Spatial and Temporal Characteristics of Tornado Path Direction*

Common perception is that tornadoes travel in paths from the southwest quadrant of directions toward the northeast. This study examines path directions for 6,194 tornadoes that occurred in the eastern two‐thirds of the United States during the twenty‐three‐year period 1980–2002. At the national scale, nearly 70 percent of tornadoes included in the study propagated from the west, west‐southwest, and southwest, with west‐southwest being the highest frequency origin direction. Nevertheless, distinct seasonal and regional variations were found. In central and northern areas of the country, a more westerly or northwesterly path origin prevails during late spring and summer. The midtropospheric flow, convective typology, and synoptic patterns of tornado outbreaks are thought to contribute to the distributions observed in the climatology.     

Vulnerability to Hurricane Damage on the U.S. Gulf Coast Since 1950

We study hurricane risk on the U.S. Gulf Coast during 1950‐2005, estimating the wind damage and storm surge from every hurricane in this extended period. Wind damage is estimated from the known path and wind speeds of individual storms and calibrated to fit actual damage reports for a sample of Gulf Coast storms. Storm surge is estimated using the SLOSH model developed by NOAA. These models provide the first comprehensive overview of the hurricane storm hazard as it has been experienced over a fifty‐six‐year period. We link the estimated damage with information on the population and specific socio‐demographic components of the population (by age, race, and poverty status). Results show that white, young adult, and nonpoor populations have shifted over time away from zones with higher risk of wind damage, while more vulnerable population groups–the elderly, African Americans, and poor—have moved in the opposite direction. All groups have moved away from areas with high risk of storm surge since 1970. But in this case, perhaps because living near the water is still perceived as an amenity, those at highest risk are whites, elderly, and nonpoor households. Here exposure represents a trade‐off between the risk and the amenity.     

Hurricane 07B in the Godavari Delta, Andhra Pradesh, India: vulnerability, mitigation and the spatial impact

Few hurricane impact studies provide robust spatial parameters of damage or relate geographical patterns of destruction accurately to storm trajectories or agencies. A detailed spatial analysis is, therefore, presented of the destruction caused by tropical hurricane 07B which made landfall on 6/7 November 1996 over the Godavari Delta region, Andhra Pradesh, eastern India. Patterns of destruction by storm surge, wind and flood water are quantitatively mapped for death tolls, house destruction and agricultural damage using local administrative ( mandal ) data bases. Results show that most impact occurred near the coast, but a well-defined path of destruction across the central part of the delta can be identified. Such mapping studies fail to indicate the types of individuals and social groups most affected by the storm hazard and their response to it. An investigation of landowning farmers, female migrant rural labourers and fishing communities in the delta shows that poverty and social ordering in Indian society puts differential limits on the risk reduction abilities of individuals and social groups in the face of the cyclone hazard. The paper also demonstrates that 'top down' institutional measures to reduce the effects of storm damage such as those introduced in the aftermath of hurricane 07B, including early storm warning and evacuation procedures and rehabilitation programmes, remain largely ineffective. It is suggested that the introduction of more 'bottom up' community-based programmes which seek to improve the risk awareness and risk avoiding abilities of affected individuals and groups would be much more beneficial. The case material on hurricane 07B and its effects are placed in context by reviewing and updating long and medium-term time series records of storm frequencies and impacts in the Bay of Bengal and particularly along the eastern coastline of India.     

新奥尔良飓风灾难与华南沿海台风暴潮

分析了新奥尔良的地理环境,概述了卡特里娜飓风与丽塔飓风及其对新奥尔良的影响.简述了华南沿海的台风暴潮灾害情况,提出了新奥尔良飓风灾难对华南沿海的几点警示:(1)加强提高防御台风暴潮灾害的认识;(2)保护好沿海抗御台风暴潮的"前沿阵地;(3)加强和完善防台风暴潮应急预案;(4)应对台风暴潮要充分考虑全球环境变化.     

Cloud-to-ground lightning signatures of long-lived tornadic supercells on 27–28 April 2011

This study integrates past research methodologies, data from the National Lightning Detection Network (NLDN), and geographic information system techniques to assess the lightning and severe weather hazard relationship for the 27–28 April 2011 United States tornado outbreak. NLDN and Doppler radar data are used to examine the cloud-to-ground (CG) lightning characteristics associated with seven supercell thunderstorms that produced long-track, significant and/or violent tornadoes. Analyses indicate that CG lightning flashes alone do not provide enough information for the detection of a lightning jump prior to tornadogenesis. All seven supercells were dominated by negative-polarity CG lightning flashes; which is expected due to the geographic location and elevated low-level moisture found in the outbreak environment. The correlation between low-level mesocyclone strength and total CG lightning flash rate was varied and inconsistent among all storms despite their formation and sustenance in similar environmental and geographic space. Additional case studies, as well as climatological approaches, are required to discover if the varying lightning–tornado relationships found in this study are consistent with other tornadic environments.     

Tropical Storm Gamma and the Mosquitia of eastern Honduras: a little-known story from the 2005 hurricane season

The 2005 Atlantic hurricane season was unprecedented in terms of storm activity in the United States, Mexico, Central America and Caribbean. Given the impacts of hurricanes Katrina and Rita, the Honduran Mosquitia sparked little attention despite being hit by two hurricanes and a tropical storm in 2005. This article recounts the history of these storms in the Afro-Caribbean community of Batalla, drawing from public weather advisories and testimony of local residents obtained through participatory research. We contextualise this local history with results from the first paleotempestological study undertaken in the Mosquitia to shed light on long-term risk of catastrophic storms in the region and to demonstrate the value of integrating these two research approaches. Our findings contribute to recent ethnographic research on hazards by describing how a coastal people understand and respond to tropical cyclones and how landscape change influences the vulnerability of a coastal area. Although residents have not witnessed a storm as intense as those documented in the paleotempestological record, their knowledge and perceptions show how tropical cyclones can be disasters while leaving behind no sedimentary records. The paleotempestological evidence, however, reminds us that catastrophic hurricanes have struck the Mosquitia in the past and will do so again in the future. Understanding the interactions between contemporary human perceptions and responses and long-term hurricane risk provides insight for emergency managers and local stakeholders to better prepare for such a catastrophic event.     

THE DIURANAL DISTRIBUTION OF LARGE HAIL OVER THE UNITED STATES

The diurnal course of large hail varies over the United States. The time of maximum of large hail changes from near 1500 hours on the east coast to between 1800 and 1900 hours on the Great Plains. The north-to-south differences are smaller except near the Gulf Coast, where secondary maxima occur. In some areas the time of maximum of large hail differs from the maxima times of tornadoes, heavy rain, and thunderstorms.     

THE DIURANAL DISTRIBUTION OF LARGE HAIL OVER THE UNITED STATES

The diurnal course of large hail varies over the United States. The time of maximum of large hail changes from near 1500 hours on the east coast to between 1800 and 1900 hours on the Great Plains. The north-to-south differences are smaller except near the Gulf Coast, where secondary maxima occur. In some areas the time of maximum of large hail differs from the maxima times of tornadoes, heavy rain, and thunderstorms.     

Factors controlling the survival of coastal dunes during multiple hurricane impacts in 2004 and 2005: Santa Rosa barrier island, Florida

Santa Rosa Island is an 85 km-long, wave-dominated low-lying barrier island situated along the northwestern Florida coast, facing the Gulf of Mexico. The entire island was severely impacted by Ivan, a strong category 3 hurricane that made landfall about 45 km to the west in September of 2004. Ten months later in July of 2005, Dennis, another category 3 hurricane, made landfall about 30 km east of the western tip of the island. Santa Rosa Island is characterized by well-developed but relatively low dunefields, described in this paper as incipient and established dunes, based on the presence of grassy and woody types of vegetation, respectively. The dunes were severely eroded by the two hurricanes. This paper investigates the factors controlling the regional-scale destruction and survival of the dunefields.Dune survival is controlled by: 1) hurricane characteristics, including intensity, duration, and frequency, and 2) morphological parameters including width of the barrier island, height and width of the dunefields, vegetation type, distance of the dunes to the ocean, and continuity of the dunefields. Three processes of dune destruction are described including, from most to least severe, inundation, overwash, and scarping. The interaction of all the above factors determines the different dune responses to the storm impacts. In general, the extensive and densely woody vegetated dunefields near the bay-side shoreline survived the storms, while the discontinuous dunes with grassy vegetation near the Gulf shoreline were almost completely destroyed.     

A SYNOPTIC CLIMATOLOGY OF NORTHEASTERN UNITED STATES TORNADOES

This study documents the spatial and temporal characteristics of northeast United States tornadoes and the synoptic patterns associated with their development. Daily 1200 UTC surface pressure, 500 mb height and 850 mb temperature data are used in a compositing analysis to indicate the general conditions on tornado-producing days during four quasi-seasonal periods. Temporally, two-thirds of all northeast tornadoes occur between the hours of 1800 UTC and 0000 UTC. Annually, greater than 75% occur during the four-month period from May through August. During the period of study (1950 through 1986) the region had an average of 30 tornado occurrences per year. Spatially, three preferred areas of tornadic development are identified across the northeast region. These areas include western and southeastern Pennsylvania and north-central Massachusetts. The general synoptic patterns associated with tornadic events in the northeast United States remain consistent throughout the year. The composite analyses indicate that the presence of a strong surface low pressure system moving through the Great Lakes, coupled with significant upper-level divergence associated with a vigorous shortwave feature and a cold frontal boundary, are the synoptic features most common during the initiation of tornadic storms in this region. [Key words: synoptic climatology, tornadoes, northeastern United States.]     

A climatological study of the effect of sea-surface temperature on North Atlantic hurricane intensification

The climatic influence of sea-surface temperature (SST) on intensification is examined for North Atlantic hurricanes by averaging hourly intensity increases from best-track data over the period 1986–2013 in 4° by 4° latitude–longitude grid cells. Independent monthly SST data over the same period are averaged in the same cells. After removing cells with cold water or fast moving hurricanes, the SST effect on intensification, at the climate scale, is quantified by regressing intensification onto SST while controlling for average intensity. The regression is performed using a generalized linear model from a gamma family and a logarithmic link function. The model shows a statistically significant relationship, with higher intensification values associated with higher SST values. On average, mean intensification increases by 16% [(9,?20)% uncertainty interval] for every 1 °C increase in mean SST. A clustered region where the model underpredicts intensification is noted over the southeastern Caribbean Sea, perhaps related to the fresh water plume from the Orinoco River.     

Households’ Resilience to Hurricanes in Coastal Communities of Oaxaca,Mexico

Hurricanes represent a common threat to coastal communities, affecting livelihood strategies and assets. Households are resilient if they can recover from a stress or shock while maintaining and arranging assets to secure a sustainable livelihood. The objective of this research is to measure the degree of resilience in the coastal households of Oaxaca, Mexico, following a hurricane using the asset approach and describing diversity, connectivity, and slow variables. The results show different degrees of resilience among the households and that social, natural, and financial capital are relevant to resilience. The diversification of income, savings, community help, natural resource use, and government transfers is among the most important assets. In particular, social capital and natural capital determine the structure and dynamics of the system.     

Patterns and Controls of Hurricane-Caused Forest Damage: A Landscape-Scale Analysis of Treefall Direction Following Hurricane Katrina∗

To clarify broad-scale patterns and controls of treefall directionality from Hurricane Katrina, we examined fall directions across a 4,500 km² landscape mosaic in southern Mississippi using georeferenced, planar-rectified aerial photographs. Analyses using directional statistics, measures of local spatial autocorrelation, and general linear modeling indicated that treefall was significantly directional for nearly all of our locations and constrained primarily by mesoscale surface wind directions and landscape setting. None of our plots exhibited fall angles consistent with damage caused by wind reversals following the passage of the storm or by microbursts or tornadoes spawned by the hurricane. When coupled with results from other studies focused on hurricane-caused damage, these results suggest that it is possible to develop empirical, landscape-scale models of wind impacts or stand vulnerability using basic site information (e.g., topography, soils), biotic conditions (e.g., land cover, forest attributes), and generalized, but readily available, estimates of surface wind flow patterns.     

THE SPATIAL DISTRIBUTION OF INFLATION: A PUZZLE FOR ECONOMIC GEOGRAPHERS

Interviewers presented 400 residents of Pinellas County, Florida, with sets of hypothetical hurricane threats to assess the effect of hurricane probability forecasts and other risk indicators on public response to the threats. Evacuation notices from local officials were more important than other threat variables, and hurricane probabilities did little to modify that effect. Respondents appeared to comprehend and use the probability information reasonably. Evacuation behavior in actual hurricane threats is consistent with the survey findings.     

Public Response to Hurricane Probability Forecasts

Interviewers presented 400 residents of Pinellas County, Florida, with sets of hypothetical hurricane threats to assess the effect of hurricane probability forecasts and other risk indicators on public response to the threats. Evacuation notices from local officials were more important than other threat variables, and hurricane probabilities did little to modify that effect. Respondents appeared to comprehend and use the probability information reasonably. Evacuation behavior in actual hurricane threats is consistent with the survey findings.     

An analysis of intra-event precipitation variability for the United States (1980–2010)

Hourly precipitation data were collected from 143 first-order US weather stations during the period from 1980 to 2009 to assess the internal distribution of precipitation events lasting at least three hours. A total of 46,595 individual precipitation events were identified and evaluated using the mean, standard deviation, skewness, kurtosis, and the number of peaks occurring within an event. Mean event duration is longest along the West and Northwest coasts, the Mid-South, the Mid-Atlantic, and the Northeast; while shorter-duration events are more frequent in the Rocky Mountains, the Southwest, and the Great Plains. Mean event precipitation and standard deviation are greatest along the Gulf Coast and decrease inland. Precipitation events are positively skewed, indicating that more precipitation tends to occur earlier in the event. The most positively-skewed events are also located in regions flanking the Gulf of Mexico, while less-skewed events are common in the Northwest and Rocky Mountain regions. Event kurtosis is negative throughout the entire USA, with the highest negative values generally west of the Front Range, where cyclonic development and transition produce more evenly distributed precipitation within storms. Intra-event precipitation maxima were also evaluated, with western Florida and the desert Southwest having the greatest number per event.     

Linking hurricane landfalls,precipitation variability,fires, and vegetation response over the past millennium from analysis of coastal lagoon sediments,southwestern Dominican Republic

We reconstructed the late-Holocene environmental history of a coastal lagoon in semi-arid southwestern Hispaniola through multiproxy analysis of a sediment core, including pollen, macroscopic and microscopic charcoal, loss-on-ignition analysis (LOI), stable isotope analysis, bulk density, and magnetic susceptibility. Four chronological accelerator mass spectrometry radiocarbon dates indicated that our core represents the past ~1000 years. We interpreted ten hurricanes events over the past millennium from high-resolution geological proxies, LOI data, and ostracod valve stable oxygen isotope data, thus producing the first long record of hurricanes from the Dominican Republic. Geological proxies indicated a high-energy event abruptly changed the ecosystem state of our core site from a shallow mangrove wetland to a lacustrine environment ~330 cal yr BP. We interpret the driver of that event to be the landfall of a strong hurricane that initiated lowland flooding, mangrove mortality, and subsequent peat collapse at the core site. Pollen data indicated that during the relatively moist Medieval Warm Period (MWP), hurricanes led to temporary declines in tropical dry forest taxa that recovered within several decades following disturbance. By comparison, during the relatively arid Little Ice Age (LIA), when precipitation was highly variable in the circum-Caribbean, closely spaced hurricanes seemed to delay forest recovery. Sedimentary charcoal concentrations revealed increased fire activity after inferred hurricane landfalls in the MWP, providing evidence of a link between enhanced biomass and fuel availability during moister periods and burning in recently disturbed dry forests and scrub of our semi-arid study region. Our interpretations of increased aridity and precipitation variability, indicated by alternating thin layers of microbial mats with evaporite layers, along with more frequent hurricanes from ~330 cal yr BP to present, generally agree with other sedimentary records from the circum-Caribbean, and may be linked to a more southerly position of the Intertropical Convergence Zone during the LIA.     

Post‐Katrina Population Loss and Uneven Recovery in New Orleans, 2000–2010

New Orleans has suffered from a significant population decline during 2000–2010, mainly due to Hurricane Katrina in 2005. Regression models are used here to explain the spatial variability of population change in New Orleans by variables such as proximity (distance or travel time) to the central business district (CBD), a natural environment variable “elevation”, and two composite socio‐demographic indices derived from variables in the census. The research reveals a U‐shaped population‐change profile with distance or travel time from the CBD, population loss bottomed at 4–5 kilometers (10–15 minutes) from the CBD and recovered towards both the CBD and suburbs. This suggests possible converging forces of suburbanization (that is, a nationwide trend that began long before the hurricane) and the CBD's anchoring role in the post‐Katrina recovery. Greater population loss was also observed in the socioeconomically disadvantaged and lower‐elevated areas, but neighborhoods of Hispanic concentration experienced less population loss.     

Geologic and societal factors affecting the international oceanic transport of aggregate

Crushed stone and sand and gravel are the two main sources of natural aggregate, and together comprise approximately half the volume and tonnage of mined material in the United States. Natural aggregate is a bulky, heavy material without special or unique properties, and it is commonly used near its source of production to minimize haulage cost. However, remoteness is no longer an absolute disqualifier for the production of aggregate. Today interstate aggregate routinely is shipped hundreds of kilometers by rail and barge. In addition, during 1992, the United States imported 1,317,000 metric tons of aggregate from Canada and 1,531,000 metric tons from Mexico. A number of ports on the Atlantic Coast and Gulf Coast of the United States receive imports of crushed stone from foreign sources for transport to various parts of the eastern United States. These areas either lack adequate supplies of aggregate or are augmenting their supplies because they have difficulties meeting current demand. These difficulties may include poor stone quality, environmental permitting problems, or transportation. Certain societal and geologic conditions of New York City and Philadelphia along the Atlantic Coast, and Tampa and New Orleans along the Gulf Coast, are discussed to demonstrate the different combinations of issues that contribute to the economic viability of importing crushed stone.     

The spatial distribution of tornadoes and high wind impacts associated with inland-moving tropical cyclones in the southeastern United States

The southeastern United States is routinely hit by tropical cyclones (TC). As TC track inland and dissipate their inland impacts can be substantial. This study examined the spatial patterns of societal impacts associated with tornadoes and high winds with 31 inland-moving TC that made landfall from 1985 to 2008. Hourly weather information was collected from all available first-order weather stations affected by each storm, as well as tropical cyclone preliminary reports issued from the National Hurricane Center. Societal impacts were identified through selected newspapers across the region and the National Climatic Data Center’s Storm Data. Geographic Information System (GIS) software was employed to make geometric measurements of the distance and direction of the impacts relative to storm center. From these measurements, the spatial distribution of the societal and meteorological impacts was plotted relative to the track (e.g., left vs. right) and location (forward vs. rear sector) of the cyclone center. Various tropical cyclone attributes, including size, strength, and forward speed of movement were then related to the occurrence of different impacts and their location relative to the cyclone track. The majority of tropical cyclone tornado and high wind impacts occur in the right-forward sector of the tropical cyclone. However, many TC produce impacts that occur in other sectors far from the center of circulation. These abnormalities are associated in many cases with interactions between the tropical cyclone circulation, topography, peripheral dry air, and extratropical synoptic weather features.