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Homework 8: Hurricane Damage
(adapted from Pipkin et al.)
Tropical cyclones have a significant impact on coastal areas of the world. In the Atlantic Ocean
they are called hurricanes (from Hurican, the Carib god of evil), whereas similar storms in the
Pacific Ocean are called typhoons. They are a significant part of global weather systems because
they transfer large quantities of water and warm, moist air from equatorial regions to higher
latitudes. In the Caribbean Sea, the Gulf of Mexico, and the southeastern United States, hurricanes have shaped low-lying coastal areas and, at times, have caused dramatic losses of life and
property. Even with the use of orbiting weather satellites, hurricane prediction and tracking
remains a major challenge for meteorologists.
Hurricane Generation
The hurricane season extends from June 1 to October 1 in the North Atlantic Ocean. This is because hurricanes get most of their energy from the equatorial oceans in the summer and early
fall, when seawater temperatures are warmest, usually above 25°C (about 800F). Hurricanes
begin as tropical waves, areas of organized clouds 200 - 500 kilometers in diameter (Figure 81), in the eastern equatorial Atlantic. As hot air rises over the warm ocean water, the atmospheric
pressure drops, and cyclonic (counterclockwise) circulation begins, with strong winds rushing
toward the low pressure center. At this point the wave becomes a tropical depression. It
becomes a tropical storm when winds 65 -118 kilometers / hour (39 -74 miles/hour) develop.
If winds exceed 118 kilometers/hour, the storm is called a hurricane (in the Atlantic and eastern
Pacific oceans) or a typhoon (in the western Pacific Ocean).
Figure 8-1 Atmospheric Waves West of Africa
The airflow off of the western Africa in the tropics are unstable during the NH summer creating atmospheric
depressions and sometimes hurricanes that propagate westward.
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Figure 8-2 Hurricane Structure – Satellite View
Tropical storms and hurricanes have cyclonic or counterclockwise circulation in the Northern Hemisphere because
the Coriolis effect deflects the inward air flow toward to the right. In the Southern Hemisphere, the Coriolis
deflection is to the left so that cyclones in the southern tropics have clockwise rotation.
Hurricane Naming
Prior to 1953, hurricanes were named for the year or month of their occurrence, for the writer
who described their passage, or for places sustaining severe damage, like the Galveston
Hurricane of 1900 (Figure 8-3). During World War II, U.S. Navy and Army Air Corps
meteorologists forecasting tropical cyclones in the Pacific Ocean began to informally give
typhoons women's names, probably after their wives or girlfriends. Other naming schemes were
women's names in alphabetical order, and by the international phonetic alphabet-Alpha, Bravo,
Charlie, Delta, Echo, Foxtrot, and so on. In 1953 the U.S. Weather Bureau began to name Atlantic
hurricanes with an alphabetical sequence of female names. The current hurricane-naming method
is one of alternating male and female names, such as the recent names Alberto, Beryl, Chris,
Debby, and so forth. Many names have been retired to the hurricane "Hall of Fame" because
their storms were so devastating-Andrew, Gilbert, and Camille, for example.
Figure 8-3 Galveston Damage - 1900
The 1900 hurricane that hit Galveston Texas completely destroyed the town and killed many of the inhabitants.
Measuring Hurricane Strength
The strength of hurricanes is measured by the Saffir-Simpson scale (Table 8-1), which uses
minimum sustained wind speeds to categorize storms (Figure 8-1) from Category 1, a minimal
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hurricane, to Category 5, the most intense hurricane. Hurricane Mitch, which devastated Central
America, and Hurricane Georges, which struck the coastal United States in 1998, were Category
5 events.
Figure 8-4 Hurricane Saffir Simpson Category - Damage
TABLE 8-1
Since 1944, aircraft have been used to study tropical disturbances that had the potential to develop into hurricanes. Wind speeds and atmospheric pressure changes are measured by technicians in aircraft flown by Air Force personnel, who are called "The Hurricane Hunters" (Figure
8- 5).
Because hurricanes have diameters of hundreds of kilometers and may have dozens of convective storms embedded in them, they may affect coastal areas far from the main storm center.
As they approach the shoreline, NOAA's Hurricane Warning Center in Miami Beach, Florida,
may is-sue a hurricane watch, a 36-hour advance notice of high winds and storm surge, or a
hurricane warning, which means that hurricane winds and surge are expected within 24 hours.
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Figure 8-5 Weather aircraft of the "Hurricane Hunters" flying through the eye of a hurricane. [Photograph
courtesy of the 53rd Weather Reconnaissance Squadron, 403rd Wing, U.S Air Force.]
Hurricane damage is caused by high winds, flooding, and storm surge. Surface winds can cause
an abnormal rise in sea level, reaching from 1 to 6 meters above normal sea level (Figure 8-6).
Along the Gulf Coast, the estimated 330 kilometer/hour winds of Hurricane Camille in 1969
caused a maximum storm surge of 8 meters, with 3-meter-high wind-driven waves atop the
surge. The end result was a l0-meter-high wall of water approaching the Mississippi coastline.
Failure to evacuate caused significant loss of life. One survivor of a "hurricane party" was found
floating on a sofa 8 kilometers further inland from the coastal apartment in which the party was
held.
Figure 8-6 Storm Surge.
(top) A sea level record on Mustang
Island, Texas is partitioned into the
(middle) contribution of storm surge
(atmospheric wind and pressure)
and (bottom) astronomical (sun and
moon). Note the extreme, storm
surge-related high water around
February 1.
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Not all tropical storms develop into hurricanes, and not all hurricanes develop damaging storm
surge. Hurricanes tend to be cyclic; with periods during which relatively weak tropical storms
impact coastlines followed by periods of stronger hurricanes. This is a dangerous sequence,
because coastal residents tend to remember only the most recent tropical storm events.
Hurricane development and strength may be cyclical because El Nino/Southern Oscillation
events (see LAB10) may suppress tropical storms in the Atlantic Ocean, while permitting
stronger storms to approach the west coast of North America.
The relative strength of hurricanes can be assessed from the atmospheric pressure of each storm,
measured in millibars (mb) or millimeters of mercury (mm Hg). Inches of mercury is used in
aviation and in some weather reporting formats (see Table 8-2 for conversions). Minimum
surface pressure, however, is not necessarily a measure of the destructive potential of a
hurricane. The lowest atmospheric pressure ever measured was during Hurricane Gilbert in 1998
in the Caribbean Sea: 888 mb, which is a record low. However, Gilbert was not as destructive as
some other less intense hurricanes because its landfall was onto rising terrain and into less
densely populated areas of the United States and Mexico. Table 8-2 shows the 20 most intense
North American hurricanes since 1900 based on atmospheric pressure in the storm cell. Table 83 lists the most expensive American hurricanes since 1900. For each storm, the damage estimates
have been adjusted to 1996 dollars.
TABLE 8-2
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TABLE 8-3
Movement of Hurricanes
The advance of a tropical storm or hurricane is controlled by the prevailing surface currents of
the equatorial Atlantic Ocean. Tropical storms are moved westward by the North Equatorial
Current, but there is extreme variability in the latitudinal (north-south) location of the storm
track. Tropical cyclones may move through the Caribbean Sea between South America and the
east-west chain of islands east of Cuba and Hispaniola, or they may be deflected north of Cuba
into the Bahamas. Storms approaching the Atlantic coast of North America may be deflected
northward by the Gulf Stream, or their advance may be sufficiently rapid to move them onshore
into Florida or Georgia. Tropical cyclones developing in the Caribbean may move westward to
Central America, or as did Hurricane Mitch in 1998, they may be forced northward across the
Gulf of Mexico by the Loop Current. Since 1949, seven Atlantic hurricanes have crossed into the
eastern Pacific Ocean, becoming Northeast Pacific hurricanes or tropical storms.
Another factor that may influence the advance of tropical storms in the Atlantic Ocean is the
presence of warm or cold weather fronts or cells on the North American continent during the
approach of the storm. Strong clockwise (anti-cyclonic) winds of high-pressure weather cells
may slow the approach of tropical storms, or even stop their approach entirely. Hurricanes
"stalled" in the Gulf of Mexico or the Atlantic Ocean may intensify, degenerate, or be deflected
to the northeast without making any landfall on the North American continent. The unpredictable
nature of hurricane movement is perhaps best shown by the "zig-zag" approach of Hurricane
Elena in September 1985 (Figure 8-7).
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Figure 8-7 Hurricane Elena Trajectory
The track of Hurricane Elena in the Gulf of Mexico during September, 1995. Elena strengthened to hurricane status
in the northern Caribbean Sea between Cuba and Hispaniola, then moved westward until it encountered the Loop
Current in the Gulf of Mexico. The Loop Current deflected the storm to the northeast, where it "stalled" off Florida,
then made a "retrograde" motion nearly due westward across the coastal areas of the Florida Panhandle and
Alabama-before making landfall on the Mississippi coast.
Forecasting of Hurricanes
Because it is so critical to assess the strength of tropical cyclonic storms, the National Oceanic
and Atmospheric Administration (NOAA) operates the National Hurricane Center in Miami,
Florida. The National Hurricane Center distributes tropical weather, hurricane, and severe storm
information to the public by television, radio, and the Internet. Its web site, at
<http://www.nhc.noaa.gov>, contains the latest forecasts for tropical storm activity,
reconnaissance data, and historical storm data for the North Atlantic, Eastern Pacific, Central
Pacific, Western Pacific, and other regions. Another «official" source of information is the
NOAA National Climatic Data Center, which contains information on hurricanes, El Nino,
global climate, and other weather data. The NCDC has images and movies of hurricanes,
tropical storms, typhoons, and other severe storms at <http://www.nodc.noaa.gov/ol/
satellite/oIimages.html>. Other web sites providing hurricane information and graphics are
listed in the Bibliography.
REFERENCES
Pipkin, B.W., D.S. Gorsline, R.E. Casey, D.A. Dunn & S.A. Schellenberg, “Laboratory
Exercises in Oceanography”, 3rd Edition, W.H. Freeman & Co., 2001. (LEiO)
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EXERCIZE 8-1 HURRICANE DAMAGE
1. Compare hurricane strength (storm category and atmospheric pressure) to hurricane damage
using the information in Tables 8-2 and 8-3.
TABLE 8-2
TABLE 8-3
(a) Is there a relationship between strength and damage? ___________
If so, describe it.
(b) Does a Category 5 storm always produce more damage than a Category 4 storm?______
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What 2 storms?
(c) Is there a predictable relationship between storm damage and meteorologically measurable
data (wind speed, storm category, atmospheric pressure)?________________
If so, describe it.
(d) What factors could produce more damage from a "weaker" hurricane?
EXERCIZE 8-2 HURRICANE EROSION
1. A beach profile survey was conducted prior to the landfall of a hurricane called Zeke. These
data (Table 8-6) show the beach elevation (relative to mean sea level) versus the distance
offshore relative to a starting point "benchmark".
Plot these data on the graph on the following page.
TABLE 8-6
TABLE 8-7
(a) Plot the "post-hurricane' beach profile survey data in Table 8-7 on the same graph as in
question 4 using a different color.
(b) What effect did the hurricane have on the position of the shoreline and the profile of the
beach? Where was sand eroded from, and to where was this eroded sand moved?
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EXERCIZE 8-3 HURRICANE SURGE
1. The Hurricane Camille storm surge (see Table 8-8 data) inundated coastal area of Mississippi
in 1969 – see the map in Figure 8-9, with place names numbered and survey stations labeled.
The data from Table 8-8 have been transferred to Figure 8-9 - an east-west profile along the
coastline, depicting storm surge height along coastal Mississippi.
TABLE 8-8
(a) Since the highest wind stresses in a cyclonic storm will be in the northeast quadrant of the
storm, does the maximum storm surge height give you information on the landfall of the eye
of Hurricane Camille? ________________________
Explain.
(b) Before the storm, Ship Island was one continuous east-west-trending barrier island. Does
the post-storm condition of Ship Island provide any information about the storm's track and
its landfall?__________________________
Explain.
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Figure 8-8
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