3498 JOURNAL OF CLIMATE VOLUME 20

Spatiotemporal Patterns and Return Periods of Tropical Storm and Hurricane Strikes from Texas to Maine

BARRY D. KEIM AND ROBERT A. MULLER Louisiana Office of State Climatology, and Department of Geography and Anthropology, Louisiana State University, Baton Rouge, Louisiana

GREGORY W. STONE Coastal Studies Institute, and Department of Oceanography and Coastal Sciences, Louisiana State University, Baton Rouge, Louisiana

(Manuscript received 25 April 2006, in final form 23 October 2006)

ABSTRACT

The authors analyze 105 yr (1901–2005) of strikes at 45 coastal locations from Browns- ville, Texas, to Eastport, Maine, with the primary objective of examining spatiotemporal patterns of storm activity. Interpretation of the data suggests that geographically, three focal points for activity are evident: south Florida, the Outer Banks of North Carolina, and the north-central Gulf Coast. Temporally, clusters of hyperactivity are evident in south Florida from the 1920s through the 1950s and then again during the most recent years. North Carolina was a region of enhanced activity in the 1950s and again in the 1990s. A more consistent rate of occurrence was found along the north-central Gulf Coast; the last two years, however, were active in this region. Return periods of tropical storm strength systems or greater range from a frequency of once every 2 yr along the Outer Banks of North Carolina, every three years on average in southeast Texas, southeastern Louisiana, and southern Florida, and about once every 10–15 yr in northern New England. Hurricane return periods range from 5 yr in southern Florida to 105ϩ years at several sheltered portions of the coastline (e.g., near Cedar Key, Florida, Georgia, and the northeastern seaboard), where some locations experienced only one strike, or no strikes through the entire period of record. Severe hurricane (category 3–5) return periods range from once every 15 yr in South Florida to 105ϩ in New England.

1. Introduction leans, Louisiana; and even New York, New York), and residential areas. For society to better cope with, and Tropical storms and hurricanes are among the most plan for these events, it would be advantageous to un- media-focused environmental hazards (Unger 1999). derstand the frequency and magnitude of tropical These events, especially major hurricanes such as An- storms and hurricanes at or near the cities in question drew or Katrina, result in catastrophic losses of life and along the coast. property, they interrupt commerce, and they frequently One of the earlier efforts to produce hurricane return cause dramatic geomorphic change within the coastal periods was provided by Simpson and Lawrence (1971), zone. Most societal impacts of tropical storms and hur- based on hurricane strikes from 1886 to 1970. They ricanes, however, are restricted to rather narrow zones analyzed strikes and return periods for all hurricanes along the coast, including major recreational beach re- and major hurricanes within 80-km coastal segments. sorts (i.e., Myrtle Beach, South Carolina; Ocean City, For all hurricanes (categories 1–5), return periods Maryland; and Pensacola, Florida), bays and lagoons, ranged from 6 years in southeastern Florida to 85 or estuarine locations, ports (i.e., Miami, Florida; New Or- more years (no strikes at all) along coastal segments in Georgia, New Jersey, and along the New England coast. A more recent effort was presented by Elsner Corresponding author address: Barry Keim, Department of Ge- ography and Anthropology, Louisiana State University, Baton and Kara (1999) based on strikes from 1900 to 1996. Rouge, LA 70803. They focused on return frequencies along the coast for E-mail: [email protected] each county. Hurricane return periods (all categories

DOI: 10.1175/JCLI4187.1

© 2007 American Meteorological Society

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1–5) ranged from 4 years for Monroe County, Florida places are not evenly spaced along the coast, but in- (Florida Keys), to 97ϩ years in Georgia and Maine. stead, places were selected that are well known region- However, the estimated return periods were somewhat ally as cities, or famous beach resorts along barrier is- affected by the varying lengths of coastline in each lands. Better-known inland cities are also noted in the county. For example, the coastline of Monroe County figure legend, where appropriate. We anticipate that extends approximately 275 km from Key Largo to Ev- return periods will be similar, but somewhat longer for erglade City. In contrast, Charlotte County, Florida, a single point than for 80-km segments of coast, or for also located in southern Florida on the Gulf Coast, has the coastline of an entire county. a coastline of only 19 km. Without accounting for the To evaluate storm strikes at various places along the varying lengths of coastline, the aforementioned ap- coast, we needed to adapt standard estimates of the proach is biased toward giving longer county coastlines average sizes of storms by intensity. Dunn and Miller more opportunity to experience an event, thereby re- (1960), Simpson and Riehl (1981), and Merrill (1984) ducing the length of the return periods. all agree that there is considerable variability in the size In this paper, we present a point-based analysis that of tropical storms and hurricanes, and spatial dimen- removes this bias. Although there is utility in these pre- sions are not well correlated with storm intensity. Cat- vious research efforts and their applications, we con- egory-5 storms can be large or small, and this is also tend that an analysis of tropical cyclone return periods true for significantly weaker tropical storms. Pielke and at specific points, rather than sectors or county-length Pielke (1997) provided examples of the varying sizes segments of coastline, yields results with even greater and diameters of storms, and display the tendency for utility for local building codes. Furthermore, results storm conditions to extend farther to the right than the from this study are more applicable to understanding left of the storm focal point (eye) along the storm track the hurricane climatology and its geographic variability (Fig. 2). The above studies, however, suggest that for an along the East and Gulf Coasts of the . “average” hurricane, hurricane-force winds extend for- The objectives of this research are as follow: ward and to the right about 50 to 100 km from the eye 1) To investigate tropical storm and hurricane strikes and 25 to 50 km to the left. for specific coastal places (towns or cities) rather From these estimates of storm properties, coastal than sectors of the coasts storm conditions can be generalized by storm catego- 2) To depict the geographical and temporal patterns ries, while taking into account that Northern Hemi- (1901–2005) of tropical storm and hurricane strikes sphere storms are more extensive and severe on the along the entire East and Gulf Coasts of the United right side of the storm and less developed on the left- States hand side. Our model, depicted in Fig. 3, is a relatively 3) To calculate return periods for tropical storms, hur- conservative representation of average-size storms. The ricanes, and severe hurricanes model assumes that with tropical storms, tropical- This spatiotemporal approach is an extension of storm-force winds extend 80 km to the right and 40 km Muller and Stone (2001) by increasing its temporal (up- to the left of the track. For category-1 or -2 hurricanes, dated from 2000) and geographical extension (from hurricane conditions are assumed to extend 80 km to , North Carolina, to Maine) of tropical the right, and tropical storm conditions an additional 80 storm and hurricane strikes. The combination of a geo- km to the right, with hurricane conditions 40 km to the graphical and temporal analysis provides a unique pic- left and tropical storm conditions an additional 40 km ture of when and where certain portions of the coastline to the left. Similarly, for major category-3–5 hurricanes, were most active with respect to tropical storms and major hurricane conditions are assumed to extend 80 hurricanes. This research may also shed some light on km to the right, weaker hurricane conditions an addi- the debate surrounding the impacts of global warming tional 80 km to the right, and tropical storm conditions and the Atlantic Multidecadal Oscillation (AMO) on another 80 km to the right, with the respective incre- landfalling tropical storms and hurricanes. ments of 40 km each to the left. Hence, for storm strike identification at the 45 points, tropical storms represent a swath 120 km wide along a coast perpendicular to the 2. Methods storm track, category-1 or -2 hurricanes represent a We examined temporal and geographical variability hurricane swath 120 km wide with tropical storm con- in tropical storm and hurricanes strikes at 45 places ditions an additional 80 km to the right and 40 km to along the Gulf of Mexico and Atlantic Coasts of the the left. For major hurricanes the hurricane intensity United States from Texas to Maine (Fig. 1). These swath is 240 km wide, again with tropical storm condi-

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FIG. 1. Locations of the 45 coastal cities along the Gulf and East Coasts of the United States used in this study. tions an additional 80 km to the right and 40 km to the were within 80 km of the coastline. This is consistent left. with our model in Fig. 3 where estimated storm condi- The model is applied to tropical storm and hurricane tions extend outward and forward in the right-front tracks and intensities taken from the 6-hourly data from quadrant 80 km. This identification of strike intensity at the National Hurricane Center (NHC) for each storm; the coastal sites tends to be a conservative estimate of these data are available on several Web sites (i.e., www. storm impacts because of very destructive storm surges wunderground.com/tropical/). Strike intensities at the that are generated by storm intensities well offshore. A 45 coastal locations are estimated from reported maxi- tragic example is the record 28-ft storm surge at Bay St. mum sustained winds when approaching centers Louis, Mississippi, during Hurricane Katrina; at landfall

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FIG. 2. Range in sizes of representative hurricanes. Modified from Pielke and Pielke (1997). in Mississippi, Katrina was classified a category-3 enough to coastal communities to fall within the con- storm, but the record surge obviously was a response to straints of the model noted above. The record for tropi- its category-5 status for 24 h when the eye of the un- cal cyclones in the North Atlantic Basin dates back to usually large Katrina was 250 km and 24 h from landfall the nineteenth century (Neumann et al. 1993) and even (Knabb et al. 2005). In this same report, the authors earlier (i.e., Ludlum 1989). However, this record has state that between 1986 and 2005 all 11 hurricanes ap- large inhomogeneities over time, which complicates in- proaching the central Gulf Coast with minimum pres- terpretations of long-term trends and variability in fre- sure less than 973 mb weakened significantly during the quencies and intensities (Solow and Moore 2002). Em- final 12 h before landfall. For example, Hurricane Lili pirical observations of pressure provide a fairly reliable off the Louisiana coast in 2002 was a category-4 storm record of landfalling storms in the United States back when the center was approximately 250 km off the to around the turn of the twentieth century (Landsea et coast. Within 100 km of the coast, Lili had rapidly al. 1999). As a result, our dataset begins in 1901 and weakened to a category-2 storm, before making landfall extend through 2005. as a category 1. More recently, Hurricane Rita also weakened substantially before making landfall in west- 3. Spatiotemporal strike patterns ern Louisiana during the 2005 season. The focus of this analysis is primarily on landfalling The National Hurricane Center dataset listing tropi- tropical cyclones, or at least those that traversed close cal and hurricanes tracks for the entire Atlantic Basin

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FIG. 3. Dimensions of the tropical storm and hurricane strike model. includes 421 tropical storms and 555 hurricanes, a grand Wrightsville Beach to Nags Head. Two intervening total of 976 cyclones for the 105 yr between 1901 and coastal sections exist with noticeably fewer strikes from 2005 (www.wunderground.com/tropical/). For each Apalachicola, Florida, southeastward to south of Cedar storm track, pressure, wind speed, Saffir–Simpson cat- Key, Florida, on the Gulf Coast, and on the Atlantic egory, and latitude–longitude are given at 6-h intervals. Coast from northern Florida northeastward to include The same dataset also provides Saffir–Simpson catego- most of the Georgia coast and centered especially on St. ries at landfalls in the continental United States. For Simons Island, in the vicinity of Brunswick, Georgia. these years, the dataset shows 354 landfalls, 176 at From Virginia Beach northeastward, tropical cyclone tropical storm status, 111 category 1 or 2, and 67 major strikes become increasingly uncommon, except for a hurricanes, categories 3–5. Our analysis of strikes at the modest increase along the more-exposed coasts of east- 45 coastal locations includes 194 individual tropical ern Long Island (Montauk Point), Rhode Island (New- storms, 117 category-1 and -2 hurricanes, and 57 major port), and Cape Cod (Chatham). The model indicates hurricanes for a grand total of 368 storms, 14 more than no major (category-3 and above) hurricane strikes in the National Hurricane Center dataset. The reason north of Cape Hatteras, no hurricane strikes at Ocean for the discrepancy stems from storms that tracked near City, Maryland, and only one hurricane strike, in 1903, the coast, but did not make landfall. Our analysis in- at Atlantic City and Sandy Hook in New Jersey. Be- cludes those storms that grazed the coast and fell within cause storm tracks are most often northeastward and the domain of our model, but were not counted as land- parallel with the coast north of Cape Hatteras, in Fig. 4 falls by the National Hurricane Center. it is evident that the same storm can result in strikes at Using the criteria noted above, Fig. 4 provides a many coastal locations for more than 1500 km from unique assessment of tropical storm and hurricane Cape Hatteras to Eastport, Maine. Notable examples strikes along the Gulf and Atlantic Coasts by merging include the 1943 hurricane, 1954 Hurricane Carol, 1960 time, geography, and storm intensity. Based on these 45 Hurricane Donna, 1996 , and 1999 time series, there are three broad geographical areas Hurricane Floyd. Although hurricane frequencies de- that are highly active: 1) the northern Gulf Coast from crease northward from Cape Hatteras there is an in- Galveston, Texas, to Panama City Beach, Florida, 2) creasing frequency of potentially damaging winter and south Florida from Marco Island on the Gulf Coast spring midlatitude cyclones, or nor’easters; often 10 to around to Vero Beach on the Atlantic Coast, and 3) 20 per season (i.e., see Hirsch et al. 2001). North Carolina, especially the Outer Banks, from In Fig. 4 the most dramatic interdecadal variability

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FIG. 4. Time series from 1901 to 2005 of tropical storm, hurricane, and severe hurricane strikes by location. has occurred in southern Florida on both east and west Florida. Figure 4 also shows how active the Central coasts; Vero Beach on the Atlantic around to St. Pe- Gulf and Florida coasts have been in 2004 and 2005. tersburg and Cedar Key on the Gulf of Mexico. There The dataset in its totality depicts a temporal pattern is clustering of events for the 25 yr between the mid- beginning in the mid-1920s, extending into the mid- 1920s and 1950, and several events during the mid- 1960s, that was very active for landfalling storms in the 1960s. However, with the exception of Hurricane An- United States. A relatively inactive period is evident drew in 1992, there are almost no hurricane strikes, and from the mid-1960s through the mid-1990s, which again only a few tropical storm strikes over the most recent 40 becomes active from 1995 to 2005. These patterns ap- yr until 2004 and 2005. Along the Outer Banks of North pear consistent with documented fluctuations in the Carolina, there has also been two temporal clusters of AMO (Elsner 2006; Vermani and Weisberg 2006), strike events, in the 1950s and again in the 1990s, with though the longevity and destructiveness of storms as relatively few strikes in between. Figure 4 also suggests noted by Emanuel (2005) is not taken into consider- that there are clusters of strikes in one region that may ation here. However, despite the fact that U.S. landfall- be associated with infrequent strikes in adjacent re- ing hurricanes only comprise 25% of North Atlantic gions. Examples include the clusters of strikes in south- hurricanes and 3% of global hurricanes (Curry et al. ern Florida, 1903–10, 1924–50, and 1964–67, as con- 2006), these results seem consistent with Landsea trasted to infrequent strikes along the eastern half of (2005). the northern Gulf Coast for the same runs of years. Similarly, the clusters of strikes along the Outer Banks 4. Storm return periods of North Carolina during the 1950s and 1990s can be Return periods at the 45 coastal locations for the contrasted with very inactive years over southern 105-yr period (1901–2005) are rounded to the nearest

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FIG. 5. Average return periods for tropical storms, hurricanes, and severe hurricanes (category 3–5). year (Fig. 5). These average return periods are derived represented in the inner tier; the middle tier for all by dividing the 105-yr period of record by the total hurricanes; the outer tier only for major hurricanes— number of strikes at the respective locations. We ac- categories 3, 4, and 5. Tropical cyclone return periods knowledge, however, that any location can have mul- are as low as once every 2 yr on the average along the tiple strikes in one year, and none for several consecu- Outer Banks of North Carolina, once every 3 yr along tive years, and the variations in the number of storms the north-central Gulf Coast as well as in southern per annum can easily be modeled using the Poisson Florida from Cocoa Beach to St. Petersburg. Tropical distribution. cyclone return periods are 10 yr or more in southern In Fig. 5, return periods for all tropical cyclones are Georgia, New Jersey, and northern New England.

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For all hurricanes, return periods are shortest, about ods of record differ in the three respective studies 5 yr, in southern Florida from Palm Beach to Key West, (1901–2005, Keim et al.; 1900–96, Elsner and Kara; and and the Outer Banks of North Carolina, and 10 yr or 1886–1970, Simpson and Lawrence). The common pe- less along the northern Gulf Coast from Galveston riod for the three studies is the 70 yr between 1901 and eastward to Apalachicola with the exception of a 15-yr 1970. Simpson and Lawrence include a 15-yr period return period at Cameron, in southwestern Louisiana, between 1886 and 1900, when hurricane activity was 5.7 just east of where Hurricane Rita made landfall in 2005. yrϪ1, slightly above our long-term average of 5.3 yrϪ1 Less-frequent hurricane strikes and much longer return between 1901 and 2005, and excludes the 35 yr begin- periods are evident along the northeastern Gulf of ning with 1971 when the average was 6.1 yrϪ1. Elsner Mexico in the vicinity of Cedar Key, Florida (35 yr), and Kara do not include the 9 yr between 1997 and and 52 yr at St. Simons Island on the coast of Georgia, 2005, when the landfall average was especially high at with both coastal regions often sheltered from direct 8.2 hurricanes per year. Additionally, for locations with storm strikes by the configurations of adjacent coast- infrequent strikes, one new strike changes the return lines. North of Nags Head, North Carolina, return pe- period substantially; for example, one strike between riods for all hurricanes range between 21 and 35 yr at 1901 and 1999 yields a return period of almost 100 yr, the more exposed locations between Jones Beach, near whereas a second strike in 2000 reduces the return pe- the western end of Long Island, and Chatham, Massa- riod to 50 yr. Because of the differences between the chusetts, on Cape Cod. Return periods extend to 52 or study periods, Simpson and Lawrence (1971) show re- more years at more sheltered locations in this region. turn periods that are slightly longer, with a few excep- Our strike model indicates no hurricane strikes at tions, than for the two more recent studies. Ocean City, Maryland, for the 105-yr record starting Given that our dataset covers a more similar time with 1901. span to Elsner and Kara (1999), we restrict compari- For major hurricanes, return periods are shortest, 13– sons to all hurricane strikes in these two studies. For the 18 yr on average, in southern Florida from Marco Is- 45 points, our return periods are longer than Elsner and land on the Gulf to Palm Beach on the Atlantic, and 21 Kara at 26 locations, the same at 5, and shorter at 14. to 26 yr from Galveston eastward to Pensacola Beach; Having more locations with longer recurrence intervals exceptions to these patterns are at Cameron and Gulf- in our study was expected because our point analysis is port, which is somewhat protected by the delta of the a smaller target than an entire county length of coast- Mississippi River. Major hurricane return periods are line. For the 33 locations where our return periods are 35 yr at both Cape Hatteras and Wrightsville Beach in 26 yr or less, four hurricane strikes in 105 yr, we average North Carolina. The strike model indicates no major hurricane strikes during the 105 yr period at Port Aran- 1.3 yr longer than Elsner and Kara (1999), more than sas, Texas (Corpus Christi), Apalachicola, Florida, 10% longer. Almost all of the locations where our re- from Cocoa Beach, Florida, northward to Tybee Beach turn periods are shorter (more frequent storms) than (Savannah), Georgia, except at Jacksonville Beach, and Elsner and Kara (1999) occur along the northern Gulf from Nags Head, North Carolina, to the Canadian bor- of Mexico and southern Florida where there were more der. Although the National Hurricane Center has re- frequent hurricane strikes between 1997 and 2005. We ported that the Hurricane of 1938 came ashore in New also compute longer return periods at all of the loca- England as a category 3 (http://www.nhc.noaa.gov/ tions north of Nags Head, where Elsner and Kara pastint.shtml), the 6-hourly data show that the storm (1999) identify more frequent strikes than we found “weakened” to less than category 3 approximately 500 using our model. km prior to landfall, to a category-2 hurricane approxi- The application of the return-period data for future mately 200 km out, and then to a category-1 storm tropical storm and hurricane strikes assumes stationar- shortly after making landfall. Based on these data, we ity—a more-or-less random distribution of strikes conclude that this hurricane made landfall as a minimal through the decades. However, perusal of the temporal hurricane, though the system generated a surge indica- patterns of strikes for individual places in Fig. 4 indi- tive of a much stronger storm (Zielinski and Keim cates significant variability through the decades. In ad- 2003), similar to the large storm surge associated with dition, there is strong suggestion that the recent pattern Hurricane Katrina. of enhanced storm frequencies, beginning in 1995, may A comparison of hurricane return periods as pre- persist for another decade or more (Goldenberg et al. sented in the present study with Elsner and Kara (1999) 2001) as it is probably related to the shifts in Atlantic and Simpson and Lawrence (1971) shows modest dif- sea surface temperature and surface pressure anomalies ferences between datasets (Fig. 6). Note that the peri- over multidecadal time scales (Landsea et al. 1999).

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FIG. 6. Comparison of this study to Elsner and Kara (1999) and Simpson and Lawrence (1971).

5. Tropical hazard index but also on the type and density of development being exposed to storm winds, and with tropical storms and It is generally accepted that wind power increases hurricanes, storm surge is usually the most destructive nearly as a cubic function of wind speed (Stadler and component of the storms. Furthermore, even the threat Hughes 2005). As a result, even modest increases in of a landfalling storm can cause major disruptions in wind speed (of only a few percent) can result in dra- coastal communities in the form of preparation of matic increases in potential storm damage (Dorland et homes for the storm, loss of electricity, and phone ser- al. 1999). Realized damage, however, is not only depen- vice, business closings, as well as evacuations. Using dent upon wind speed, wind duration, and wind power, these basic principles of wind and potential wind and

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FIG. 7. THI by location. Index is derived as sum of all storms from 1901 to 2005, where a tropical storm strike is awarded two points, a category-1–2 hurricane receives four points, and a category 3–5 hurricane is awarded eight points. surge damage, compounded by the level of disruption relative index for the total exposure of a coastal com- to society, a simple tropical hazard index (THI) is de- munity to storms, taking into account both the fre- veloped to provide an additional geographic perspec- quency and intensity of storms. We fully realize the tive on the vulnerability of the Atlantic and Gulf Coast exponential component of potential wind damage as regions. For the entire 105-yr period of analysis, strikes wind speeds increase; however, given the total disrup- of tropical storm intensity are assigned two points, cat- tion caused by storms (including preparation, damage, egory-1 and -2 hurricanes four points, and major hur- and other inconveniences), we feel that a weak hurri- ricanes (categories 3–5) eight points. This provides a cane represents twice the nuisance of a tropical storm,

Unauthenticated | Downloaded 10/07/21 02:39 AM UTC 3508 JOURNAL OF CLIMATE VOLUME 20 and severe hurricane is twice the inconvenience of a time, geography, and storm intensity. It also provides a weaker hurricane. We chose two, four, and eight points potentially important operational baseline for assessing rather than one, two, and four so that summed totals return periods of tropical cyclones along the Gulf and over 100 would stand out to denote exceptional loca- Atlantic Coasts. One of the primary differences be- tions. We stress that the THI represents a very simple tween this research and that of Elsner and Kara (1999), comparative geographical index of the storm hazards and Simpson and Lawrence (1971), is that our study among coastal regions, and the THI should neither be incorporated an analysis of geographical points (mostly related to specific sites along the coasts nor to any one famous beaches) rather than segments (e.g., county of the environmental and socioeconomic impacts lengths) of coastline. Our data also suggests that the (Pielke and Pielke 1997). active period of hurricanes from the late 1920s through THI values range from highs of 152 at Key Largo, the mid-1960s, and again from 1995 to 2005, likely has Florida, and 150 at Cape Hatteras, and 130 at Booth- an association with positive anomalies in sea surface ville, south of New Orleans. In terms of tropical storm temperature and the Atlantic Multidecadal Oscillation and hurricane strikes, the count at Cape Hatteras is 47, mode. In addition, this study also depicts temporal at Boothville 41, and Key Largo only 35. The highest shifts in favored landfall areas, that is, in south Florida THI at Key Largo results from its exposure to major from the late 1920s to 1950, North Carolina in the hurricane strikes, eight, mostly coming westward from 1950s, and south Florida during the early 1960s. The the Atlantic and Caribbean, and the very warm water increase in frequency and intensity of events beginning offshore. Cape Hatteras is very exposed to the tracks of in 1995 is also evident, with a penchant for North Caro- tropical storms and hurricanes moving around the west- lina early in this period, as well as the north-central ern margins of the subtropical, high, but Gulf Coast and the central coasts of the Florida penin- somewhat cooler surface waters help to diminish the sula in the latter portion. The estimated return periods intensity of these tropical cyclones as they progress into that are derived from these 45 time series should also middle latitudes. Boothville is also in an exposed warm- have utility for purposes of planning within these water location on the northern coast of the Gulf of coastal communities. Mexico, but many strikes here are due to tropical storms and category-1 and -2 hurricanes that develop REFERENCES over the southern Gulf of Mexico, often without op- portunities to further intensify during the shorter tracks Curry, J. A., P. J. Webster, and G. J. Holland, 2006: Mixing poli- over the Gulf to landfall. In South Florida from Sanibel tics and science in testing the hypothesis that greenhouse warming is causing a global increase in hurricane intensity. Island around to Vero Beach, THI values are all over Bull. Amer. Meteor. Soc., 87, 1025–1037. 100, as are all four North Carolina places, as well as Dorland, C., R. S. J. Tol, and J. Palutikof, 1999: Vulnerability of along the central Gulf Coast from Galveston, Texas, the Netherlands and northwest Europe to storm damage un- eastward to Destin, Florida, with the unexplained ex- der climate change. Climatic Change, 43, 513–535. ception of Cameron, Louisiana, where the THI is 84, Dunn, G. E., and B. I. Miller, 1960: Atlantic Hurricanes. Louisiana increased in 2005 by the major Hurricane Rita strike. State University Press, 326 pp. The lowest THI values (20) occur along the Maine Elsner, J. B., 2006: Evidence in support of the climate change– Atlantic hurricane hypothesis. Geophys. Res. Lett., 33, coast (Fig. 7), and all of the places northward from L16705, doi:10.1029/2006GL026869. Ocean City, Maryland, have THI scores less than 50, ——, and B. Kara, 1999: Hurricanes of the North Atlantic: Climate due to the obvious impacts of cooler ocean waters on and Society. Oxford University Press, 488 pp. storm intensities at these middle-latitude locations. Emanuel, K., 2005: Increasing destructiveness of tropical cyclones Other places with lower THI scores include sheltered over the past 30 years. Nature, 436, 686–688. portions of the coastlines as they relate to the preferred Goldenberg, S. B., C. W. Landsea, A. M. Mestas-Nuñez, and W. M. Gray, 2001: The recent increase in Atlantic hurricane parabolic shape of storm tracks around the Bermuda activity: Causes and implications. Science, 293, 474–479. high over the North Atlantic (see Neumann et al. 1993). Hirsch, M. E., A. T. DeGaetano, and S. J. Colluci, 2001: An east These places include Atlantic City (22) and Sandy coast winter storm climatology. J. Climate, 14, 882–899. Hook, New Jersey (26), St. Simons Island, Georgia Knabb, R. D., J. R. Rhone, and D. P. Brown, 2005: Tropical cy- (44), and Cedar Key, Florida (66). clone report, Hurricane Katrina, 23–30, August 2005. Na- tional Hurricane Center, 43 pp. Landsea, C. W., 2005: Hurricanes and global warming. Nature, 6. Summary and conclusions 438, E11–E13. ——, R. A. Pielke Jr., A. M. Mestas-Nuñez, and J. A. Knaff, 1999: This paper provides a unique view of tropical cyclone Atlantic Basin hurricanes: Indices of climatic changes. Cli- strikes along the Gulf and Atlantic coasts by merging matic Change, 42, 89–129.

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Ludlum, D. M., 1989: Early American Hurricanes 1492–1870. Lan- ——, and H. Riehl, 1981: The Hurricane and Its Impact. Louisiana caster Press, 198 pp. State University Press, 398 pp. Merrill, R. T., 1984: A comparison of large and small tropical Solow, A. R., and L. Moore, 2002: Testing for trend in North cyclones. Mon. Wea. Rev., 112, 1408–1418. Atlantic hurricane activity, 1900–98. J. Climate, 15, 3111– Muller, R. A., and G. W. Stone, 2001: A climatology of tropical 3114. Encyclo- storm and hurricane strikes to enhance vulnerability predic- Stadler, S., and T. Hughes, 2005: Wind power climatology. pedia of World Climatology, J. E. Oliver, Ed., Springer, 807–813. tion for the southeast US coast. J. Coast. Res., 17, 949–956. Unger, S., 1999: Is strange weather in the air? A study of U.S Neumann, C. J., B. R. Jarvinen, C. J. McAdie, and J. D. Elms, national network news coverage of extreme weather events. 1993: Tropical Cyclones of the North Atlantic Ocean, 1871– Climatic Change, 41, 133–150. 1992. National Climatic Data Center, 193 pp. Vermani, J. I., and R. H. Weisberg, 2006: The 2005 hurricane sea- Pielke, R. A., Jr., and R. A. Pielke Sr., 1997: Hurricanes: Their son: An echo of the past or a harbinger of the future? Geo- Nature and Impacts on Society. Wiley, 279 pp. phys. Res. Lett., 33, L16705, doi:10.1029/2006GL026869. Simpson, R. H., and M. Lawrence, 1971: Atlantic hurricane fre- Zielinski, G. A., and B. D. Keim, 2003: New England Weather, quencies along the United States Coastline. NOAA Tech. New England Climate. University Press of New England, Memo. NWS-SR-58, 14 pp. 296 pp.

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