NOAA Technical Memorandum NWS SR-206
(Updated Through 2002)
ATLANTIC TROPICAL STORMS AND HURRICANES AFFECTING
THE
UNITED STATES: 1899-2002
Donovan Landreneau National Weather Service Office Lake Charles, Louisiana
1. Introduction
Tropical storms and hurricanes have affected
every coastal state along the Atlantic and Gulf of Mexico from Texas to Maine.
Even some inland states, such as Arkansas and Tennessee, have adversely
experienced the effects of such storms. Anyone living in the eastern half of the
U.S. should be aware of the effects of tropical storms and hurricanes, and how
they could affect their lives and businesses.
This study was initiated for the purpose of
addressing such concerns and others like them. By using a large part of
the work done by Neumann, et al. (1993), several statistics are revealed,
including frequency and return period of tropical storms and/or hurricanes which
have affected the various coastal and inland states. The distance between
landfalls for hurricanes is introduced to show which coastal state has the most
concentration of landfalls over time, rather than just looking at which state
has the highest number of landfalls.
2. Data Collection
The majority of the information used for this
study came from Neumann, et al. (1999). The Atlantic track file (Jarvinen, et
al. 1984) was used to complement this publication. Additional data for the years
1999-2002, as well as an updated Atlantic track file through 2002, were
obtained from the National Hurricane Center Web site. Tropical
depressions were excluded from this study due to the absence of data for these
weak tropical systems.
Information on coastline length was obtained
from Famighetti (1996). During the process of measuring the coastline,
Connecticut was eliminated and had no measurement of a coastline. A CD-ROM
mapping program, DeLorme (1997), was used to estimate a coastline length for
Connecticut.
3. Analysis and Results
Hurricanes are ranked according to strength and
by the amount of damage they cause.
Table 1 is a brief description of the Saffir/Simpson hurricane intensity scale. The weakest hurricane is
designated a Category One with a maximum sustained wind from 74 to 95 mph and an
average storm surge of 4 to 5 ft above sea level. In contrast, a Category Five
hurricane has a maximum sustained wind greater than 155 mph and a storm surge of
greater than 18 ft. Storm depends on many factors such as the shape of the
continental shelf just offshore, whether the hurricane makes
landfall at high or low tide, and the location of the onshore and offshore winds
relative to the eye of the hurricane.
Appendix A is a chronological list of hurricanes
of various intensities which have struck from Texas to Maine for the
years 1899-2002. In this study, a storm affects a state only once. For
example, Hurricane Erin of 1995 made landfall on the east coast of Florida,
moved over the peninsula, and struck the Florida panhandle two days
later. Such situations are counted once for simplicity since it was the same
storm. Table 2 further divides these direct hits according to category using the Saffir/Simpson scale. As one would expect, Category One hurricanes have struck
most frequently with 63 landfalls, and Category Five storms are rare with
only three landfalls. Notice the secondary maximum of Category Three
landfalls.
The Glossary of Meteorology (Huschke 1959) and
Elsner and Kara (1999) define frequency as the number of times a specified event
occurs in a given series of observations, or period of time. In Table 2, the
landfall frequency is represented by dividing the number of storms which made a
landfall or direct hit by time. In this case, the time is 104 years. With
the exception of the total for the United States, the results for each state
are smaller than one, since no state averages a hurricane landfall or direct
hit every year. The frequency of 1.62 for the United States signifies an average
of one to two hurricane landfalls per year, somewhere along the Gulf or
Atlantic coastline.
The above references define return period as the
average time interval between the occurrence of a given quantity and that of an
equal or greater quantity. This would represent the reciprocal of frequency, or
the average number of years between each hurricane landfall. Table 2 shows, for
example, that the average number of years between a hurricane landfall
for Louisiana is 3.9. In contrast, the average number of years between landfalls
in Georgia is 20.0. This gives an idea of the climatological average.
Table 2 also gives information on the
coastline length of each state and the distance between each hurricane
landfall. We assume storms are, on average, distributed randomly along the
coast, and we obtain this figure by dividing the state's coastline length by the
number of hurricanes which have affected that state. This value is introduced to
show the concentration of landfalling hurricanes for each state. The smaller the
number, the smaller the distance between each landfall resulting in a greater
concentration of landfalls over time. For example, the total coastline length
for Texas is 367 mi. Dividing this figure by the total number of hurricane
landfalls, in this case 37, gives the distance between landfalls of 9.9 mi.
Alabama, on the other hand, only had 11 hurricane landfalls during this time
period. Since its coastline is only 53 mi, the resulting distance between
landfalls is 4.8 mi, a higher concentration than Texas. The relative numbers for
states should be used with some caution, however, because the assumption of
random distribution may not be valid. Portions of the Atlantic and Gulf coasts
of Florida, for instance, may have significantly different landfall
frequencies.
A tropical storm has maximum sustained winds of
39 to 73 mph. In this analysis, a tropical storm is considered to have
affected a state if the center of the storm intersected any portion of the
state while the storm was at tropical storm intensity. This does not include
periphery effects from storms affecting adjacent states or countries. To obtain
these data, a very detailed analysis of each track was performed using
the yearly track charts (Neumann, et al. 1999) in conjunction with the Atlantic
track file (Jarvinen, et al. 1984). The results are shown in
Appendix B.
Using the results in Appendix B,
Table 3 was
constructed to represent the total number of tropical storms which have affected
each state, along with the frequency and return period. The methodology for
computing frequency and return period is the same as Table 2, except each hit
represents a tropical storm passing through any part of the state, and not just
a coastal landfall. Table 4 shows the number of landfalling hurricanes and
tropical storms which have affected each coastal state, along with the
frequency and return period. Once again, the methodology for computing frequency
and return period is the same as Tables 2 and 3.
4. Summary
The main purpose for this study is to
show which states are more susceptible to tropical storms and hurricanes by
using frequency of occurrence and the return period. The distance between
landfalling hurricanes was introduced to compare which states have the most
concentration of landfalls, or in other words, the smallest average distance
between landfalls over the 104-year data span. I emphasize again, however, that
the length of a state's coastline plays a significant role in the likelihood of
a land-falling storm (i.e., exposure), and a longer coastline decreases the
possibility that land-falling storms will strike with equal likelihood along all
parts of the coast. The latter is especially true for Florida and Texas (Elsner
and Kara 1999).
Over the years, certain cycles and patterns of
tropical cyclones affecting coastal states can be observed. Such patterns
include periods when most of the storms made landfall along the east coast of
the U.S. verses the Gulf coast, during El Ni�o/La Ni�a events, etc. Such
distinctions were not attempted in this paper, as many NWS offices within the
studied area have performed local studies to address these issues. The
subject is also well covered in many published papers and texts, see for example
Elsner and Kara (1999) and its references.
Results presented in this study represent
averages, and are not intended for use as a forecast of when the next tropical
storm or hurricane will affect a state. Instead, they may serve as a general
tropical cyclone climatology for coastal states as well as some inland states as
noted in this analysis.
5. Acknowledgments
The author would like to thank the many authors
and editors of the various publications used in this study, especially Neumann,
et al. (1993), without which this analysis would have been close to
impossible to complete. Many thanks also go to Lee Harrison (MIC) and Ken Falk
(SOO) of WFO Shreveport, as well as Steve Rinard (MIC) of WFO Lake Charles
for allowing time to complete this project and reviewing the format and content
of this paper.
6. References
DeLorme, 1997: Street Atlas USA. Vers.
3.0. CD-ROM Computer Software.
Elsner, James B. and A. Birol Kara, 1999:
Hurricanes of the North Atlantic - Climate and Society. Oxford University
Press.
Famighetti, Robert, 1996: The World Almanac
and Book of Facts. 1997 ed.
Huschke, Ralph E., 1959: Glossary of
Meteorology. American Meteorological Society, Boston, MA.
Jarvinen, Brian R., Charles J. Neumann, and Mary
A. S. Davis, 1984: A Tropical Cyclone Data Tape for the North Atlantic Basin,
1886-1983: Contents, Limitations, and Uses. NOAA Technical Memorandum
NWS-NHC-22.
Neumann, Charles J., Brian R. Jarvinen, Colin J.
McAdie, and Joe D. Elms, 1999: Tropical Cyclones of the North Atlantic Ocean,
1871-1998. Historical Climatology Series 6-2, Asheville, North Carolina,
National Climatic Data Center.
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