Mitigation Assessment Team Report 
Hurricane Katrina in the Gulf Coast
Building Performance Observations, Recommendations, and Technical Guidance
FEMA 549 / July 2006

Chapter 1. Introduction 

On September 26, 2005, the Mitigation Division of the Department of Homeland 
Securitys (DHSs) Federal Emergency Management Agency (FEMA) deployed a 
Mitigation Assessment Team (MAT) to the States of Alabama, Louisiana, and 
Mississippi to assess damage caused by Hurricane Katrina. This report presents 
the MATs observations, conclusions, and recommendations in response to those 
field investigations.

This chapter provides an introduction, a discussion of the event, historical 
information, and background on the MAT process. Floodplain management 
regulations and the building codes and standards that affect construction in 
Alabama, Louisiana, and Mississippi are discussed in Chapter 2. Chapter 3 
provides a basic assessment and characterization of the observed flood and wind 
effects. Structural systems performance in residential and commercial buildings 
is detailed in Chapter 4. Chapter 5 presents an assessment of building envelope 
performance and Chapter 6 discusses damage to historic buildings. Chapter 7 
presents damage to, and functional loss of, critical and essential facilities, 
and Chapter 8 discusses the short-term and long-duration flood impacts in the 
New Orleans area. Chapter 9 documents observed hazard mitigation successes and 
best practices. Chapters 10 and 11 present the conclusions and recommendations, 
respectively, intended to help guide the reconstruction for hurricane-resistant 
communities in Alabama, Louisiana, and Mississippi, and other hurricane-prone 
regions impacted by future hurricanes. In addition, the following appendices are 
presented herein:

- Appendix A contains the references for the report.
- Appendix B is a list of acknowledgments.
- Appendix C defines the acronyms and abbreviations used in the report.
- Appendix D contains a glossary of terms used in the report.
- Appendix E contains the Hurricane Katrina Recovery Advisories.
* Reconstruction Guidance Using Hurricane Katrina Surge Inundation and Advisory 
Base Flood Elevations
* Initial Restoration for Flooded Buildings
* Design and Construction in Coastal A Zones 
* The ABC's of Returning to Flooded Buildings 
* Attachment of Brick Veneer in High-Wind Regions
* Attachment of Rooftop Equipment in High-Wind Regions
* Rooftop Attachment of Lightning Protection Systems in High-Wind Regions
* Designing for Flood Levels Above the BFE- Appendix F presents high water marks 
reported for the storm.
- Appendix G contains a copy of FEMA Procedure Memorandum 34 - Interim Guidance 
for Studies Including Levees, dated August 22, 2005.
- Appendix H contains a description of Continuity of Operations (COOP) Planning 
and Environmental Issues for Infrastructure.
- I presents a description of sampling and analytical methods of flood-damaged 
buildings.  
- Appendix J describes pre- and post-disaster mitigation of historic buildings.
- Appendix K contains a list of FEMA Regional Offices.

1.1 Hurricane Katrina  The Event

Hurricane Katrina was one of the strongest and most destructive storms to impact 
the coast of the United States during the past 100 years. The hurricane made its 
first landfall on August 25, 2005, on the southeast coast of Florida as a 
Category 1 hurricane; the storm then crossed south Florida and moved into the 
Gulf, where it gained strength to a Category 5 hurricane, before weakening and 
making its second landfall in southeast Louisiana near Buras as a strong 
Category 3 hurricane. After coming ashore in Louisiana, Katrina continued to 
move northward, pushing storm surge into coastal areas of Alabama, Louisiana, 
and Mississippi, and, after crossing over Breton Sound, Katrina finally made a 
third landfall as a Category 3 storm near Pearlington, Mississippi, along the 
Louisiana/Mississippi border. Figure 1-1 shows the path of Hurricane Katrina as 
it moved over Louisiana and Mississippi. Katrina caused widespread devastation 
along the Gulf Coast, with southeast Louisiana and the coasts of Alabama and 
Mississippi bearing the brunt of the catastrophic damage.

[Begin text box]
THE SIGNIFICANCE OF HURRICANE KATRINA 
Hurricane Katrina was the most severe hurricane to strike the 
Louisiana/Mississippi Gulf Coast since Hurricane Camille in 1969 and the most 
significant hurricane to strike the New Orleans area since Hurricane Betsy in 
1965. The significance of Katrina and its effects are summarized below:

- Katrina significantly exceeded the Base Flood Elevations (BFEs) by as much as 
15 feet along parts of the Louisiana and Mississippi Gulf Coast. Flooding 
extended well beyond the inland limits of the Special Flood Hazard Area (SFHA), 
and the highest storm surge in U.S. history was recorded on the Mississippi 
coast. 
- The American Red Cross estimated that Katrina destroyed over 300,000 single 
family homes throughout Louisiana and Mississippi. 

- Coastal flood impacts covered a wide area, with severe flood damage extending 
along coastal Alabama and totally destroying over 100 houses on Dauphin Island. 

- Levee failures led to severe flood damage throughout the City of New Orleans 
and surrounding areas of Plaquemines and St. Bernard Parishes. Hundreds of 
thousands of people were displaced from the damage caused by the flooding. 

- Katrinas wind speeds were estimated to be at the design level in only a few 
areas and were less than the current code-specified speeds (per the 2000/2003 
International Building Code [IBC] and the International Residential Code [IRC]) 
in most areas. These codes use a design wind speed map developed for the 1998 
and 2002 editions of the American Society of Civil Engineers (ASCE) 7. 

- Wind damage to both commercial and residential buildings was widespread 
through the southern portions of Louisiana and Mississippi. 

- In general, buildings functioning as critical and essential facilities did not 
perform well, and experienced significant wind and flood damage (with damages 
similar in nature to their commercial counterparts). Operation of many critical 
and essential facilities was hampered or shut down as a result of storm-induced 
damage or isolation due to coastal flooding. 
[End text box]

Figure 1-1. A map showing Hurricane Katrinas path through Louisiana and 
Mississippi (BASED ON HURRICANE STORM TRACK DATA FROM THE NATIONAL HURRICANE 
Center)

Katrinas storm surge caused failure of the levee system that protects New 
Orleans from Lake Pontchartrain and, subsequently, an estimated 80 percent of 
the city was flooded. This and other major damage to the coastal regions of 
Alabama, Louisiana, and Mississippi made Katrina the most destructive natural 
disaster in the history of the United States. 

The estimated death toll is over 1,700, with approximately 1,500 of those deaths 
occurring in Louisiana and approximately 230 in Mississippi. [Footnote 1] Other 
deaths attributed both directly and indirectly to Katrina were reported in 
Florida, Alabama, Georgia, Kentucky, and Ohio. Hurricane Katrina ranks as the 
third deadliest hurricane in the United States, surpassed only by the Texas 
Hurricane at Galveston in 1900, where 6,000 lives were lost, and the Florida 
Hurricane in 1928 where 2,500 lives were lost at Lake Okeechobee. 

Footnote 1. The original toll of 1,067 issued by the Louisiana Department of 
Health and Hospitals included at least 14 who died prior to Katrina, and some 
people who were elderly or terminally ill and died outside of New Orleans after 
evacuation, possibly due to stress, as reported by The Times-Picayune on 
November 2, 2005 <http://www.nola.com/search/index.ssf?/base/library-
89/113091548771970.xml?nola>.

1.1.1 Hurricane Katrina Economic Loss Summary

Estimated total economic losses from Hurricane Katrina are in excess of $125 
billion and insured losses are $40.6 billion, [footnote 2] which tops Hurricane 
Andrews $26.5 billion loss, Hurricane Charleys $15 billion loss, Hurricane 
Ivans $14.2 billion loss, Hurricane Frances $8.9 billion loss, and Hurricane 
Hugos $7 billion loss, [footnote 3] making Katrina the most expensive natural 
disaster in U.S. history. As of April 2006, the number of flood insurance claims 
exceeded 210,000 and totaled $17 billion, covering Alabama, Florida, Louisiana, 
and Mississippi, with over 175,000 of those claims coming from Louisiana. 
Preliminary estimates indicate that Hurricane Katrina resulted in the following:

Footnote 2. Insurance Information Institute
Footnote 3. Estimates, not adjusted for inflation, as reported by 
NOAA/AOML/Hurricane Research Division, Miami, FL 
<http://www.nhc.noaa.gov/pastcost.shtml>.

- $5.5 billion in damage to infrastructure, including roads and bridges
- 300,000 to 350,000 vehicles destroyed and approximately 2,400 ships and 
vessels wrecked
- 450,000 displaced people
- 800,000 Louisiana citizens requesting assistance from various Federal and 
State relief programs and agencies
The Small Business Administration reported that requests for $229 million in 
home and small business loans have been submitted. The State of Mississippi and 
FEMA counted the following destroyed or damaged buildings: primary homes -
157,914; multi-unit homes 20,883; rental units 42,187; and public housing 
units 27,001.
Table 1-1 summarizes the housing damage from Hurricane Katrina as determined by 
the American Red Cross.

[Begin Table]
Table 1-1. Katrina Housing Damage Summary

Location: Alabama
Dwelling Type: Single-Family
Destroyed: 363
Major: 966
Minor: 345
 
Dwelling Type: Manufactured
Destroyed: none 
Major: 1
Minor: 26
 
Dwelling Type: Apartment
Destroyed: none 
Major: none 
Minor: none 
 
Dwelling Type: Subtotal
Destroyed: 363
Major: 967
Minor: 371
 
Location: Louisiana
Dwelling Type: Single-Family
Destroyed: 241,524
Major: 38,350
Minor: 40,066
 
Dwelling Type: Manufactured
Destroyed: 1,552
Major: 1,146
Minor: 1,855
 
Dwelling Type: Apartment
Destroyed: 40,762
Major: 33,676
Minor: 27,842
 
Dwelling Type: Subtotal
Destroyed: 283,838
Major: 73,172
Minor: 69,763
 
Location: Mississippi
Dwelling Type: Single-Family
Destroyed: 68,466
Major: 62,981
Minor: 95,468
 
Dwelling Type: Manufactured
Destroyed: 263
Major: 2,241
Minor: 4,811
 
Dwelling Type: Apartment*
Destroyed: none 
Major: none 
Minor: none
 
Dwelling Type: Subtotal
Destroyed: 68,729
Major: 65,237
Minor: 100,318
 
Hurricane Katrina TOTALS
Dwelling Type: Single-Family
Destroyed: 310,353
Major: 102,297
Minor: 135,879
 
Dwelling Type: Manufactured
Destroyed: 1,815
Major: 3,388
Minor: 6,692
 
Dwelling Type: Apartment
Destroyed: 40,762
Major: 33,691
Minor: 27,881
 
Dwelling Type: Total
Destroyed: 352,930
Major: 139,376
Minor: 170,452
 
(SOURCES: AMERICAN RED CROSS, NATIONAL ASSOCIATION OF HOME BUILDERS, 10/05 
<http://www.redcross.org>, <http://www.nahb.org>.)
* Data incomplete.
[End Table]

Officials estimate that, in Mobile County, 80 percent of the homes in Bayou La 
Batre were uninhabitable as the result of flooding; on Dauphin Island, a third 
of the homes on the western side of the island were destroyed and another third 
were significantly damaged. The worst damages in Baldwin County were along 
Mobile Bay south of Fairhope and along the Ft. Morgan Peninsula.
 
Early in 2006, the Alabama Emergency Management Agency estimated that more than 
37,000 individuals sought service from Disaster Recovery Centers, and nearly 
7,000 individuals were still living in interim housing facilities.

1.1.1.1 Hurricane Categories

Hurricanes are categorized according to their relative strength as measured by 
wind speed and minimum central pressure. The Saffir-Simpson Scale, presented as 
Table 1-2, is the standard for categorizing hurricanes and consists of five 
separate categories. The National Hurricane Center (NHC) reserves the term 
major hurricane for hurricanes that reach maximum 1-minute sustained surface 
winds of at least 111 miles per hour (mph) over open water. Therefore, Category 
3, 4, and 5 hurricanes are all considered major hurricanes.

[Begin Table]
Table 1-2. Saffir-Simpson Hurricane Scale Wind Speeds and Pressures

Strength: Category 1
Sustained Wind Speed (mph)*: 74-95
Gust Wind Speed (mph)**: 89-116
Pressure (millibars): >980
 
Strength: Category 2
Sustained Wind Speed (mph)*: 96-110
Gust Wind Speed (mph)**: 117-134
Pressure (millibars): 965-979
 Strength: Category 3
Sustained Wind Speed (mph)*: 111-130
Gust Wind Speed (mph)**: 135-159
Pressure (millibars): 945-964
 
Strength: Category 4
Sustained Wind Speed (mph)*: 131-155
Gust Wind Speed (mph)**: 160-189
Pressure (millibars): 920-944
 
Strength: Category 5
Sustained Wind Speed (mph)*: >155
Gust Wind Speed (mph)**: >189
Pressure (millibars): <920
 
* 1-minute sustained over open water
** 3-second gust over open water
[End Table] 

1.1.1.2 Timeline and History of the Hurricane [footnote 4]

Footnote 4. All wind speeds provided in this section are estimated wind speed 
values as provided by the National Hurricane Center.

Hurricane Katrina began as Tropical Depression Twelve, which formed over the 
Bahamas on August 23, 2005. On August 24, the storm strengthened and became 
known as Tropical Storm Katrina, the 11th named storm of the 2005 hurricane 
season. The storm then traveled northwest from the Bahamas. 

A few hours before making landfall in Florida on August 25, Tropical Storm 
Katrina was upgraded to Hurricane Katrina (Category 1, 74 mph winds). Katrina 
made landfall around 6:30 p.m. Eastern Daylight Time (EDT) with approximately 80 
mph, 1-minute sustained winds on the Dade-Broward County line between Hallandale 
Beach and North Miami Beach, Florida. Port Everglades reported wind gusts to 92 
mph. During its initial landfall in southern Florida, Katrina generated over 5 
inches of rainfall across a large area of southeastern Florida. An analysis by 
the National Oceanic and Atmospheric Administrations (NOAAs) Climate 
Prediction Center shows that parts of the region received heavy rainfall, over 
15 inches in some locations, which caused localized flooding. Katrina tracked 
southwest through the Everglades National Park and exited the state near the 
southern tip of Florida, as shown in Figure 1-2.

Figure 1-2. A map showing Hurricane Katrinas path and the categories it was 
along that path. (BASED ON 
http://cimss.ssec.wisc.edu/tropic/archive/2005/storms/katrina/katrina.html)

Katrina weakened as it passed over land on August 26, and again became a 
tropical storm before it entered the Gulf of Mexico. However, once over the 
Gulf, Katrina began regaining strength and, on August 28, reached Category 5 
hurricane status with sustained winds of 175 mph (gusts of 215 mph) and a 
central minimum pressure of 902 millibars (mb). [Footnote 5.] Later in the 2005 
hurricane season, Hurricanes Rita and Wilma developed with minimum pressures of 
897 mb and 882 mb, respectively. As a result, Katrina became the sixth most 
intense Atlantic Basin hurricane on record (Rita is now the third and Wilma 
ranks as the first). Katrinas rapid intensification was due in part to its 
movement over the warm Gulf waters. 

Footnote 5. Central pressure measurements are from the National Hurricane 
Centers Tropical Cyclone Report for Hurricane Katrina, dated December 20, 2005

At 6:10 a.m. Central Daylight Time (CDT) on August 29, Hurricane Katrina made 
landfall for the second time, near Buras, Louisiana, in Plaquemines Parish. 
According to the National Climatic Data Center (NCDC), Hurricane Katrina had 1-
minute sustained winds estimated at 127 mph upon landfall, and a minimum central 
pressure of 920 mb, making it the third lowest landfall pressure on record for 
the U.S., and placing it as a strong Category 3 hurricane on the Saffir-Simpson 
scale. After making landfall, Katrina moved northward up the Louisiana coast, 
subjecting much of Plaquemines and St. Bernard Parishes, as well as Slidell in 
St. Tammany Parish, to the damaging effects of its storm surge and strong winds. 

After passing New Orleans, Hurricane Katrina moved across the open waters of 
Breton Sound and the western edge of the Mississippi Sound and made landfall at 
10:00 a.m. CDT for a third time near Pearlington, Mississippi, located along the 
Louisiana/Mississippi border. At its third landfall, Katrina was a Category 3 
hurricane with 120-mph, 1-minute sustained winds. After making landfall and 
traveling more than 150 miles inland and reaching Jackson, Mississippi, the 
storm weakened, losing its hurricane strength, with sustained wind speeds 
dropping below 74 mph. Katrina kept moving northward, affecting weather in the 
central United States, until it was absorbed by a frontal boundary near 
southeast Quebec and northern New Brunswick, Canada, on August 31.

One of the key factors of this storm was its strength 24 hours before landfall 
when it was a large Category 5 hurricane with a minimum central pressure of 902 
mb. Although the storm weakened from a powerful Category 5 storm to a Category 3 
storm just before making landfall in Louisiana and Mississippi, the storm surge 
appears to have maintained a level associated with a Category 5 hurricane. The 
surge generated by the storm could not dissipate as rapidly as the wind speeds 
decreased, and the shallow depth of the offshore shelf and shape of the 
shoreline contributed to the high surge elevations. Storm surge pounded the 
coastline from southeast Louisiana to the Florida panhandle, with the 
Mississippi coastline experiencing the highest storm surges on record. 

After landfall, the eye traveled almost 100 miles across the Louisiana Delta 
before reaching the Mississippi coastline. However, the highest wind areas 
remained largely east of the delta over open water, with little reduction in 
velocity before reaching the Mississippi coastline.

Katrina was a wide storm, affecting a large area and pushing record storm surge 
onshore in its northeastern quadrant along the Alabama and Mississippi 
coastlines. Typically, surge elevations exceeded 23 feet North American Vertical 
Datum of 1988 (NAVD 88) throughout much of the Mississippi coastline, from 
Waveland east to Long Beach. The highest recorded surge and wave height 
elevation was 34.9 feet (NAVD 88). 

Although the eye of Hurricane Katrina did not directly hit New Orleans, 
catastrophic destruction occurred throughout the southeast portion of Louisiana. 
As the eye of the storm moved farther inland to the northeast of New Orleans 
later in the morning of August 29, winds began to blow from the north. With 
surge levels already high in Lakes Pontchartrain and Borgne, additional pressure 
from the strong north winds was put on the levee system protecting New Orleans. 
The levees/floodwalls of the canals that normally channel water from the low-
lying areas of the city (some below sea level) to pumping stations located along 
Lake Pontchartrain began to fail, allowing water to inundate large portions of 
the New Orleans area. Based on early investigations by the U.S. Army Corps of 
Engineers (USACE) Interagency Performance Task Force (USACE, 2006), there were 
three major levee breaches and a number of secondary breaches on Monday, August 
29, 2005. The major breaches were located along the Industrial Canal in the St. 
Claude Avenue bridge area, the 17th Street Canal levee, and the London Avenue 
Canal on the east bank of the canals flood wall and levee. Additional details 
on the levees may be found in the USACE Interagency Performance Evaluation Task 
Force Interim Status Report 1, Performance Evaluation of the New Orleans and 
Southeast Louisiana Hurricane Protection System, dated 10 January 2006. 

A more detailed discussion of the storm surge and the wind analyses is provided 
in the following sections. 

1.1.2 Storm Surge Analysis and Discussion

The storm surge in Alabama, Louisiana, and Mississippi caused severe flood 
damage to residential, commercial, and public buildings, and infrastructure. The 
surge brought high waves and carried floodborne debris, significantly impacting 
and destroying buildings.

To assist in the long-term recovery and mitigation effort, FEMA performed a 
coastal high water marks (HWMs) study to investigate the high water conditions 
through out the impacted areas. The HWMs were surveyed by FEMA and the U.S. 
Geological Survey (USGS). HWMs were surveyed horizontally on the North American 
Datum of 1983 (NAD 83), Mississippi East State Plane Coordinates, and vertically 
in NAVD 88. The HWM elevations were also converted to the National Geodetic 
Vertical Datum of 1929 (NGVD 29) to aid review of data and maps available only 
in the NGVD 29 datum. The HWMs were classified as one of three basic types: 
surge only, surge and waves, or wave runup.

[Begin text box]
HWM Classification Types
Circle = Coastal  surge only
Triangle = Coastal  surge and waves
Box = Coastal  wave runup
[End text box]

1.1.2.1 Mississippi  High Water Marks

The HWM data collected for this study demonstrate that the Hurricane Katrina 
coastal storm surge and wave-related high water conditions reached historical 
proportions and covered significant portions of the Mississippi study area. A 
total of 402 HWMs were surveyed in the three counties investigated, as shown in 
Figure 1-3. Surge elevations along the open coast generally exceeded 23 feet in 
Hancock and Harrison Counties, and over 17 feet in Jefferson County. The highest 
surge HWMs along the open coast were discovered in Hancock and Harrison Counties 
on each side of the opening to St. Louis Bay. This high surge was evident in the 
communities of Lake Shore, Clermont Harbor, and Bay St. Louis in Hancock County, 
and Pass Christian and Long Beach in Harrison County; the highest surge 
elevation surveyed was 28.1 feet and the highest HWM with waves was 34.9 feet. 
Figure 1-4 illustrates a typical map of the HWMs in Harrison County. Maps of the 
all counties surveyed are provided in Appendix F.

Figure 1-3. Locations of the high water marks in Mississippi 
SOURCE: FEMA

Figure 1-4. Locations of the high water marks in Harrison County, Mississippi
SOURCE: FEMA

1.1.2.2 Louisiana  High Water Marks

A total of 482 HWMs were surveyed in eastern Louisiana, as shown in Figure 1-5. 
The locations, elevations, and descriptions of these HWMs have been tabulated 
into a digital database and are summarized in Appendix F. An overall discussion 
of the HWM elevations for the various study areas are presented in the following 
sections. 

Figure 1-5. Locations of the high water marks in Louisiana
SOURCE: FEMA

1.1.2.3 Coastal Areas 

Overall, the Hurricane Katrina storm surge in south-central Louisiana was lower 
compared to many areas of eastern Louisiana and along the entire Mississippi 
Coast, because the storm made landfall in the eastern part of the state. The 
areas of the greatest impact were those where the highest winds generated in the 
right-front quadrant of the storm, pushing the water toward the coast until the 
topography of the land surface was such that it caused a piling up of the water. 
These areas include St. Bernard Parish on the open Gulf Coast and the parishes 
surrounding Lake Ponchartrain, which include St. Tammany, Tangipahoa, 
Livingston, St. John the Baptist, St. Charles, Jefferson, and Orleans. The Gulf 
of Mexico coast forms a large embayment from Plaquemines Parish, extending north 
then east along the Mississippi Gulf Coast. Figure 1-6 illustrates a typical map 
of HWMs for Plaquemines Parish. As the storm advanced toward the coast and 
eventual landfall, water was pushed into this area by the high winds. HWM 
elevations varied in St. Bernard Parish. Typical HWM elevations ranged from 10 
to 12 feet; however, some were as high as 17 to 19 feet (see Appendix F).

Figure 1-6. Example of map illustrating high water marks surveyed in Plaquemines 
Parish, Louisiana
SOURCE: FEMA

1.1.2.4 Lake Ponchartrain

Moderate surge levels were recorded on the western shore of the lake (see 
Appendix F). Due to the extensive marsh and swamp land in this area, it was 
difficult to collect HWMs. Surge elevations in this area ranged from 2.8 feet 
inland west of Lake Maurepas in Livingston Parish to 6.4 feet in St. Charles 
Parish (see Appendix F).

As the storm approached New Orleans, strong winds blowing from the east forced 
water into Lake Ponchartrain from the Gulf of Mexico, causing the elevation of 
the lake to rise. This increased volume of water was pushed by these winds and 
piled up onto the northern shore of the lake, resulting in storm surge extending 
north as far as U.S. Highway 190 in Slidell, to Interstate 12 north of 
Mandeville (see Appendix F). As the eye of the storm followed its northeast 
track, the wind direction shifted and began blowing to the south. This resulted 
in the lake water being pushed southward, allowing it to pile up on the southern 
shoreline.

On the northern shore of the lake, HWMs recorded surge levels ranging from 7 to 
16 feet, with the general trend of the highest values on the east end of the 
north shore working westward to the lower surge values. Coastal storm surge 
elevations of 12.5 to 13.5 feet were recorded in the Slidell vicinity (see 
Appendix F). The same general pattern of higher elevations, topping at 16.6 
feet, on the eastern end of Lake Ponchartrain trending to lower elevations, down 
to 6.8 feet, on the western end, was recorded on the southern shore of the lake 
(see Appendix F). These HWMs are all found on the lake side of the levee system. 

1.1.2.5 Southern Area

The coastal areas least affected by Hurricane Katrina were those parishes 
located in the left and trailing quadrants of the storm. These include 
Terrebonne, Lafourche, and southern Jefferson Parishes. These parishes are 
sparsely populated with few roads giving access. As illustrated in Appendix F, 
these areas are also extensively covered by marshland and swamp. This terrain 
significantly lessens the impact caused by storm surge, as it applies a 
dampening effect to the water as it moves inland. Unfortunately, this type of 
terrain also lessens the availability of HWMs to be located and flagged. 
Appendix F shows the locations and elevations of the HWMs surveyed in these 
parishes. Only one HWM was found and flagged in Terrebonne Parish; seven were 
flagged and surveyed in Lafourche Parish. As Hurricane Katrina tracked farther 
inland on its northeastern path, the water in Barataria Bay was pushed southward 
over Grand Isle. HWM elevations were the highest in this portion of the state, 
measuring between 5.8 and 8.9 feet (see Appendix F).

1.1.2.6 Alabama  High Water Marks

In Alabama, a total 222 HWMs were surveyed in Baldwin and Mobile Counties, as 
shown in Figure 1-7. The locations and elevations of the HWMs are summarized in 
Appendix F.

Figure 1-7. Locations of the high water marks in Alabama
SOURCE: FEMA

The Hurricane Katrina storm surge in Alabama was relatively high. The storm made 
landfall near the Louisiana and Mississippi state line, 65 miles west of the 
Alabama/Mississippi boundary. However, Katrina had a wind field that was skewed 
to the east and this resulted in hurricane force winds extending about 120 miles 
from the storm center. This caused a considerable storm surge at several places 
along the Alabama coast. HWMs varied throughout the two counties, typically from 
10 to 12 feet on the northern end of Mobile Bay (see Figure 1-8), 8 to 10 feet 
along the central shorelines of Mobile Bay, and 9 to 11 feet on Dauphin Island, 
Alabama. Maps of HWMs in other areas of Alabama are shown in Appendix F.

Figure 1-8. High water mark locations for area covering the northern end of 
Mobile Bay
SOURCE: FEMA

1.1.2.7 Factors Affecting Storm Surge

As illustrated with the HWM data discussed in the preceding subsections, the 
peak storm surge in Hurricane Katrina exceeded the prior U.S. record set by 
Hurricane Camille, which hit in the same region of the Mississippi Coast. The 
fact that both records were set in the same geographic area is not just a result 
of two severe hurricanes striking coastal Mississippi; storm surges there are 
amplified by physical features, and a hurricane of a given intensity will cause 
higher storm surges in coastal Mississippi than almost anywhere else along the 
entire coast of the United States.
 
The two primary factors that amplify Mississippis storm surge are the shallow 
offshore depths and the shape of the shoreline. As a storm surge advances toward 
the shoreline, it tries to return via the bottom of the water column. Along 
coasts with steep offshore slopes (e.g., the southeast coast of Florida, or the 
Pacific Coast), return flow effectively moderates the rise in water elevation. 
However, the shallow depths offshore of Mississippi restrict the return flow and 
lead to higher surge elevations over land. The shoreline shape also determines 
whether and how the storm surge can escape as the hurricane approaches. On a 
straight shoreline, the surge can partially escape at each end of the shoreline, 
reducing the peak elevations. The Mississippi River Delta along the Louisiana 
and Mississippi shoreline forms a bay-like feature that effectively confines the 
surge and amplifies the elevation as a hurricane moves ashore.

These surge effects are best isolated by comparing results of the Sea, Lake, and 
Overland Surges from Hurricanes (SLOSH) storm surge model prepared by NOAA. 
Using an array of storm tracks on local bathymetric grids, a worst-case storm 
surge is produced for Category 1 through 5 hurricanes. A comparison of three 
categories of storms along the Gulf Coast is shown in Figure 1-9.

Figure 1-9. Maximum SLOSH storm surge predictions for open coast, developed 
shorelines
SOURCE: SLOSH Display CD-ROM/January 5, 2006/NOAA  
Mississippi Coast SLOSH (NOAA) Data

Only the developed areas along the open coast areas are included in Figure 1-9, 
to exclude storm surge amplification in the more inland bays. Predicted worst-
case storm surge elevations (without waves) are shown along the Gulf Coast from 
Galveston, Texas, to south of Tampa Bay, Florida. The figure shows that, for a 
given category storm, most areas of the Gulf Coast (i.e., Texas, Western 
Louisiana, Alabama, the Florida panhandle, and the lower Florida Peninsula) will 
experience similar storm surges, with the exception of two areas  the 
Mississippi Coast and the Big Bend area of Florida, where the surge elevations 
are roughly 50 to 100 percent higher than those experienced along most of the 
Gulf Coast. The bay effect of the Mississippi Delta can be seen as the increase 
from Pilot Town on the outer end of the delta to a flat peak from Pass Christian 
to Biloxi, dropping in Eastern Mississippi. 

In addition to unusually high storm surge potential for any given storm, 
Mississippi has one of the highest chances of a landfalling hurricane  and, in 
some sections, the highest design wind speeds in the country. Therefore, it is 
not a random coincidence that Hurricanes Katrina and Camille set storm surge 
records in Mississippi. 

Figure 1-10 shows the NOAA SLOSH model estimating the maximum storm surge along 
the Gulf Coast as a result of Hurricane Katrina. The storm surge in the 
Gulfport-Biloxi area was estimated to exceed 23 feet. 

Figure 1-10. The SLOSH model of high water elevations for Hurricane Katrina 
SOURCE: NOAA

Figure 1-11 shows the primary factors driving Katrinas storm surge as the eye 
of the hurricane reached the Louisiana Delta (a) and the Mississippi shoreline 
(b). Although the initial landfall of the eye was across Plaquemines Parish, 
Louisiana, the radius of maximum winds remained principally east of the delta 
and made landfall in Mississippi. The counter-clockwise winds around the eye 
forced water into the shallow, western corner of Mississippi Bay, with escape 
prevented by the long branches of the Louisiana Delta.

[Begin Figure]
Figure 1-11. H*Wind [footnote 6] snapshots of Katrina 1-minute winds as the eye 
reached the Louisiana Delta (a) and Mississippi shoreline (b). Counter-clockwise 
winds pushed peak storm surge into the west end of the Mississippi Bay.
SOURCE: NOAA, Atlantic Oceanographic and Meteorological Laboratory [AOML], 
Hurricane Research Division [HRD]

a) Louisiana Delta 
Hurricane Katrina 1200 UTC 29 AUG 2005
Max 1-min sustained surface winds (kts)
Observed Max. Surface Winds: 101 kts, 40 nm SE of center based on 1159zSFMR43 
sfc measurement
Analyzed Max. Wind: 101 kts, 40 nm NE of center

b) Mississippi Shoreline
Hurricane Katrina 1500 UTC 29 AUG 2005
Max 1-min sustained surface winds (kts)
Observed Max. Surface Winds: 101 kts, 41 nm SE of center based on 1159zSFMR43 
sfc measurement
Analyzed Max. Wind: 101 kts, 36 nm SE of center

Footnote 6. One of the better known products for representing hurricane winds is 
H*Wind from NOAA's Hurricane Research Division. H*Wind is an experimental 
research product developed by the HRD.
[End Figure]

Several other factors contributed to Katrina's record storm surge. The storm was 
very large, with hurricane wind speeds covering approximately 200 miles in 
diameter as it came ashore. As described previously, Katrinas wind speeds and 
central pressure were that of a very strong Category 5 hurricane within a 
hundred miles of the coast. The surface flow and deepwater wave heights were 
therefore initiated under these higher wind speeds. If the offshore conditions 
of the storms strength had been similar to those at landfall, storm surge 
elevations would have been lower. 
In short, it is not surprising that Katrina caused high storm surges along the 
western Mississippi coastline. The shallow offshore slope and the confining 
corner created by the Louisiana Delta make it predictable that a hurricane of 
any intensity on a similar track would result in a higher storm surge than along 
most other shorelines in the United States. Refer to Section 1.1.3 for more 
information on H*Wind.

1.1.2.8 Coastal Flood Frequency Analysis

Under a separate Hazard Mitigation Technical Assistance Program (HMTAP) Task 
Order, URS was tasked to prepare Flood Advisory Maps for the three counties in 
Mississippi that were affected by Hurricane Katrina. Part of this task involved 
performing a flood frequency analysis of tidal gauge data to quickly provide 
information to assist in the planning and rebuilding efforts, while more 
detailed analyses are being conducted. The results of this study are provided in 
Draft Report, Hurricane Katrina Flood Frequency Analysis, dated September 2005. 
The analysis was based on 30 years' worth of tidal gauge data collected from 
NOAA and USGS. 

The long-term gauge analysis was based on Hurricane Katrina gauge data from 
select NOAA and USACE stations. While the best data available were used at the 
time of the flood frequency analysis, the reference data had limitations. Some 
stations were damaged, destroyed, or malfunctioned during Hurricane Katrina and 
did not record the peak stage. Another limitation was that gauges with long 
records of data were sparsely distributed, but they did provide useful records 
of a long period of historic storm surge peak heights. Preliminary HWM surveys 
in the vicinity of the existing gauge were used in the analysis.

The historical data were analyzed using seven different methods to estimate the 
2-, 10-, 50-, 100-, and 500-year elevations. Methods of the analysis include the 
Weibull and Cunnane plotting positions, the Pearson Type III and log-Pearson 
Type III distribution, the Generalized Extreme Value (GEV) distribution, and the 
Gumbel distribution using both untransformed and log-transformed elevation data. 
Details on the analysis, including the gauge data and the frequency 
distributions, may be found in the report. 

The following is a summary of the results from the Hurricane Katrina Flood 
Frequency Analysis report:

- At Biloxi, the 100-year elevation is 15.7 feet and the 500-year elevation is 
28.7 feet. Therefore, the Hurricane Katrina elevation of 24 feet is estimated to 
be about a 250-year event at Biloxi, Mississippi.

- At Pascagoula, the 100-year elevation is 11.9 feet and Katrina was 13 feet. 
Katrina is estimated to be about a 125-year event at Pascagoula, Mississippi.

- At Waveland, the 100-year elevation is 17.6 feet and Katrina was 23 feet. The 
200-year event is 22.8 feet; therefore, Katrina is estimated to be about a 200-
year event at Waveland. Note that the Katrina elevation of 23 feet was estimated 
from four HWMs obtained by USGS at a location north of Waveland near the 
intersection of I-10 and SR 43. It is possible that Katrina was higher than 23 
feet at Waveland. The elevations of HWMs flagged at Waveland had not yet been 
determined when the Flood Frequency Analysis report was written.

- On the west end, bay side of Dauphin Island, the 100-year event is 7.5 feet 
and Katrina was 5.81 feet. The 50-year event is 6 feet; Katrina was about a 50-
year event on the west end, bay side of Dauphin Island, Alabama.

- At Pensacola, the 100-year event is 7.3 feet and Katrina was 6.07 feet. The 
50-year event is in the range of 5.8 feet, so Katrina is estimated to be about a 
50-year event at Pensacola, Florida.
The results of the flood frequency analysis were used to develop Advisory Base 
Flood Elevations (ABFEs) and prepare the Katrina Recovery Maps.

1.1.2.9 Flood Recovery Maps

FEMA requested that URS evaluate coastal flood hazard conditions for Hurricane 
Katrina in Mississippi using data from the Flood Frequency Analysis and the High 
Water Mark Study, and prepare surge inundation and ABFE maps. The Hurricane 
Katrina Surge Inundation and ABFE maps (herein referred to as the "Katrina 
Recovery Maps") were provided in the form of high resolution maps that show 
coastal flood impacts for Mississippi and Louisiana. 

These maps can be viewed at 
<http://www.fema.gov/hazard/flood/recoverydata/katrina/>. A sample of a Katrina 
Recovery Map is shown in Figure 1-12.

Figure 1-12. Sample recovery map, which illustrates surge inundation and ABFEs 
for Hancock County, Mississippi
SOURCE: FEMA

1.1.3 Wind Hazard Analysis and Discussion

According to the National Weather Service (NWS) December 20, 2005, report, 
Hurricane Katrina made landfall in Buras, Louisiana, with an estimated 1-minute 
sustained wind speed of 110 knots (127 mph) or approximately 150 mph 3-second 
gust. After landfall in Louisiana, Katrina traveled almost 100 miles across the 
Louisiana Delta before reaching the Mississippi coast where it made a third 
landfall (one in Florida and two in the Gulf) near Poplarville, Mississippi. The 
NWS estimated 1-minute sustained surface winds of 105 knots (120 mph) or 
approximately 145 mph 3-second gust.

The estimates were higher than any recorded by land-based instruments. The 
highest land-based wind speed recorded was 117 mph gust from a Texas Tech 
University tower located at the Stennis International Airport, approximately 8 
miles west-northwest of Bay St. Louis, Mississippi. However, like many previous 
storms the MAT has investigated, ground-based anemometers either failed before 
they recorded maximum winds or were located great distances from the storms 
path. As a result, no wind speed instruments likely recorded the maximum winds 
produced by Katrina.

Table 1-3 provides a summary of some of the data available from the measuring 
devices, including recorded wind speed, location, and the source of the data. 
Wind speeds have been converted from knots to mph. 

[Begin Table]
Table 1-3. Wind Speeds Recorded for Hurricane Katrina

Location: Alabama: Dauphin Island at Coastal Marine Automated Network (C-MAN) 
Station DPIA1 (Source: NWS)
Wind Speed: 101 mph gust
 
Location: Louisiana: Slidell (Source: Texas Tech University mobile wind tower)
Wind Speed: 100 mph gust
 
Location: Louisiana: BelleChasse (Source: FCMP mobile wind tower T1)
Wind Speed: 102 mph gust
 
Location: Louisiana: Galliano (Source: FCMP mobile wind tower T2)
Wind Speed: 96 mph gust
 
Location: Louisiana: Vacherie (Source: Texas Tech University)
Wind Speed: 73 mph gust (data collection ceased near the storms peak)
 
Location: Louisiana: Grand Isle (Source: NOAA Buoy GDIL1)
Wind Speed: 114 mph gust, before gauge failed
 
Location: Louisiana: Port Sulfur (Source: LSU AgCenter)
Wind Speed: 101 mph gust, peak before station failed
 
Location: Louisiana: Buras (Source: University of Louisiana near Buras 
reporting)
Wind Speed: 114 mph gust (2 meter tower on top of a levee)
 
Location: Mississippi: Stennis International Airport (Source: Texas Tech 
University)
Wind Speed: 117 mph gust
 
Location: Mississippi: Biloxi (Source: ASOS)
Wind Speed: 111 mph gust (max gust before failing) 
 
Location: Mississippi: Pine Belt Airport (12 miles NE of Hattiesburg) 
Wind Speed: Max gust 80 mph. After this, power was lost and recording stopped.
 
Location: Mississippi: Forrest County Emergency Operations Center (EOC) 
Wind Speed: Max gust 100 mph. After this, the anemometer was blown down.
 
Location: Mississippi: Laurel-Jones County Airport 
Wind Speed: Max gust of 110 mph. After this, the anemometer was blown down.
 
Jackson International Airport
Wind Speed: Max gust of 64 mph (10 seconds), unofficial gust of 74 mph (5 
seconds). After this, power was lost and recording stopped.

Pascagoula (Source: FCMP mobile wind tower T3)
Wind Speed: 95 mph gust

SOURCE: NOAA, NCDC
The wind speed data listed in this table have not been normalized to a single 
exposure category and instrument height. 
[End Table]

To help fill in the gaps that exist in ground-based wind data, wind speeds are 
estimated using a variety of methods.

H*Wind employs estimates of surface level winds obtained from a variety of 
sources and yields near real-time analyses of the surface winds produced by 
tropical cyclones. Based on past experience of comparing modeled estimates with 
actual recorded wind speeds, H*Wind provides reasonably accurate estimates of 
maximum wind speeds over large areas impacted by a storm. Contours of 1-minute 
sustained wind speeds from Katrina were developed utilizing HRD's H*Wind model 
(see Figure 1-11). The contours are at selected "snapshots" taken as Katrina's 
eye passed over Plaquemines Parish and over Breton Sound.

FEMAs wind model used in HAZUS-MH (Hazards U.S. - Multi-Hazard) is also used to 
estimate wind speeds. HAZUS was developed as a loss estimation model, but 
produces reasonable estimates of maximum speed and the lateral distribution of 
wind. Wind swath contour plots based on HAZUS-MH methodology were modeled by 
Applied Research Associates (ARA) (see Figure 1-13). ARAs model uses a series 
of surface level observations of wind speeds and pressures obtained from 
portable towers, buoys, and Automated Surface Observing Systems (ASOS) stations 
to obtain estimates of the time variation in the storm's radius to maximum winds 
and the Holland B parameter (a function of the shape of the storm). Measured 
wind speeds are adjusted to standard conditions (that is 10 meter instrument 
height in open terrain) using either estimates of the surrounding roughness from 
aerial photography or from estimates of the turbulence intensity where full 
digital time series are available. The variation of the Holland parameter B is 
used with NHC position and central pressure estimates and pre-computed solutions 
of a numerical hurricane model to develop estimates of wind speeds as a function 
of time and location. Unlike the H*Wind snapshots shown in Figure 1-11, Figure 
1-13 shows the highest estimated wind speeds experienced as Katrina moved 
through the area.

Figure 1-13. Wind swath contour plot of 3-second gust wind speeds in mph at a 
height of 10 meters above ground (open exposure) based on HAZUS-MH wind field 
methodology
SOURCE: ARA 

In the case of Hurricane Katrina, there were very little wind speed and pressure 
data inland and, as a result, estimates of wind speeds farther inland have 
greater uncertainty than those near the coast. Comparisons to anemometer data 
suggest the model has an uncertainty (estimated using the standard deviation of 
the observed minus modeled wind speeds) of about 6 percent, indicating that, in 
most cases, the modeled wind should be accurate to about 10 percent or better. 

With Katrina, wind speeds generated by the HAZUS model and those estimated 
utilizing the H*Wind results compare favorably to each other. Also, both methods 
suggest that, except for a few areas along the Mississippi coast, Katrina's 
winds failed to reach the design wind speeds specified by ASCE 7 (the wind 
standard referenced by the latest building codes).

The modeled wind speeds also generally correlate with damages observed by the 
MAT, particularly when the model results are adjusted for exposure (HAZUS and 
H*Wind depict wind speeds in Exposure C (open terrain) areas; most of the MAT 
observations were in the more protected Exposure B areas). Exceptions to this 
general correlation occurred in some areas east of Gulfport and north of 
Picayune. In those areas, HAZUS predicted higher wind speeds than what the 
observed ground-based damages would appear to support. For example, HAZUS 
predicted wind speeds in Biloxi only 5 mph less than Bay St. Louis, but the 
observed wind damages in Biloxi were significantly less than those in Bay St. 
Louis. Also, HAZUS predicted 115 mph Exposure C wind speeds in Poplarville, but 
the damages observed in that area were more typical of lower wind speeds. The 
apparent lack of correlation between ground-based damage observations and the 
computer models in these areas may result from terrain effects, from 
construction variations, or from the uncertainty of the computer models. 

[Begin text box]
DEFINITION OF WIND EXPOSURE ZONES 
Exposure B. Urban, suburban, wooded areas.
Exposure C. Open terrain, flat open country, grasslands, all water surfaces in 
hurricane-prone regions.
[End text box]

Much of the wind-based damage from Hurricane Katrina occurred in areas where the 
wind speeds were well below the design levels specified in the latest codes. In 
discussing wind damage, it is important to differentiate between structural 
damage and building envelope damage. Many buildings experienced little or no 
structural damage, but may be total losses due to water entry that resulted from 
building envelope failure. It is also important to differentiate between the 
design wind speeds and their resulting design pressures specified by the latest 
codes and the design wind speeds/pressures specified by the older codes that 
were in effect when many of the buildings the MAT investigated were constructed. 
In many areas, the design wind pressures specified in current codes are higher 
than those specified in older codes.

Table 1-4 lists the HAZUS-modeled Exposure C wind speeds in selected cities and 
converted wind speeds for Exposure B areas. The conversion from Exposure C to 
Exposure B was made using an equivalent wind pressure calculation using 
equations contained in ASCE 7-05. 

[Begin Table]
Table 1-4. HAZUS Estimated Wind Speeds

Location: Bay St. Louis, MS
3 Second Gust Wind Speeds* Exposure C: 125
3 Second Gust Wind Speeds** Exposure B: 105
 
Location: Belle Chasse, LA
3Second Gust Wind Speeds* Exposure C: 110
3Second Gust Wind Speeds** Exposure B: 95 
Biloxi, MS
3Second Gust Wind Speeds* Exposure C: 120
3Second Gust Wind Speeds** Exposure B: 100
 
Location: DIberville, MS
3Second Gust Wind Speeds* Exposure C: 120
3Second Gust Wind Speeds** Exposure B: 100
 
Location: Dauphin Island, AL
3Second Gust Wind Speeds* Exposure C: 95
3Second Gust Wind Speeds** Exposure B: 80
 
Location: Diamondhead, M
3Second Gust Wind Speeds* Exposure C:  120
3Second Gust Wind Speeds** Exposure B: 100
 
Location: Gautier, MS
3Second Gust Wind Speeds* Exposure C: 110
3Second Gust Wind Speeds** Exposure B: 95
 
Location: Gulfport, MS
3Second Gust Wind Speeds* Exposure C: 130
3Second Gust Wind Speeds** Exposure B: 110
 
Location: Long Beach, MS
3Second Gust Wind Speeds* Exposure C: 130
3Second Gust Wind Speeds** Exposure B: 110
 
Location: Mobile, AL
3Second Gust Wind Speeds* Exposure C: 85
3Second Gust Wind Speeds** Exposure B: 70
 
Location: Moss Point, MS
3Second Gust Wind Speeds* Exposure C: 100
3Second Gust Wind Speeds** Exposure B: 85
 
Location: New Orleans, LA
 3Second Gust Wind Speeds* Exposure C: 105
3Second Gust Wind Speeds** Exposure B: 90
 
Location: Ocean Springs, MS
3Second Gust Wind Speeds* Exposure C: 120
3Second Gust Wind Speeds** Exposure B: 100
 
Location: Pascagoula, MS
3Second Gust Wind Speeds* Exposure C: 105
3Second Gust Wind Speeds** Exposure B: 90
 
Location: Pass Christian, MS
3Second Gust Wind Speeds* Exposure C: 130
3Second Gust Wind Speeds** Exposure B: 110
 
Location: Poplarville, MS
3Second Gust Wind Speeds* Exposure C: 115
3Second Gust Wind Speeds** Exposure B: 100
 
Location: Slidell, LA
3Second Gust Wind Speeds* Exposure C: 115
3Second Gust Wind Speeds** Exposure B: 100
 
Location: Waveland, MS
3Second Gust Wind Speeds* Exposure C: 125
3Second Gust Wind Speeds** Exposure B: 105

 * Wind speeds based on ARA wind speeds as shown in Figure 1-13.
** Calculated wind speeds, Exposure B  calculated from wind pressure 
conversions for components and cladding for buildings with a mean roof height of 
33 feet (see ASCE 7-05 Table 6-3). 
[End Table]

[Begin text box
Tornadoes from Hurricane Katrina
According to the NCDC, there were 13 confirmed tornadoes in Mississippi, ranging 
from F1 to F2, and 11 confirmed tornadoes in Alabama, ranging from F0 to F1, as 
a result of Hurricane Katrina occurring on August 28 and 29, 2005. At the time 
the report was being developed, data for Louisiana were not available. 
Locations of the confirmed tornadoes are shown in Figure 1-14. Most of the 
tornadoes were rated F0 or F1 on the Fujita Scale, as shown in Table 1-5. 
[End text box]

[Begin Table]
Table 1-5. The Fujita Scale

F-Scale Number: F0
Intensity Phrase: Gale tornado
Wind Speed: 40-72 mph
Type of Damage Done: Some damage to chimneys; breaks branches off trees; pushes 
over shallow-rooted trees; damages sign boards.
 
F-Scale Number: F1
Intensity Phrase: Moderate tornado
Wind Speed: 73-112 mph
Type of Damage Done: The lower limit is the beginning of hurricane wind speed; 
peels surface off roofs; mobile homes pushed off foundations or overturned; 
moving autos pushed off the roads; attached garages may be destroyed.
 
F-Scale Number: F2
Intensity Phrase: Significant tornado
Wind Speed: 113-157 mph
Type of Damage Done: Considerable damage. Roofs torn off frame houses; mobile 
homes demolished; boxcars pushed over; large trees snapped or uprooted; light 
object missiles generated.
 
F-Scale Number: F3
Intensity Phrase: Severe tornado
Wind Speed: 158-206 mph
Type of Damage Done: Roof and some walls torn off well constructed houses; 
trains overturned; most trees in forest uprooted.
 
F-Scale Number: F4
Intensity Phrase: Devastating tornado
Wind Speed: 207-260 mph
Type of Damage Done: Well-constructed houses leveled; structures with weak 
foundations blown off some distance; cars thrown and large missiles generated.
 
F-Scale Number: F5
Intensity Phrase: Incredible tornado
Wind Speed: 261-318 mph
Type of Damage Done: Strong frame houses lifted off foundations and carried 
considerable distances to disintegrate; automobile sized missiles fly through 
the air in excess of 100 meters; trees debarked; steel reinforced concrete 
structures badly damaged.
 
F-Scale Number: F6
Intensity Phrase: Inconceivable tornado
Wind Speed: 319-379 mph
Type of Damage Done: These winds are very unlikely. The small area of damage 
they might produce would probably not be recognizable along with the mess 
produced by F4 and F5 winds that would surround the F6 winds. Missiles, such as 
cars and refrigerators, would do serious secondary damage that could not be 
directly identified as F6 damage. If this level is ever achieved, evidence for 
it might only be found in some manner of ground swirl pattern, for it may never 
be identifiable through engineering studies.
[End Table]

Figure 1-14. Confirmed tornadoes in Mississippi and Alabama attributed to 
Hurricane Katrina 
(BASED ON NATIONAL CLIMATIC DATA CENTER RECORDS)

1.2 Historic Hurricanes

At its peak in the Gulf, Hurricane Katrina reached a minimum central pressure of 
902 mb, although at landfall it weakened to 920 mb. Other severe hurricanes (and 
the minimum central pressure at landfall) were Hurricane Camille (909 mb) and 
the Labor Day hurricane that struck the Florida Keys in 1935 (892 mb). Hurricane 
Andrew in 1992 recorded a pressure of 922 mb at landfall and destroyed over 
25,000 houses and damaged over 100,000 houses. Hurricanes Rita and Wilma, which 
occurred in 2005, recorded some of the lowest pressures in history. Table 1-6 
provides a summary of the most intense hurricanes to make landfall on the U.S. 
mainland. 

[Begin Table]
Table 1-6. Summary of Most Intense Hurricanes to Make Landfall in the United 
States Based on Minimum Pressure

Hurricane: Wilma
Minimum Pressure (millibars): 882
Pressure at Landfall (millibars): 950
Category at Landfall: 3
Location: near Everglades City, FL
Year: 2005
 
Hurricane: Unnamed Storm
Minimum Pressure (millibars): 892
Pressure at Landfall (millibars): 892 
Category at Landfall: 5
Location: Florida Keys
Year: 1935
 
Hurricane: Rita
Minimum Pressure (millibars): 897
Pressure at Landfall (millibars): 937
Category at Landfall: 3
Location: Texas/Louisiana border
Year: 2005
 
Hurricane: Allen
Minimum Pressure (millibars): 899
Pressure at Landfall (millibars): 948
Category at Landfall: 3
Location: south Texas
Year: 1980
 
Hurricane: Katrina
Minimum Pressure (millibars): 902
Pressure at Landfall (millibars): 920
Category at Landfall: 3
Location: Plaquemines Parish, near Buras, LA
Year: 2005
 
Hurricane: Camille
Minimum Pressure (millibars): 905
Pressure at Landfall (millibars): 909
Category at Landfall: 5
Location: Mississippi
Year: 1969
 
Hurricane: Andrew 
Minimum Pressure (millibars): 922
Pressure at Landfall (millibars): 922
Category at Landfall: 5
Location: southeast FL - Homestead, FL
Year: 1992

SOURCE: NOAA, NCDC, Climate of 2005 Atlantic Hurricane Season
[End Table]
When discussing past hurricanes, many residents of southeast Louisiana and the 
Gulf Coast of Mississippi had always referred to the power, high surge 
elevations, wind speeds, and resultant damage of Hurricanes Betsy and Camille 
for comparison. Now the benchmark for future hurricanes has become Hurricane 
Katrina. In Alabama, Dauphin Island residents referred to the destruction caused 
by Hurricane Frederic. Table 1-7 shows the comparisons for Hurricanes Betsy, 
Camille, Frederic, and Katrina. Figure 1-15 shows the paths of Hurricanes Betsy, 
Camille, Frederic, and Katrina. 

[Begin Table]
Table 1-7. Comparisons of Hurricanes Betsy, Camille, Frederic, and Katrina

Hurricane: Betsy
Year: 1965
Category at Landfall: 3
Surge Elevation (feet): 16
Wind Speed-gust (mph) at Landfall: 160
Central Pressure (mb) at Landfall: 948
Casualties: 76
Economic Loss (billions) (adjusted 2005): $10-12
Number of Homes Damaged/Destroyed: 164,000
 
Hurricane: Camille
Year: 1969
Category at Landfall: 5
Surge Elevation (feet): 25
Wind Speed-gust (mph) at Landfall: 190
Central Pressure (mb) at Landfall: 909
Casualties: 256
Economic Loss (billions) (adjusted 2005): $6.99
Number of Homes Damaged/Destroyed: 19,577
 
Hurricane: Frederic
Year: 1979
Category at Landfall: 3
Surge Elevation (feet): 12
Wind Speed-gust (mph) at Landfall: 145
Central Pressure (mb) at Landfall: 946
Casualties: 5
Economic Loss (billions) (adjusted 2005) $7.3
Number of Homes Damaged/Destroyed: N/A
 
Hurricane: Katrina
Year: 2005
Category at Landfall: 3
Surge Elevation (feet): 28
Wind Speed-gust (mph) at Landfall: 150
Central Pressure (mb) at Landfall: 920
Casualties: >1,700
Economic Loss (billions) (adjusted 2005): $125
Number of Homes Damaged/Destroyed: >300,000
 
SOURCE: NOAA, NCDC
[End Table]

Figure 1-15. Historic hurricane storm tracks: Betsy (1965), Camille (1969), 
Frederic (1979), and Katrina (2005)
(BASED ON HURRICANE STORM TRACK DATA FROM THE NATIONAL HURRICANE CENTER)

1.2.1 Hurricane Betsy

A major hurricane of the 1965 hurricane season, Hurricane Betsy tracked through 
the Bahamas and Florida before reaching Louisiana, causing major damage along 
its path. Betsy made landfall on September 9, 1965, as a Category 3 Hurricane at 
Grand Isle, Louisiana, bringing 160-mph gusts and a 16-foot storm surge that 
flooded the entire island. Winds gusted to 125 mph in New Orleans and a 10-foot 
storm surge caused major flooding. Winds in most of southeast Louisiana reached 
100 mph and, in areas as far inland as Monroe, winds exceeded 60 mph. Offshore 
oil rigs, public utilities, and commercial boats all suffered severe damage, 
resulting in approximately $1.4 billion in damage (in 1965 dollars, the 
equivalent of approximately $10-12 billion in 2005). Seventy-six people lost 
their lives as a direct result of Hurricane Betsy, the first storm to cause $1 
billion in damage. Figure 1-16 shows all hurricane storm tracks in the Gulf 
Coast catchers mitt from 1851 to the present, according to the NHC.

Figure 1-16. Historic hurricane storm tracks and categories (1851  present) 
(BASED ON HURRICANE STORM TRACK DATA FROM THE NATIONAL HURRICANE CENTER) 

Like Katrina, Betsy caused surge effects in Lake Pontchartrain. The storm surge 
from the lake caused a section of the levee to fail, resulting in flooding 
within New Orleans in the Ninth Ward and in the Chalmette area of St. Bernard 
Parish. In most low-lying areas of the city, floodwaters reached to the roofs of 
houses, resulting in drowning deaths of some of those whom had sought refuge 
from the floodwaters in their attics. Water levels receded after approximately 
10 days. It is estimated that approximately 164,000 homes were flooded in 
Louisiana as a result of Hurricane Betsy.

After Betsy, the USACE created the Hurricane Protection Program and constructed 
a new levee system both higher and stronger than the former system. This system 
protected New Orleans from Hurricane Camilles storm surge in 1969.

1.2.2 Hurricane Camille

Hurricane Camille (1969), the previous hurricane of record for the Mississippi 
Gulf Coast, recorded a 25-foot storm surge. At its peak strength over the Gulf 
(902 mb and 175 mph sustained winds), Katrinas intensity was comparable to 
Camille's, but at landfall Katrinas measured winds (127 mph sustained) were 
lower and its central pressure (920 mb) was higher than Camilles estimated 
landfall measurements of 190-210 mph gust speeds and 909 mb central pressure. 
[Footnote 7] However, Katrina was a larger storm affecting a wider area than 
Camille, and was pushing higher storm surges onshore along the Gulf Coast.

Footnote 7. Camille's landfall measurements are estimates because a 
reconnaissance aircraft was unable to estimate surface wind just prior to the 
storm's landfall and because terrestrial weather observation equipment did not 
survive the storm.

Camille made landfall as a Category 5 hurricane in western coastal Mississippi 
in the Waveland/Bay St. Louis area on August 17, 1969, approximately 15-20 miles 
east of where Katrina made its third landfall near Pearlington, Mississippi. 
Like Katrina, Hurricane Camille brought severe destruction to the Mississippi 
Gulf Coast, causing $1.42 billion in total damage (in 1969 dollars  the 
equivalent of $6.99 billion when adjusted to 2005 dollars), and was directly 
responsible for 143 deaths in Alabama, Louisiana, and Mississippi. Many of those 
who died were residents along the coast who did not evacuate. After losing 
hurricane strength, Camille traveled north, causing major flooding in Virginia 
and leading to the deaths of an additional 113 people. Throughout its path, 
Camille caused injury to 8,931 people, destroyed 5,662 homes, and severely 
damaged 13,915 homes. 

For the past 36 years, Camille has stood out as the benchmark storm for those 
living along the Mississippi Gulf Coast, both in their minds and in records set. 
However, with Hurricane Katrinas arrival in 2005, residents of the area have a 
new standard for devastation and destruction. Although not as powerful as 
Hurricane Camille according to wind speed and pressure measurements at landfall, 
Hurricane Katrina was a much larger diameter storm. The most overwhelming source 
of damage was Katrinas record-breaking storm surge along the Mississippi coast, 
which topped Camilles surge elevations by several feet in most areas. Although 
Hurricane Katrina is considered the new standard for comparing hurricanes along 
the Louisiana and Mississippi Gulf Coast, future storms could equal or exceed 
the impact caused by Katrina.

1.2.3 Hurricane Frederic

In 1979, Hurricane Frederic caused considerable damage along Dauphin Island and 
Gulf Shores, Alabama. Making landfall near Gulf Shores-Mobile, Alabama, peak 
storm surge levels reached 12 feet in Gulf Shores, destroying much of the 
community, and 11 feet at Dauphin Island, destroying the causeway connecting the 
island to the mainland. Over 50 homes were destroyed along the 22-mile reach 
from Fort Morgan to Gulf Shores, and 73 percent of the beachfront buildings were 
destroyed. In comparison, the high surge of Hurricane Katrina was similar to 
that of Hurricane Frederic, in some areas along Dauphin Island. Hurricane 
Katrinas high surge provided a good opportunity to assess the adequacy of 
National Flood Insurance Program (NFIP) floodplain management requirements as 
well as current construction practices in resisting storm surge damage. 

1.3 FEMA Mitigation Assessment Teams (MATs)

Most people know FEMA for its response to disasters and its assistance to people 
impacted by disasters. Another important contribution of the agency is the 
building performance studies it conducts after disasters in order to better 
understand how natural and manmade events affect the built environment. These 
studies are conducted with the intent of reducing the number of lives lost to 
these events and minimizing the economic impact on the communities where these 
events occur. In addition, lessons learned are applied to the rebuilding effort 
after disasters to enhance the disaster-resistance of new building stock. 

Since the mid-1980s, FEMA has sent MATs to Presidentially-declared disaster 
areas to evaluate building performance. The MAT studies the adequacy of current 
building codes, other construction requirements, and building practices and 
materials. Based on estimates from preliminary information of the potential type 
and severity of damage in the affected area(s) and the magnitude of the expected 
hazards, FEMA determines the potential need to deploy one or more MATs to 
observe and assess damage to buildings and structures, as caused by wind, rains, 
and flooding associated with the storm. These teams are deployed only when FEMA 
believes the findings and recommendations derived from field observations will 
provide design and construction guidance that will not only improve the disaster 
resistance of the built environment in the impacted state or region, but will 
also be of national significance to all disaster-prone regions. 
1.3.1 Purpose of the MAT

In response to a request for technical support from FEMA Joint Field Offices in 
Montgomery, Alabama; Baton Rouge, Louisiana; and Jackson, Mississippi, FEMAs 
Mitigation Division deployed a MAT to Alabama, Louisiana, and Mississippi on 
September 26, 2005, to evaluate both building performance during Hurricane 
Katrina and the adequacy of current building codes, other construction 
requirements, and building practices and materials. 

The flood levels for Hurricane Katrina far exceeded the current design flood 
event (i.e., 100-year base flood event), as illustrated on the FEMA Flood 
Insurance Rate Maps (FIRMs), along the entire Gulf Coast of Mississippi, and 
caused levee failures in Louisiana. The wind speeds from Katrina were less than 
the design speeds for most areas based on the model codes (International 
Building Code [IBC]/International Residential Code [IRC]) and on the engineering 
standard (ASCE 7) referenced in the building codes. 

In New Orleans, FEMA was particularly interested in the long-term impacts of 
flooding on the structural and non-structural elements of buildings, as well as 
the floodplain management issues surrounding the levee breaches.

Except at a few locations along the Mississippi coast, Hurricane Katrina was 
below a design level wind event. The storm provided an opportunity to examine 
building elements that failed even when they shouldnt have and the team had 
hoped to determine how buildings built to new building codes performed in those 
areas that did experience near-design wind conditions. However, due to a limited 
stock of buildings built to the newer I-codes and the fact that many areas did 
not experience a design wind event, it was difficult to evaluate the 
effectiveness of the newer codes. The team was able to collect information about 
building damage that helps correlate wind speeds to building performance. 

1.3.2 Team Composition

The MAT included FEMA Headquarters and Regional Office engineers and experts 
from the design and construction industry. Team members from FEMAs database of 
national experts included structural engineers, architects, wind engineers, 
civil engineers, coastal scientists, building code experts, and flood 
preservation specialists. In addition, representatives from the USACE, the 
National Institute of Standards and Technology (NIST), Oak Ridge National 
Laboratory (ORNL), the Association of Floodplain Managers (ASFPM), the 
International Code Council (ICC), and wind engineers and scientists from Texas 
Tech University, Louisiana State University (LSU), and University of Mississippi 
also participated. 

In response to the unique situation presented by the flooding in New Orleans, 
FEMA deployed a portion of the MAT resources (hereafter referred to as the New 
Orleans Flood Team) to observe and assess damage to residential buildings and 
critical and essential facilities from the levee breach flooding associated with 
the storm. Therefore, the New Orleans Flood Team also included experts from the 
flood restoration industry. 

1.3.3 Methodology

Aerial reconnaissance was performed by MAT members to assess overall building 
damage in the areas affected by Katrina on September 11 and 12, 2006. As shown 
in Figure 1-17, the aerial observations were conducted from Dauphin Island, 
Alabama, along the Mississippi Gulf Coast, over New Orleans, and inland over 
Slidell and Mandeville, Louisiana, and Hattiesburg, Mississippi. 

Figure 1-17. Flight paths of aerial reconnaissance conducted by the MAT
(BASED ON http://www.nationalatlas.gov AND MAT GPS POINT LOCATIONS) 

Preliminary field investigations to assess building conditions in limited areas 
were conducted between September 17 and 21. Based on the data collected by the 
aerial reconnaissance and the preliminary field investigations, the area of 
focus for the full MAT was more fully defined. The full MAT was deployed on 
September 26 for 2 weeks, conducting extensive ground observations from Dauphin 
Island, Alabama, along the Mississippi Gulf Coast, through the City of New 
Orleans to Venice and Grand Isle, Louisiana, as shown in Figure 1-18.

Figure 1-18. Locations visited by the MAT 
(BASED ON http://www.nationalatlas.gov AND MAT OBSERVATIONS)

 The MAT focused their efforts in Alabama, Mississippi, and St. Tammany Parish, 
Louisiana, from September 26 through October 3, 2005. In Alabama, the team 
worked on the western coastline, including Dauphin Island, collecting building 
damage data. In Mississippi, the team worked in the states three coastal 
counties performing ground inspections from Pascagoula in Jackson County to 
Waveland and Pearlington in Hancock County. Field investigations to assess 
building conditions in Louisiana began on October 4 and concluded on October 8, 
2005. The team conducted ground inspections throughout the New Orleans area, 
including the City of New Orleans and Orleans Parish, as well as the nearby 
communities of Chalmette in St. Bernard Parish and Metairie in Jefferson Parish. 
Additionally, the team visited affected areas in Plaquemines and Lafourche 
Parishes. 

Damages were observed to single- and multi-family buildings, manufactured 
housing, commercial properties, and historic buildings. In addition, critical 
and essential facilities, such as Emergency Operations Centers (EOCs), fire and 
police stations, hospitals, nursing homes, schools, and storm shelters were also 
evaluated in order to document building performance as well as loss of function 
from Hurricane Katrina. Documentation of observations is presented in this 
report. Photographs and figures are included to illustrate building performance 
in the wind field and surge areas produced by Katrina. The conclusions and 
recommendations of the MATs findings will assist in minimizing damages from 
future hurricanes.