New Orleans, fl ooded

U.S. Coast Guard photo
41

Chapter 3

Hurricanes and 

the Gulf Coast

How Hurricanes Form

A hurricane is the strongest form of a “tropical cyclone,” 

the term used to describe weather systems that develop 

over tropical or sub-tropical waters with organized thunderstorms and a well-defi ned central “eye.” 

Most Atlantic hurricanes begin as atmospheric waves that 

move westward from Africa across the tropical North 

Atlantic and Caribbean Sea. Th is stretch of ocean is known 

as the main development region. Here, warm sea-surface 

temperatures pass moisture into the atmosphere, increasing humidity levels. Winds moving in from diff erent 

directions collide with the atmospheric waves and force air 

upwards. If there is low wind shear the air will continue 

to rise. Th e storm’s energy comes from the continuous 

exchange of heat between the ocean and the atmosphere, 

which is released through the formation of clouds concentrated in the center of the forming cyclone. 

Th e appearance of a high-pressure system provides the fi nal ingredient. Th e high-pressure 

system fl oats above the storm and draws the warm ocean air upward, pushing it outward 

from the top of the gathering storm in a continuous cycle. At this point the Earth’s rotation 

gives the incoming air a counter-clockwise spin and, propelled by the warm wind currents, 

the storm moves toward the coast.1

Tracking and Predicting Hurricanes

Not all storms in the main development region become hurricanes. Oft en, preexisting 

winds will tear apart the storm as it forms. If conditions are favorable, however, scientists 

will reclassify these “tropical disturbances” into more severe storms as their sustained wind 

speed rises:

• At 23 miles per hour, the disturbance becomes a “tropical depression.”

• At 39 miles per hour, the depression becomes a “tropical storm” and gets a 

name.

• At 74 miles per hour, the tropical storm is classifi ed as a hurricane (in the 

Pacifi c, a typhoon).2

A hurricane needs a constant source of energy. In this case, from June to November, the 

warm, humid waters of the Atlantic fuel the storm as trade winds from the east and ocean 

currents direct its path.3

 Th e storm weakens if it happens to move across cool water or land, 

losing its thermal energy source.4

Th e National Hurricane Center (NHC) in Miami, Florida, determines the track, intensity, 

and landfall eff ects of a storm. Th e NHC issues 72-hour tropical cyclone track and intensity 

forecasts four times a day for all storms in the north Atlantic and northeastern Pacifi c.5

Scouting Katrina from above

U.S. Air Force photo
Chapter 3

42

A hurricane watch is issued 36 hours before hurricane conditions are expected to aff ect 

coastal areas. A warning is issued 24 hours beforehand and may remain in eff ect even if 

wind speeds drop below hurricane force to account for the possibility of hurricane-level 

storm surge.

Storm surge is wind-driven water.6 As a hurricane churns in the atmosphere, its winds 

snowball the water below toward the shoreline. Combined with normal tides, this surge can 

increase the mean water level 15 feet and push up to 100 miles inland.7

 Even if a hurricane 

has weakened by the time it has reached shore, it has been building up storm surge since a 

much earlier time, when it was much stronger. 

Th ough hurricanes are measured by their wind speeds, many scientists have come to believe 

that storm surge is far more deadly than wind, especially considering that the highly populated areas of the Atlantic seaboard and the Gulf Coast lie only 10 feet above mean sea level.8

Hurricane Andrew (1992), which carried a 17-foot storm surge into Miami’s Biscayne Bay, 

illustrated the danger. Its storm surge shoved the Belzona Barge – a 215-foot, 350-ton barge 

that had been deliberately sunk 68 feet below the surface, with a thousand tons of concrete 

resting on deck, off the coast of Florida to establish an artifi cial reef – 700 feet to the west 

along the ocean fl oor.9

 “Th e greatest potential for loss of life related to a hurricane is from 

the storm surge,” according to an offi cial with the National Oceanic and Atmospheric Administration (NOAA).10

Signifi cant progress in hurricane forecasting has prevented major loss of life in areas prone to 

hurricanes.11 Th e National Weather Service (NWS) uses the Sea, Lake, and Overland Surges 

from Hurricanes (SLOSH) computer program to predict the storm surge of an inbound 

hurricane and to map the likely impact of hurricanes of diff erent sizes, speeds, strengths, and 

tracks. Th e SLOSH program uses a storm’s barometric pressure, overall size, forward speed, 

track, and wind speed, as well as prior hurricane information and other models.12

During Hurricane Andrew in 1992, alarmed by scenes in South Florida, approximately 1.2 

million people evacuated from the New Orleans metropolitan area. While the evacuation 

almost certainly saved lives, federal hurricane experts were alarmed that offi cials in New 

Orleans expected 60 to 80 hours’ warning to complete an evacuation. During testimony 

before a Congressional committee in 1993, Robert Sheets, Ph.D., then the director of the 

NHC, warned that “We don’t have the skill meteorologically speaking to provide a suffi cient 

warning for those long lead times. Th ere is no way I am going to have 70 hours of lead time 

for New Orleans to respond to a hurricane.”13

By 2005, advances in technology, such as refi nement of satellite capabilities and improvement of pressure-measuring sensors in reconnaissance planes, had drastically increased 

the NHC’s lead times.14 By 2 p.m. ET Friday, August 26, 65 hours before Katrina made 

landfall, NHC Director Max Mayfi eld, Ph.D., was making calls to emergency offi cials in 

the Gulf Coast alerting them that a rapidly strengthening storm was heading directly for 

New Orleans.15

Hurricanes and the Gulf Coast

Th e same warm waters that give the Gulf Coast its marshy topography and humid climate 

make it a prime target for hurricanes, while demographic and economic trends have multiplied their potential impact.16 In earlier periods of our history, the physical impact of major 

hurricanes in the Gulf was soft ened by swamps, marshes, and barrier islands, while the 

societal impact was limited by its relatively small concentrations of buildings and people.

In more recent times, however, the population in the coastal counties from Texas to the 

Florida Keys has soared. Th e U.S. Census Bureau reports that 9.46 million people live along 
Hurricane and the Gulf Coast

43

the Gulf Coast – 3.5 times the number in 1950 – and their numbers are growing by nearly 7 

percent a year.17 From 1970 to 1994, the Gulf Coast averaged less than one hurricane landfall per season, and the East Coast averaged one hurricane landfall every fi ve years. Th is is 

in sharp contrast to the average of three U.S. hurricane landfalls during very active seasons. 

Unfortunately, decisions about land use, construction standards, etc. were based on an erroneous assumption, growing out of that period, that hurricanes would no longer aff ect the 

United States as frequently or as strongly as they had in earlier decades.18

Besides economic and population growth – including the swelling numbers of retirees 

drawn to warm-winter locales – engineering projects intended to prevent or reduce fl ood 

damage increased the appeal of the Gulf Coast. Here, as in the Southwest and the West 

Coast, “We are pushing toward the very areas where nature puts us most at risk from tropical storms, mudslides, and forest fi res,” Princeton University researcher Edward Tenner 

wrote in 1996. One of Tenner’s examples: “A big storm could leave 20 feet of water in 

downtown New Orleans and fl ood evacuation routes.”19

Ten years before Hurricane Katrina struck New Orleans, NOAA saw signs that the Atlantic 

Ocean had entered a 10 to 40-year cycle of intense hurricanes that would present an especially serious threat to the Gulf Coast.20 From 1970 through 1994, the United States enjoyed 

what meteorologists viewed as “normal” Atlantic hurricane seasons, a period of relatively 

Hurricanes Betsy, Camille, 

and Katrina 

Geography and Map Division, 

The Library of Congress
Chapter 3

44

mild activity that had produced few major hurricanes, Th at period averaged fi ve hurricanes 

annually and 1.5 major hurricanes.21

Since 1995, however, hurricane seasons have averaged 7.6 hurricanes each year and 3.6 major hurricanes, with reported increases in their destructive power.22 Historically, the number 

of major hurricanes and the number of Caribbean hurricanes tended to follow the multi-decade cycle, according to a 2001 analysis by a team of hurricane experts, who said: “Th e late 

1920s to the 1960s were very active, while both the 1900s and the 1970s through the early 

1990s were quiescent.” 23

New Orleans was not the only major U.S. population center that was in greater danger of a 

catastrophic storm. Analysis of historical data showed that two regions of the United States 

– the East Coast from South Carolina to Maine and the Gulf Coast from Florida to Texas 

– faced a much greater risk of catastrophic hurricanes and storm surges. 

Marking the beginning of a new multi-decade period of hurricanes activity involves extensive analysis of historical trends, conditions in the Atlantic and the atmosphere.24 Even so, 

there are no guarantees. Catastrophic hurricanes have occurred in years of normal or even 

below-normal hurricane activity. In 1972, Hurricane Agnes never got beyond Category 1 

strength, but still caused 122 deaths in the United States, with severe fl ooding in Virginia 

and the Carolinas.25 Hurricane Andrew, the most damaging hurricane in U.S. history before 

Katrina, formed during a season (and cycle, lasting until 1994) of below-normal activity.26

Between 1995 and 2000, however, the North Atlantic had the highest level of hurricanes 

on record, including several that threatened New Orleans.27 Among them was Hurricane 

Georges in 1998, a Category 3 storm that caused 602 deaths in the Caribbean, set a track for 

New Orleans, but turned toward Mississippi before making landfall. 28 By 2000, hurricane 

experts had concluded that the Atlantic was undergoing “multi-decadal conditions” that 

favored more major hurricanes. Scientists began calling for improvements in hurricane 

preparedness.29 Th e NWS was issuing annual Atlantic Hurricane Outlooks, long-range forecasts of hurricane activity and severity.30 Released each May before the June 1 start of the 

hurricane season, the Outlooks relied on a yardstick known as the Accumulated Cyclone 

Energy (ACE) Index.31

Th e agency’s 2003 Outlook predicted a 55 percent likelihood of above-normal hurricane 

activity, with an estimated range of two to four major hurricanes. However, the projected 

ACE value of the season had a staggering range: 110-180 percent of the median, which was 

much higher than 2002 and the 1971-1994 period.32 Two months later, the agency increased 

the probability for an above-normal hurricane season to 60 percent and projected that three 

to four major hurricanes would threaten the United States.33 Th e assessment was correct: By 

November, the Atlantic had spawned three major hurricanes, including Isabel, a storm that 

reached Category 5 strength before striking North Carolina as a Category 2.34

A year later, the Outlook for 2004 predicted a 50 percent chance of an above-normal hurricane season, with two to four major hurricanes and an ACE index in the range of 100-160 

percent. Th at year, four major storms roared through the Gulf, including Hurricane Ivan. 

Th is Category 5 storm produced at least 34 tornadoes and was the most destructive hurricane to strike the Florida Panhandle and Alabama coast in a hundred years.35

Th e NWS’s 2005 Outlook, issued in May, predicted yet another above-normal hurricane 

season with twice the usual number of major hurricanes.36 Th is time, the pre-season estimate called for three to fi ve major storms and made it clear that the odds of a catastrophic 

storm were increasing. “Th e main uncertainly in this outlook is not whether the season will 

be above normal, but how much above normal it will be,” the report said.37
Hurricane and the Gulf Coast

45

During the next 60 days, the Atlantic spawned seven tropical storms and two major hurricanes, Dennis and Emily.38 On August 2, the NWS issued an update of its 2005 Outlook 

that predicted a “95% to 100% chance” of an above-normal hurricane season and increased 

its estimated range from three to fi ve, to fi ve to seven storms. 39

Twenty-one days later, on August 23, Tropical Depression 12 developed about 175 nautical 

miles southeast of Nassau, in the Bahamas. Th e following day, it was designated Tropical 

Storm Katrina.40

1 Christopher Landsea et al., “Atlantic Basin Hurricanes: Indices of Climatic Changes,” Climatic Change 42:1, May 1999, 

pp. 89-129; Stanley B. Goldenberg et al., “Th e Recent Increase in Atlantic Hurricane Activity: Causes and Implications,” 

Science, July 20, 2001, pp. 475-467 [hereinaft er Goldenberg, “Th e Recent Increase in Atlantic Hurricane Activity”]; and 

Lloyd J. Shapiro and Stanley B. Goldenberg, “Atlantic Sea Surface Temperatures and Tropical Cyclone Formation,” Journal of Climate 11, 1997, pp. 578-590; National Aeronautics and Space Administration, Earth Observatory “Hurricanes: 

Th e Greatest Storms on Earth.” http://earthobservatory.nasa.gov/Library/Hurricanes/index.html. Accessed on Mar. 31, 

2006 [hereinaft er NASA, “Hurricanes: Th e Greatest Storms on Earth”] (“Hurricanes form over tropical waters (between 

8° and 20° latitude) in areas of high humidity, light winds, and warm sea surface temperatures (typically 26.5°C [80°F] or 

greater). Th ese conditions usually prevail in the summer and early fall months of the tropical North Atlantic and North 

Pacifi c Oceans and for this reason, hurricane ‘season’ in the northern hemisphere runs from June through November.”).

2 NASA, “Hurricanes: Th e Greatest Storms on Earth.” 

Hurricanes are sorted into categories on the Saffi r-Simpson Scale, named for the engineer and the meteorologist who 

developed it in the 1970s. Its fi ve categories are now the standard method for classifying hurricanes:

Category 1 2 3 4 5 

 Wind speed (mi/hr) 74–95 96–110 111–130 131–155 155+ 

 Storm surge (ft ) 4–5 6–8 9–12 13–18 18+

Damage Minimal Moderate Extensive Extreme Catastrophic 

3 National Oceanic and Atmospheric Administration, Hurricane Research Division, “When is Hurricane Season?” 

http://www.aoml.noaa.gov/hrd/tcfaq/G1.html. Accessed on Jan. 24, 2006 (“Th e Atlantic hurricane season is offi cially 

from 1 June to 30 November. Th ere is nothing magical in these dates, and hurricanes have occurred outside of these six 

months, but these dates were selected to encompass over 97% of tropical activity. Th e Atlantic basin shows a very peaked 

season from August through October, with 78% of the tropical storm days, 87% of the minor (Saffi r-Simpson Scale categories 1 and 2 – see Subject D1) hurricane days, and 96% of the major (Saffi r-Simpson categories 3, 4 and 5) hurricane 

days occurring then (Landsea 1993). Maximum activity is in early to mid September.”).

4 Technical Data Report: Southeast Louisiana Hurricane Preparedness Study, prepared by U.S. Army Corps of Engineers, 

New Orleans District for Federal Emergency Management Agency, Aug. 1994, p. 2–12 [hereinaft er Southeast Louisiana 

Hurricane Preparedness Study, Aug. 1994] (“Most hurricanes weaken aft er landfall because the central pressure increases 

and the radius of maximum winds tends to increase. Th e terrain of southern Louisiana is very low, fl at, and marshy and 

the transition to land from water is not abrupt.”).

5 See: National Weather Service, National Hurricane Center, Tropical Prediction Center. http://www.nhc.noaa.gov.

6 Southeast Louisiana Hurricane Preparedness Study, Aug. 1994, p. 2–2 (“A hurricane moving over the continental shelf 

produces a buildup of water at the coastline which is commonly referred to as storm surge. Storm surge is the increase 

in height of the surface of the sea due to the forces of an approaching hurricane. Storm surge normally occurs over a 

coastline for distances of 100 miles or more. Th e winds associated with a hurricane are the largest single component 

responsible for the buildup of storm surge within a basin. Th e wind blowing over the surface of the water exerts a horizontal force which induces a surface current in the general direction of the wind. Th e surface current, in turn, induces 

currents in subsurface water. Th is process of current creation continues to a depth which is determined by the depth of 

the water and by the intensity and forward motion of the hurricane. For example, a fast moving hurricane of moderate 

intensity may only induce currents to a depth of a hundred feet, whereas a slow moving hurricane of moderate intensity 

might induce currents to several hundred feet. Th ese horizontal currents are impeded by a sloping continental shelf as 

the hurricane approaches the coastline, thereby causing the water level to rise. A wide gently sloping continental shelf 

is particularly conducive to the formation of large storm surges. Th e amount of rise increases shoreward to a maximum 

level at, or some distance inland from the shoreline.”).

7 Louisiana Offi ce of Homeland Security and Emergency Preparedness and Louisiana State Hazard Mitigation Planning 

Committee, State of Louisiana Hazard Mitigation Plan, Apr. 15, 2005, p. I–46 [hereinaft er State of Louisiana Hazard 

Mitigation Plan, Apr. 15, 2005] (“In Louisiana, storm surges are large waves of Gulf waters that sweep across coastlines 

where a tropical storm makes landfall. Generally the more intense the storm, the greater the height of the storm surge; 

the higher the storm surge, the greater the damage to the coastline. Storm surges inundate coastal fl oodplains, wash out 

dunes, cause backwater fl ooding through coastal river mouths, generate large waves that run up and fl ood coastal beach-
Chapter 3

46

es, and can fl ood streets and buildings in coastal communities....Th e coastal bathymetry of southeastern Louisiana, with 

its low, fl at topography and land surface elevations that in many places dip below sea level, can experience storm surges 

up to 100 miles inland. Category 3 storms can bring depths up to 24 feet as far north as the City of New Orleans. Category 5 storms can produce depths as high as 36 feet. Furthermore, lakes along the coast, namely, Lake Maurepas, Lake 

Borgne, and Lake Pontchartrain, exacerbate the eff ects of coastal fl ooding because of wave eff ects that can regenerate 

over inland lakes. It is important to note that the map represents the cumulative storm surges for hundreds of modeled 

hypothetical hurricane tracks; no single hurricane event would produce the inundation pattern depicted on the map.”).

8 National Hurricane Center, Hurricane Preparedness, “Hurricane Preparedness Week.” http://www.nhc.noaa.gov/

HAW2/english/intro.shtml. Accessed on Jan. 16, 2006.

9 Ed Rappaport, National Hurricane Center, Preliminary Report: Hurricane Andrew, 16-28 August 1992, Dec. 10, 1993. 

http://www.nhc.noaa.gov/1992andrew.html. Accessed on Apr. 26, 2006 [hereinaft er Rappaport, Preliminary Report: 

Hurricane Andrew].

10 Brian Jarvinen, National Hurricane Center, Hurricane Preparedness, “Storm Surge.” http://www.nhc.noaa.gov/

HAW2/english/storm_surge.shtml. Accessed on Apr. 27, 2006.

11 Written Statement of Brig. Gen. David L. Johnson, U.S. Air Force (Ret.), Assistant Administrator for Weather Services, and Director, National Weather Service, National Oceanic and Atmospheric Administration, for the U.S. House 

of Representatives, Committee on Science, hearing on NOAA Hurricane Forecasting, Oct. 7, 2005, p. 3 (“Th e mission of 

the National Weather Service (NWS) is to issue weather, water and climate forecasts and warnings for the protection 

of life and property and the enhancement of the national economy. Nowhere is that more evident than in the hurricane 

program.”). Source: Written Statement of Brig. Gen. Johnson, House Committee on Science hearing, Oct. 7, 2005, p.1. 

In 1943, aircraft reconnaissance of the hurricanes began. In 1959, land-based weather radars were placed at Lake Charles 

and Slidell, Louisiana and Pensacola, Florida. In the 1960s scientists gained the ability to observe tropical storm behavior 

through the use of satellite photography. Source: Southeast Louisiana Hurricane Preparedness Study, Aug. 1994, p. 1-9.

12 Written Statement of Brig. Gen. Johnson, House Committee on Science hearing, Oct. 7, 2005, p. 4 (“Following Hurricane Camille in 1969, NOAA established a group that developed and implemented a storm surge model called SLOSH 

(Sea, Lake, and Overland Surges from Hurricanes) Th e SLOSH model calculates storm surge heights resulting either 

from historical, hypothetical or actual hurricanes. SLOSH incorporates bathymetry and topography, including bay and 

river confi gurations, roads, levees, and other physical features that can modify the storm surge fl ow pattern.”). See also:

Southeast Louisiana Hurricane Preparedness Study, Aug. 1994, p. 2-6 (“In addition to furnishing surge heights for the 

open coast, the SLOSH model has the added capability to compute the routing of storm surge into bays, estuaries, or 

coastal river basins as well as calculating surge heights for overland locations. Signifi cant natural and man-made barriers 

are represented in the model and their eff ects simulated in the calculations of surge heights within a basin.”); State of 

Louisiana Hazard Mitigation Plan, Apr. 15, 2005, p. I–46 (“Storm surge areas can be mapped by the probability of storm 

surge occurrences using Sea, Lake and Overland Surges from Hurricanes modeling (referred to as SLOSH modeling)...

SLOSH models represent the storm surge of hundreds of simulated hurricanes, taking into account storm wind intensities, forward speeds, directions of motion, and radius of maximum winds.”).

13 Testimony of Robert Sheets, Ph.D., Director, National Hurricane Center, before the U.S. Senate, Committee on Governmental Aff airs, hearing on Rebuilding FEMA: Preparing for the Next Disaster, May 18, 1993, p. 45.

14 Written Statement of Max Mayfi eld, Ph.D., Director, National Hurricane Center, for the U.S. House, Select Bipartisan 

Committee to Investigate the Preparation for and Response to Hurricane Katrina, hearing on Predicting Hurricanes: 

What We Knew About Katrina and When, Sept. 22, 2005, p. 5. For instance, the NWS used reconnaissance aircraft 

equipped with Stepped Frequency Microwave Radiometer (SFMR) that collects data about hurricane structure, surface 

wind and rain rate. See also: Written Statement of Brig. Gen. Johnson, House Committee on Science hearing, Oct. 7, 

2005, p. 3 NWS also uses hurricane monitoring buoys deployed in the Caribbean.

15 Committee staff interview of Max Mayfi eld, Ph.D., Director, National Hurricane Center, conducted on Jan. 27, 2006, 

transcript pp. 29-40.

16 For a detailed description of topography and economic development of the Louisiana Gulf Coast, see: Southeast Louisiana Hurricane Preparedness Study, Aug. 1994, pp. 1–2 through 1–5.

17 U.S Census Bureau, U.S. Census Bureau News, Newsroom “Almost 10 Million Gulf Coast Residents Bracing for Hurricane Dennis,” press release, July 8, 2005. http://www.census.gov/PressRelease/www/releases/archives/hurricanes_tropical_storms/005345.html. Accessed on Jan. 27, 2006.

18 National Oceanic and Atmospheric Administration, “NOAA Attributes Recent Increase in Hurricane Activity to 

Naturally Occurring Multi-Decadal Climate Variability,” NOAA Magazine, Nov. 29, 2005. http://www.magazine.noaa.

gov/stories/mag184.htm. Accessed on Mar. 8, 2006 [hereinaft er NOAA, “NOAA Attributes Recent Increase in Hurricane Activity to Naturally Occurring Multi-Decadal Climate Variability”].

19 Edward Tenner, Why Th ings Bite Back: Technology and the Revenge of Unintended Consequences, New York: Knopf, 

1996, pp. 93-94.

20 Goldenberg, “Th e Recent Increase in Atlantic Hurricane Activity” pp. 474-479 (“Th e years 1995 to 2000 experienced 

the highest level of North Atlantic hurricane activity in the reliable record. Compared with the generally low activity of 

the previous 24 years (1971 to 1994), the past 6 years have seen a doubling of overall activity for the whole basin, a 2.5-

fold increase in major hurricanes ... fi ve-fold increase in hurricanes aff ecting the Caribbean.”).

21 National Weather Service, Climate Prediction Center, “Background Information: Th e North Atlantic Hurricane 
Hurricane and the Gulf Coast

47

Season.” http://www.cpc.ncep.noaa.gov/products/outlooks/background_information.shtm. Accessed on Apr. 6, 2006. 

(“An average hurricane season features ten tropical storms (maximum sustained winds between 39-73 mph), of which 

an average of six become hurricanes (maximum sustained winds of at least 74 mph) and two become major hurricanes 

(maximum sustained winds exceeding 110 mph, categories 3-5 on the Saffi r-Simpson scale).”).

22 National Oceanic and Atmospheric Administration, National Climatic Data Center, National Environmental Satellite, Data, and Information Service, “Climate of 2005, Atlantic Hurricane Season.” http://www.ncdc.noaa.gov/oa/climate/research/2005/hurricanes05.html. Accessed on Apr. 30, 2006. (“Tropical cyclone activity in the Atlantic basin has 

been above normal since 1995. Th is has been largely in response to the active phase of the multi-decadal signal. Th e 

average number of named storms since 1995 has been 13, compared to 8.6 during the preceding 25 years during which 

time the multi-decadal signal was in an inactive phase. An average of 7.7 hurricanes and 3.6 major hurricanes since 1995 

compares to 5 hurricanes and 1.5 major hurricanes from 1970-1994. Characteristics of an active multi-decadal signal in 

the Atlantic include: warmer SSTs in the tropical Atlantic region, an amplifi ed sub-tropical ridge at upper levels across 

the central and eastern North Atlantic, reduced vertical wind shear in the deep tropics over the central North Atlantic, and an African Easterly Jet (AEJ) that is favorable for promoting the development and intensifi cation of tropical 

disturbances moving westward off the coast of Africa. Recent studies also indicate that in addition to this multi-decadal 

oscillation the destructive power of hurricanes has generally increased since the mid-1970s, when the period of the most 

rapid increase in global ocean and land temperatures began.”).

23 Goldenberg, “Th e Recent Increase in Atlantic Hurricane Activity,” pp. 476-477 (“Th e Caribbean Sea has shown 

dramatic changes in hurricane activity – averaging 1.7 occurrences per year during the warm periods compared with 

only 0.5 per year during the cold period (34). Th e current warm period has produced an average of 2.5 occurrences per 

year with an unprecedented (since 1944) six hurricanes in the region during 1996. ... Th is means that during the next 10 

to 40 years or so, most of the Atlantic hurricane seasons are likely to have above average activity, with many hyperactive, some around average, and only a few below average. Furthermore, consistent with experience since the active phase 

began in 1995, there would be a continuation of signifi cantly increased numbers of hurricanes (and major hurricanes) 

aff ecting the Caribbean Sea and basin-wide numbers of major hurricanes.”).

24 Goldenberg, “Th e Recent Increase in Atlantic Hurricane Activity,” pp. 474-479 (“Th e greater activity results from 

simultaneous increases in North Atlantic sea-surface temperatures and decreases in vertical wind shear.”). See also:

NOAA, “NOAA Attributes Recent Increase in Hurricane Activity to Naturally Occurring Multi-Decadal Climate 

Variability” (“Th is era has been unfolding in the Atlantic since 1995, and is expected to continue for the next decade or 

perhaps longer. NOAA attributes this increased activity to natural occurring cycles in tropical climate patterns near the 

equator. Th ese cycles, called ‘the tropical multi-decadal signal,’ typically last several decades (20 to 30 years or even longer). As a result, the North Atlantic experiences alternating decades long (20 to 30 year periods or even longer) of above 

normal or below normal hurricane seasons.”).

25 National Oceanic and Atmospheric Administration, NOAA Coastal Services Center, “Hurricane History.” http://

www.nhc.noaa.gov/HAW2/english/history.shtml. Accessed on Apr. 16, 2006. Agnes was barely a hurricane at landfall 

in Florida, and the eff ects of winds and storm surges were relatively minor. Th e major impact was over the northeastern 

United States, where Agnes combined with the non-tropical low to produce widespread rains of 6 to 12 inches with local 

amounts of 14 to 19 inches. Th ese rains produced widespread severe fl ooding from Virginia northward to New York, 

with other fl ooding occurring over the western portions of the Carolinas. Agnes caused 122 deaths in the United States. 

Nine of these were in Florida (mainly from severe thunderstorms) while the remainder were associated with the fl ooding. Th e storm was responsible for $2.1 billion in damage in the United States, the vast majority of which came from the 

fl ooding. Agnes also aff ected western Cuba, where seven additional deaths occurred.

26 Rappaport, Preliminary Report: Hurricane Andrew (“Andrew was a small and ferocious Cape Verde hurricane that 

wrought unprecedented economic devastation along a path through the northwestern Bahamas, the southern Florida 

peninsula, and south-central Louisiana. Damage in the United States is estimated to be near 25 billion, making Andrew 

the most expensive natural disaster in U.S. history.1

 Th e tropical cyclone struck southern Dade County, Florida, especially hard, with violent winds and storm surges characteristic of a category 4 hurricane (see addendum on upgrade 

to category 5) on the Saffi r/Simpson Hurricane Scale, and with a central pressure (922 mb) that is the third lowest this 

century for a hurricane at landfall in the United States. In Dade County alone, the forces of Andrew resulted in 15 deaths 

and up to one-quarter million people left temporarily homeless. An additional 25 lives were lost in Dade County from 

the indirect eff ects of Andrew. Th e direct loss of life seems remarkably low considering the destruction caused by this 

hurricane.”).

27 Goldenberg, “Th e Recent Increase in Atlantic Hurricane Activity,” pp. 474-479.

28 John L. Guiney, National Hurricane Center, Preliminary Report: Hurricane George, 15 September – 01 October 1998, 

Jan. 5, 1999. http://www.nhc.noaa.gov/1998georges.html. Accessed on Apr. 26, 2006. (“Georges (pronounced Zhorzh) 

was the second deadliest and second strongest hurricane within the Atlantic basin during the 1998 season. Its 17 day 

journey resulted in seven landfalls, extending from the northeastern Caribbean to the coast of Mississippi, and 602 fatalities – mainly in the Dominican Republic and Haiti.”).

29 Goldenberg, “Th e Recent Increase in Atlantic Hurricane Activity” p. 474 (“Th e years 1995 to 2000 experienced the highest level of North Atlantic hurricane activity in the reliable record. Compared with the generally low activity of the previous

24 years (1971 to 1994), the past 6 years have seen a doubling of overall activity for the whole basin, a 2.5-fold increase in 

major hurricanes (≥50 meters per second), and a twofold increase in hurricanes aff ecting the Caribbean. Th e greater activity results from simultaneous increases in North Atlantic sea-surface temperatures and decreases in vertical wind shear. 

Because these changes exhibit a multidecadal time scale, the present high level of hurricane activity is likely to persist for an 

additional ~ 10 to 40 years. Th e shift in climate calls for a reevaluation of preparedness and mitigation strategies.”).
Chapter 3

48

30 See: National Weather Service, Climate Prediction Center, “August 2004 Update to Atlantic Hurricane Season Outlook,” Aug. 10, 2004. http://www.cpc.noaa.gov/products/outlooks/hurricane2004/August/hurricane.html.

31 National Oceanic and Atmospheric Administration, National Climatic Data Center, “Hurricane Katrina A Climatological Perspective,” Oct. 2005, p. 23 (”Th e Accumulated Cyclone Energy Index is one method to describe trends in 

tropical cyclone activity. Th is index is a combination of the tropical cyclone’s duration in a particular ocean basin, along 

with the strength of each storm.”).

32 National Weather Service, Climate Prediction Center, “NOAA: 2003 Atlantic Hurricane Outlook,” May 19, 2003. 

http://www.cpc.noaa.gov/products/outlooks/hurricane2003/May/hurricane.html. Accessed on April 5, 2006 (“Th is 

expected activity is considerably more than the four hurricanes and ACE value of 74% of the median observed during 

2002. It is also much larger than the seasonal average of fi ve hurricanes and ACE value of 75% of the median observed 

during the relatively quiet period 1970-1994.”).

33 National Weather Service, Climate Prediction Center, “NOAA: 2003 Atlantic Hurricane Outlook Update,” Aug, 7, 

2003. http://www.cpc.noaa.gov/products/outlooks/hurricane2003/August/hurricane.html. Accessed on Apr. 4, 2006.

34 Isabel is considered to be one of the most signifi cant tropical cyclones to aff ect portions of northeastern North Carolina and east-central Virginia since Hurricane Hazel in 1954 and the Chesapeake-Potomac Hurricane of 1933. Jack Bevin 

and Hugh Cobb, National Oceanic and Atmospheric Administration, “Tropical Cyclone Report for Hurricane Isabel 6 

– 19 September 2003.” Jan. 16, 2004. http://www.nhc.noaa.gov/2003isabel.shtml. Accessed on Apr. 14, 2006. 

35 Gerald Bell, et al., “Th e 2004 North Atlantic Hurricane Season: A Climate Perspective,” pp. 1-4. http://www.cpc.

ncep.noaa.gov/products/expert_assessment/hurrsummary_2004.pdf#search=’Th e%202004%20North%20Atlantic%20

Hurricane%20Season%3A%20A%20Climate%20Perspective’. Accessed on Apr. 26, 2006 (“Th e 2004 Atlantic hurricane 

season had well above-normal activity, with 15 named storms, 9 hurricanes (H), and 6 major hurricanes [MH, defi ned as 

categories 3-5 on the Saffi r-Simpson scale, Simpson (1974)]. Nine of these systems struck the continental United States, 

three as tropical storms (Bonnie, Hermine, and Matthew) and six as hurricanes (Alex, Charley, Frances, Gaston, Ivan, 

and Jeanne). Th ree of the hurricanes (Charley, Ivan, and Jeanne) hit as major hurricanes... MH Ivan, the strongest of the 

2004 hurricanes, eventually made landfall in Alabama and produced the largest storm total ACE value (70.4 x 104 kt2) in 

the reliable record.”).

36 National Weather Service, Climate Prediction Center, “NOAA: 2005 Atlantic Hurricane Outlook,” May 16, 2005. 

http://www.cpc.noaa.gov/products/outlooks/hurricane2005/May/hurricane.html. Accessed on Apr. 4, 2006; Written 

Statement of Max Mayfi eld, Ph.D., Director, National Hurricane Center, for the U.S. Senate, Committee on Commerce, 

Science, and Transportation, hearing on Th e Life Saving Role of Accurate Hurricane Prediction, Sept. 20, 2005, p. 6 (“Th e 

natural cycles are quite large with on average 3-4 major hurricanes a year in active periods and only about 1-2 major 

hurricanes annually during quiet periods, with each period lasting 25-40 years.”).

37 National Weather Service, Climate Prediction Center, “NOAA: 2005 Atlantic Hurricane Outlook,” May 16, 2005. 

http://www.cpc.noaa.gov/products/outlooks/hurricane2005/May/hurricane.html. Accessed on Apr. 4, 2006.

38 National Weather Service, Climate Prediction Center, “NOAA: August 2005 Update to Atlantic Hurricane Season 

Outlook,” Aug. 2, 2005. http://www.cpc.noaa.gov/products/outlooks/hurricane2005/August/hurricane.html. Accessed 

on Apr. 4, 2006 (“Th e predicted seasonal totals include the considerable activity that has already occurred prior to this 

update (7 tropical storms and 2 major hurricanes)...Of particular relevance to this outlook is that two July tropical systems, Major Hurricanes Dennis and Emily, formed over the eastern Caribbean Sea and over the central tropical Atlantic 

(near 10°N), respectively. It is rare for hurricanes to develop in these regions during July because the wind patterns are 

normally so unfavorable.”).

39 National Oceanic and Atmospheric Administration, “August 2005 Update to Atlantic Hurricane Season Outlook,” 

Aug. 2, 2005. http://www.cpc.noaa.gov/products/outlooks/hurricane2005/August/hurricane.html. Accessed on Apr. 4, 

2006 (“Th e updated outlook calls for an extremely active season, with an expected seasonal total of 18-21 tropical storms 

(mean is 10), with 9-11 becoming hurricanes (mean is 6), and 5-7 of these becoming major hurricanes (mean is 2-3). Th e 

likely range of the ACE index for the season as a whole is 180%-270% of the median. Th e predicted seasonal totals include the considerable activity that has already occurred prior to this update (7 tropical storms and 2 major hurricanes). 

Th erefore, for the remainder of the season, we expect an additional 11-14 tropical storms, with 7-9 becoming hurricanes, 

and 3-5 of these becoming major hurricanes. Th e expected ACE range during August-November is 110%-200% of the 

median. Th ese very high levels of activity are comparable to those seen during August-November 2003 and 2004.”).

40 Richard D. Knabb, Jamie R. Rhome, and Daniel P. Brown, National Hurricane Center, “Tropical Cyclone Report 

Hurricane Katrina 23-30 August 2005,” Dec. 20, 2005, p. 1. http://www.nhc.noaa.gov/pdf/TCR-AL122005_Katrina.

pdf#search=’Tropical%20Cyclone%20Report%20Hurricane%20Katrina’. Accessed on Apr. 26, 2006.
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