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Airborne bathymetric lidar surveys taken in Florida before and after the severe 2004 and 2005 hurricane seasons show infilling of seventeen dredged nearshore borrow pits. During these seasons, groups of pits captured volumes that were the equivalent of up to four years of net longshore transport, even though only one of the seventeen pits studied was inside the presumed depth of closure. Unsurprisingly, dimensionless infilling increased strongly with the ratio of wave height to pit depth. For open coast pits with large alongshore lengths, cross-shore infilling appeared to dominate over longshore infilling but both processes may be of comparable importance in shorter pits. Infilling of three borrow pits adjacent to ebb shoals was found to be considerably larger than on open coasts. Bathymetric changes in borrow pits occurred at greater depths than on nearby undisturbed profiles. Crude estimates of the long term infilling rates from tropical cyclones indicate that annual infilling volumes may be equivalent to more than one quarter of the expected net longshore transport at some locations. However, the episodic nature of hurricanes means that infilling events will be highly irregular. CE Database subject headings: Coastal engineering; Sediment transport; Water waves; Hurricanes; Florida. Author keywords: Coastal engineering; Sediment transport; Water waves; Hurricanes. DOI: 10.1061/(ASCE)WW.1943-5460.0000024

Analyses of tropical cyclones created in an idealized environment reveal how and why cloud microphysical assumptions can influence storm motion, including speed and direction. It is well known that in the absence of a mean flow, a leading factor in storm propagation is the establishment of 'beta gyres' owing to planetary vorticity advection by the storm's circulation. Previous research demonstrated that tangential winds well beyond the core influence storm motion by helping to determine the gyres' orientation and intensity. Microphysical assumptions, especially involving average particle fall speeds, can strongly influence the winds at outer radius. More specifically, microphysics modulates the radial distribution of column-average virtual temperature, which largely determines the radial surface pressure gradient and therefore the winds because they tend to be in gradient balance beyond the core. Microphysics schemes can differ markedly with respect to average fall speed, depending on the complexity of the scheme and how interactions among condensation types are handled. Average fall speed controls the outward movement of particles produced in the eyewall into the anvil, where they can influence the environment through cloud-radiative interactions and phase changes. With the assistance of some special sensitivity tests, the influence of microphysics and fall speed on radial temperature gradients, leading to different outer wind strengths and tracks, is shown. Among other things. this work demonstrates that the treatment of outer rainbands in operational models can potentially influence how simulated storms move, thus affecting position forecasts.

In hurricane eyewalls, the vertical stretching effect tends to produce an annular ring of high vorticity. Idealized, unforced nondivergent barotropic model results have suggested such rings of vorticity are often barotropically unstable, leading to strong asymmetric mixing events where vorticity is mixed inward into a more stable configuration. Such mixing events most often result in weakened maximum winds. The manner in which forcing modifies these unforced simulations remains an open question. In the current study, a forced, two-dimensional barotropic model is used to systematically study the sensitivity of vorticity rings to ring geometry and spatially and temporally varying forcing. The simulations reveal an internal mechanism that interrupts the intensification process resulting from vorficity generation in the hurricane eyewall. This internal control mechanism is due to vorticity mixing in the region of the eye and eyewall and can manifest itself in two antithetical forms--as a transient 'intensification brake' during symmetric intensification or as an enhancer of intensification through efficient transport of vorticity from the eyewall, where it is generated, to the eye.

The transport and mixing characteristics of a large sample of air parcels within a mature and vertically sheared hurricane vortex are examined. Data from a high-resolution (2-km horizontal grid spacing) numerical simulation of real-case Hurricane Bonnie (1998) are used to calculate Lagrangian trajectories of air parcels in various subdomains of the hurricane (namely, the eye, eyewall, and near environment) to study the degree of interaction (transport and mixing) between these subdomains. It is found that 1) there is transport and mixing from the low-level eye to the eyewall that carries air possessing relatively high values of equivalent potential temperature ([[theta].sub.e]), which can enhance the efficiency of the hurricane heat engine; 2) a portion of the low-level inflow of the hurricane bypasses the eyewall to enter the eye, and this air both replaces the mass of the low-level eye and lingers for a sufficient time (order 1 h) to acquire enhanced entropy characteristics through interaction with the ocean beneath the eye; 3) air in the mid- to upper-level eye is exchanged with the eyewall such that more than half the air of the eye is exchanged in 5 h in this case of a sheared hurricane; and 4) that one-fifth of the mass in the eyewall at a height of 5 km has an origin in the mid- to upper-level environment where [[theta].sub.e] is much less than in the eyewall, which ventilates the ensemble average eyewall [[theta].sub.e] by about 1 K. Implications of these findings for the problem of hurricane intensity forecasting are briefly discussed.

The Hurricane Rainband and Intensity Change Experiment (RAINEX) used three P3 aircraft aided by high-resolution numerical modeling and satellite communications to investigate the 2005 Hurricanes Katrina, Ophelia, and Rita. The aim was to increase the understanding of tropical cyclone intensity change by interactions between a tropical cyclone's inner core and rainbands. All three aircraft had dual-Doppler radars, with the Electra Doppler Radar (ELDORA) on board the Naval Research Laboratory's P3 aircraft, providing particularly detailed Doppler radar data. Numerical model forecasts helped plan the aircraft missions, and innovative communications and data transfer in real time allowed the flights to be coordinated from a ground-based operations center. The P3 aircraft released approximately 600 dropsondes in locations targeted for optimal coordination with the Doppler radar data, as guided by the operations center. The storms were observed in all stages of development, from tropical depression to category 5 hurricane. The data from RAINEX are readily available through an online Field Catalog and RAINEX Data Archive. The RAINEX data-set is illustrated in this article by a preliminary analysis of Hurricane Rita, which was documented by multiaircraft flights on five days 1) while a tropical storm, 2) while rapidly intensifying to a category 5 hurricane, 3) during an eye-wall replacement, 4) when the hurricane became asymmetric upon encountering environmental shear, and 5) iust prior to landfall.

An unprecedented dataset of category-5 Hurricane Isabel was collected on 12-14 September 2003. This two-part series focuses on novel dynamical and thermodynamical aspects of Isabel's innercore structure on 13 September. In Part I, using a composite of dropwindsonde and in situ aircraft data, the authors suggested that the axisymmetric structure of Isabel showed that the storm was superintense. Mesocyclones seen clearly in satellite imagery within the eye of Hurricane Isabel are hypothesized to mix high-entropy air at low levels in the eye into the eyewall, stimulating explosive convective development and a concomitant local horizontal wind acceleration. Part II focuses on a unique set of observations into an extraordinary small- (miso) scale cyclonic feature inside of the inner edge of the eyewall of Hurricane Isabel. A dropwindsonde released into this feature measured the strongest known horizontal wind in a tropical cyclone. This particular observation is discussed in the context of concurrent observations from airborne Doppler radar and other airborne instruments. These observations show wind even stronger than the system-scale superintense wind suggested in Part I. Speculation on the frequency of occurrence of these 'little whirls' and their potentially catastrophic impacts are presented.

This study is an observational analysis of the inner-core structure, sea surface temperature, outflow layer, and atmospheric boundary layer of an intense tropical cyclone whose intensity and structure is consistent with recent numerical and theoretical predictions of superintense storms. The findings suggest new scientific challenges for the current understanding of hurricanes. Unprecedented observations of the category-5 Hurricane Isabel (2003) were collected during 12-14 September. This two-part article reports novel dynamic and thermodynamic aspects of the inner-core structure of Isabel on 13 September that were made possible by analysis of these data. Here, a composite of the axisymmetric structure of the inner core and environment of Isabel is estimated using global positioning system dropwindsondes and in situ aircraft data. In Part II, an extreme wind speed observation on the same day is discussed in the context of this work. The axisymmetric data composite suggests a reservoir of high-entropy air inside the low-level eye and significant penetration of inflowing near-surface air from outside. The analysis suggests that the low-level air penetrating the eye is enhanced thermodynamically by acquiring additional entropy through interaction with the ocean and replaces air mixed out of the eye. The results support the hypothesis that this high-entropy eye air 'turboboosts' the hurricane engine upon its injection into the eyewall clouds. Recent estimates of the ratio of sea-to-air enthalpy and momentum exchange at high wind speeds are used to suggest that Isabel utilized this extra power to exceed the previously assumed intensity upper bound by 10-35 m [s.sup.1] for the given environmental conditions. Additional study with other datasets is encouraged to further test the super-intensity hypothesis.

This paper reviews recent research on tropical cyclones and climate change from the perspective of event risk--the physical behavior of storms; vulnerability--the characteristics of a system that create the potential for impacts, but are independent of event risk; and also outcome risk--the integration of considerations of vulnerability with event risk to characterize an event that causes losses. The paper concludes that with no trend identified in various metrics of hurricane damage over the twentieth century, it is exceedingly unlikely that scientists will identify large changes in historical storm behavior that have significant societal implications, though scientists may identify discernible changes in storm behavior. Looking to the future, until scientists conclude a) that there will be changes to storms that are significantly larger than observed in the past, b) that such changes are correlated to measures of societal impact, and c) that the effects of such changes are significant in the context of inexorable growth in population and property at risk, then it is reasonable to conclude that the significance of any connection of human-caused climate change to hurricane impacts necessarily has been and will continue to be exceedingly small.