louisiana, as a
minimal Category 1 hurricane with 75 mph winds.
Cindy brought five inches of rain, a storm surge four
to six feet high along the southeastern Louisiana and
western Mississippi coasts and, to the city of New Orleans,
winds gusting to 70 mph. The storm uprooted trees,
flooded streets, and caused power outages to hundreds
of thousands of homes and businesses. New Orleans
experienced its worst power outage in forty years.
Figure 1. Tropical Storm Arlene (left) and Hurricane Cindy (right)
Dennis
The very next day, July 6th, Tropical Storm Dennis became
the next new hurricane. Dennis slammed into Cuba at
Category 4 strength and headed straight for the center of
the U.S. Gulf Coast. Having weakened over Cuba, Dennis
began to re-intensify “at a rate,” according to the NHC,
“that bordered on insane.” In less than a day, Dennis went
from Category 1 to Category 4 intensity again—to become
the strongest hurricane ever to form in the Gulf before
August. (A record broken, however, only six days later by
Hurricane Emily, which eventually made a double landfall in
Mexico.)
On July 10th Dennis made landfall at Santa Rosa Island,
between Pensacola and Navarre Beach, Florida—not far
from where Hurricane Cindy had struck less than a week
earlier and Tropical Storm Arlene before that. With winds
of about 120 mph, Dennis was a Category 3 hurricane.
Fortunately, it was a relatively fast-moving storm and it was
relatively small, with hurricane-force winds extending only
about 40 miles from its center. Compared to what had
been anticipated, the damage Dennis caused was modest,
amounting to about $1.2 billion in insured losses according
to PCS.
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AIRCurrents
11.10|A Look Back at the 2005 Hurricane Season—Lessons Learned
By: tim doggett
As Katrina approached the Gulf Coast, it weakened
somewhat but remained very large. At 6:10 local time on
August 29th it made landfall as a Category 3 hurricane
near Buras, Louisiana, at the mouth of the Mississippi
River about 40 miles southeast of New Orleans. Katrina
generated a massive storm surge. Along one 20-mile stretch
of Mississippi coast near St. Louis Bay, the wall of water was
recorded as being as much as 24 feet high. In New Orleans,
situated below sea level, floodwalls were overtopped—and
53 levees were breached.
Figure 2: Hurricane Dennis
Katrina
The 2005 hurricane season is mostly closely associated
with the tragedy that was Hurricane Katrina. Katrina
was perhaps the closest the U.S. has come to a “megacatastrophe,” having laid waste to large swaths of a major
urban center, and destroying lives and livelihoods across
three states.
Katrina formed over the Bahamas on August 23rd. On
August 25th it made landfall on Florida’s North Miami
Beach as a Category 1 hurricane with 80 mph winds.
Crossing the state in about seven hours, Katrina downed
trees and power lines, leaving more than one million
customers without electricity.
Once in the Gulf of Mexico, Katrina intensified and
also increased in size. It strengthened from a borderline
Category 2/3 hurricane to Category 5 in just nine hours,
reaching its peak intensity of about 175 mph on August
28th. More disturbing, Katrina’s hurricane-force winds
extended out more than 100 miles from the storm’s eye,
and tropical storm-force winds extended some 230 miles
out. Katrina was both extremely intense and exceptionally
large—and it was heading directly toward some 3,000 oil
and natural gas platforms. Katrina’s passage destroyed 46
major platforms and damaged 20 others.
By the next day, 80% of New Orleans was flooded—to
depths of 20 feet in many areas. Thousands of people
were stranded and took refuge on rooftops. The U.S.
Coast Guard rescued more than 33,000 people in all, more
than 12,500 by helicopter. That first day, ten thousand
people—and 30,000 over the next days—sought shelter
at the Louisiana Superdome, which had been equipped to
help just 800.
Katrina is estimated to have caused at least $41 billion in
insured onshore losses (PCS, 2005 dollars). Offshore losses
have been estimated at between $2 and $8 billion. Katrina
displaced more than a million people, forcing the largest
internal refugee diaspora in U.S. history. It killed at least
1,836 people.
Figure 4: AIR Modeled Flood Footprint for New Orleans Released in September
2005 (Source: AIR)
Ophelia
Ophelia became a tropical storm a little more than 100
miles off the Florida coast on September 7th, the day
after the forced evacuation of New Orleans was ordered.
Alarmingly, some dynamical forecast models indicated
Ophelia would move west—to eventually cross Florida and
enter the Gulf. Fortunately, it did not. After meandering for
several days, Ophelia slowly began to move north towards
the Carolinas.
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Figure 3: Hurricane Katrina
AIRCurrents
11.10|A Look Back at the 2005 Hurricane Season—Lessons Learned
By: tim doggett
Passing over the warmer waters of the Gulf Stream,
Ophelia reached its peak intensity on September 14th
with sustained winds of 85 mph. That day and the next,
Ophelia’s northern and western eyewall lashed the North
Carolina coast, but the eye hovered just off shore and
never fully made landfall.
Figure 6: Hurricane Rita
Figure 5: Hurricane Ophelia
Rita
Hurricane Rita followed in Katrina’s path through the
Gulf of Mexico almost exactly. It was the first time two
Category 5 hurricanes are known to have developed
in the Gulf in the same season. Rita reached peak
intensity—sustained winds of 180 mph, stronger than
Katrina—late on September 21st. Like Katrina, Rita was
large; its hurricane-force winds extended out 85 miles
from the center and tropical storm-force winds reached to
205 miles.
Rita similarly weakened to Category 3 strength—winds of
120 mph—just before making landfall at the Louisiana/
Texas border on September 24th. Like Katrina, Rita
generated a large storm surge along the Louisiana coast.
The just-patched Industrial Canal levee in New Orleans’s
Ninth Ward was breached even before Rita made landfall;
thereafter, several other levees also were breached, and
much of New Orleans was flooded once more.
Wilma
Wilma was named on October 17th, the first time a name
beginning with a “W” was used for a tropical cyclone since
names began to be assigned alphabetically in 1950. On
October 18th, Wilma developed a small but well-defined
eye and began to intensify rapidly. In a 30-hour period,
Wilma’s pressure dropped from 982 mb to 882 mb, the
lowest pressure ever recorded in the Atlantic—while its winds
increased to 185 mph. Wilma’s rise from tropical storm to
Category 5 hurricane, which took just 24 hours, was the
fastest intensification ever recorded in the Atlantic.
After wreaking havoc in Mexico’s Yucatan Peninsula, Wilma
entered the Gulf of Mexico. On October 24th it made landfall
as a strong Category 3 hurricane—with wind speeds of 125
mph—near Naples, Florida. It crossed the state in just four
hours, causing widespread damage. Approximately six million
people lost power. Insured losses in the U.S. totaled about
$10.3 billion, according to PCS.
Two oil refineries in Port Arthur, Texas, were damaged,
causing them to stop operations for some time, and nearly
70 oil and gas platforms in the Gulf were destroyed.
Insured onshore losses attributed by PCS to Hurricane Rita
amounted to $5.65 billion. Estimates of losses to offshore
assets range between $3 and $5 billion.
Figure 7: Hurricane Wilma
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AIRCurrents
11.10|A Look Back at the 2005 Hurricane Season—Lessons Learned
By: tim doggett
After Wilma
Wilma exhausted the names reserved for tropical cyclones
in 2005. (Not all letters of the English alphabet are used.)
For the first time ever, the National Hurricane Center
resorted to using the names of the letters of the Greek
alphabet, naming Alpha, Beta, Gamma, Delta, Epsilon, and
Zeta—although none made a U.S. landfall. Beta reached
Category 3 hurricane strength on October 30th, Epsilon
became a Category 1 hurricane on December 2nd, and
tropical storm Zeta, which formed on December 30th
and dissipated on January 6th, became the longest-lived
January tropical cyclone in the Atlantic in history.
Closing Thoughts
The figure below provides a snapshot of the 2005
and 2010 hurricane seasons. For reasons that will be
discussed in an AIR Current next month, the outcomes
of these two active seasons were very different. While
sea-surface temperatures clearly have an important
influence on activity in the basin, other climatological
factors also influence how a season develops and where
storms track, among them El Niño Southern Oscillation,
the North Atlantic Oscillation, the Saharan Air Layer, and
other similar—and perhaps not yet fully identified or
understood—phenomena.
Of course, what the maps cannot show is the human
tragedy that hurricanes are capable of causing—and did
cause in 2005.
Figure 8: 2005 Hurricane Season (left) and the 2010 Hurricane Season (right)
as of November 22 (Source: AIR)
About AIR Worldwide
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in 1987 and today models the risk from natural catastrophes and terrorism in more
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