Tropical Storm Force Research Articles

The Economic Impact of Hurricane Evacuations on a Coastal Georgia Hospital: A Case Study

Coastal hospitals are often faced with the challenging decision to either evacuate or shelter-in-place in anticipation of a hurricane predicted to make landfall. The costs associated with hospital evacuation not only include transportation of patients to inland areas, but also the loss of revenue due to interruption of regular operations and the cost of potential damage to the hospital's infrastructure. Financial data provided by Memorial Health University Medical Center (MUMC, Savannah, Georgia) such as average inpatient and outpatient revenues, personnel wages, and transportation costs, were used to estimate the potential economic impact of hurricane evacuations on a coastal hospital. The results indicate that even prior to the arrival of tropical storm force winds, the hospital will incur an estimated total expenditure of approximately $9.5 million which includes evacuation expenses and loss of revenue due to disruption of regular services. In case the hurricane makes landfall, revenue losses will continue to accumulate until the hospital is able to resume regular operations. The cost of relocating patients back to MUMC after the hurricane event and the cost of any hurricane-related damage to the hospital infrastructure must also be taken into consideration. In conclusion, even though hospital evacuation for hurricanes may be unavoidable in certain circumstances, the financial burden placed upon the hospital may be mitigated to a certain extent by forward planning, infrastructure upgrades, and the rapid resumption of regular hospital function.

Hurricane Dennis' Impact on Cuban Agriculture

Between July 7 and July 9, 2005, Hurricane Dennis moved along the southern coast of Cuba then moved across the island, enveloping nearly the entire country with strong hurricane and tropical storm force winds and driving rain. This was the fourth major hurricane to strike Cuba in the last four years. As a Category 4 storm on the Saffir-Simpson Hurricane Scale when it came ashore in central Cuba on July 8, Hurricane Dennis brought with it sustained winds reported at nearly 150 mph (240 kph) and wind gusts as high as 155 mph (250 kph), making it the strongest hurricane to strike Cuba in four decades (Havana Journal, July 10, 2005). This is EDIS document FE570, a publication of the Department of Food and Resource Economics, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL. Published August 2005.

Socioeconomic vulnerability and electric power restoration timelines in Florida: the case of Hurricane Irma

Large-scale damage to the power infrastructure from hurricanes and high-wind events can have devastating ripple effects on infrastructure, the broader economy, households, communities, and regions. Using Hurricane Irma’s impact on Florida as a case study, we examined: (1) differences in electric power outages and restoration rates between urban and rural counties; (2) the duration of electric power outages in counties exposed to tropical storm force winds versus hurricane Category 1 force winds; and (3) the relationship between the duration of power outage and socioeconomic vulnerability. We used power outage data for the period September 9, 2017–September 29, 2017. At the peak of the power outages following Hurricane Irma, over 36% of all accounts in Florida were without electricity. We found that the rural counties, predominantly served by rural electric cooperatives and municipally owned utilities, experienced longer power outages and much slower and uneven restoration times. Results of three spatial lag models show that large percentages of customers served by rural electric cooperatives and municipally owned utilities were a strong predictor of the duration of extended power outages. There was also a strong positive association across all three models between power outage duration and urban/rural county designation. Finally, there is positive spatial dependence between power outages and several social vulnerability indicators. Three socioeconomic variables found to be statistically significant highlight three different aspects of vulnerability to power outages: minority groups, population with sensory, physical and mental disability, and economic vulnerability expressed as unemployment rate. The findings from our study have broader planning and policy relevance beyond our case study area, and highlight the need for additional research to deepen our understanding of how power restoration after hurricanes contributes to and is impacted by the socioeconomic vulnerabilities of communities.

The Impact of Moist Frontogenesis and Tropopause Undulation on the Intensity, Size, and Structural Changes of Hurricane Sandy (2012)

Abstract This study examines the relative roles of moist frontogenesis and tropopause undulation in determining the intensity, size, and structural changes of Hurricane Sandy using a high-resolution cloud-resolving model. A 138-h simulation reproduces Sandy’s four distinct development stages: (i) rapid intensification, (ii) weakening, (iii) steady maximum surface wind but with large continued sea level pressure (SLP) falls, and (iv) reintensification. Results show typical correlations between intensity changes, sea surface temperature, and vertical wind shear during the first two stages. The large SLP falls during the last two stages are mostly caused by Sandy’s northward movement into lower-tropopause regions associated with an eastward-propagating midlatitude trough, where the associated lower-stratospheric warm air wraps into the storm and its surrounding areas. The steady maximum surface wind occurs because of the widespread SLP falls with weak gradients lacking significant inward advection of absolute angular momentum (AAM). Meanwhile, three spiral frontogenetic zones and associated rainbands develop internally in the outer northeastern quadrant during the last three stages when Sandy’s southeasterly warm current converges with an easterly cold current associated with an eastern Canadian high. Cyclonic inward advection of AAM along each frontal rainband accounts for the continued expansion of the tropical storm–force wind and structural changes, while deep convection in the eyewall and merging of the final two surviving frontogenetic zones generate a spiraling jet in Sandy’s northwestern quadrant, leading to its reintensification prior to landfall. The authors conclude that a series of moist frontogenesis plays a more important role than the lower-stratospheric warmth in determining Sandy’s size, intensity, and structural changes.

New York City Panel on Climate Change 2015 Report. Chapter 3: Static coastal flood mapping.

New York City Panel on Climate Change 2015 Report. Chapter 3: Static coastal flood mapping.

Optimized Tropical Cyclone Winds From QuikSCAT: A Neural Network Approach

We have developed a neural network technique for retrieving accurate 12.5-km resolution wind speeds from Ku-band scatterometer measurements in tropical cyclone conditions including typical rain events in such storms. The method was shown to retrieve accurate wind speeds up to 40 m/s when compared with aircraft reconnaissance data, including GPS dropwindsondes and Stepped-Frequency Microwave Radiometer surface wind speed measurements, and when compared to global best track maximum wind speeds. Wind directions were unchanged from the current (version 3) Jet Propulsion Laboratory (JPL) global wind vector product. The technique removes positive biases with respect to best track winds in the developing phase of tropical cyclones that occurred in the nominal (version 2) JPL QuikSCAT product. The new technique also reduces negative biases with respect to best track wind speeds that occurred in the nominal product (both versions 2 and 3) during the most extreme period of the lifetime of intense storms. The wind regime with the most notable improvement is 20–40 m/s (40–80 kn), with more modest improvement for higher winds and the improvement at lower winds comparable to that achieved previously by the version 3 JPL global rain-corrected product. The net effect of all the wind speed improvements is a much better measurement of storm intensity over time in the new product than what has been previously available. When compared with speed data from aircraft flights in Atlantic hurricanes, the new product exhibited a 1–2-m/s positive overall bias and a 3-m/s mean absolute error. The random error and systematic positive bias in the new scatterometer wind product is similar to that of the Hurricane Research Division H*WIND analyses when aircraft data are available for assimilation. This similarity may be explained by the fact that H*WIND data are used as ground truth to fit the coefficients used by the new technique to map radar measurements to wind speed. The fact that H*WIND was designed to match maximum winds while preserving radial symmetry may explain the overall positive biases that we observe in both H*WIND and the new scatterometer wind product which compared to aircraft reconnaissance data. The new scatterometer product could also be inheriting systematic biases in the presence of rain from H*WIND. Under the most extreme rain conditions, the radar signal from the surface can be lost. In such cases, the technique makes use of measurements in the 87.5-km region comprising the 7 $\times$ 7 neighboring cells around the target 12.5-km wind vector cell. In so doing, we sacrifice resolution in cases where the highest resolution region has no useful measurements. Even so, the most extreme rain conditions can result in reduced accuracy. The new technique has been used to retrieve wind fields for every tropical cyclone of tropical storm force or above that has been observed by QuikSCAT during the period of time from October 1999 to November 2009. The resulting data set has been made available online for use by the tropical cyclone research community.

FIELD INVESTIGATION OF WAVE DISSIPATION OVER SALT MARSH VEGETATION DURING TROPICAL CYCLONE

Wave data were measured along a 28 m transect using 3 pressure transducers over a 2-day period during a tropical storm. The tropical storm force winds produced waves up to 0.4 m high (zero-moment) that propagated over vegetation of Spartina alterniflora submerged under a surge of over 1 m above the marsh floor. Measured wave heights, energy losses between gages and spectral energy dissipation models of rigid vegetation were utilized to estimate wave height decay rates, integral and frequency-dependent bulk drag coefficients, and frequency distribution of energy dissipation induced by the vegetation. Measurements showed that incident waves attenuated exponentially over the vegetation. The exponential wave height decay rate decreased as Reynolds number increased. The swell was observed to decay at a slower rate than the wind sea regardless of the wave height. The linear spatial wave height reduction rate increased from 1.5% to 4% /m as incident wave height decreased. The bulk drag coefficient estimated from the field measurement decreased with increasing Reynolds and Keulegan-Carpenter numbers. The energy dissipation varied across the frequency scales with the largest magnitude observed near the spectral peaks, above which the dissipation gradually decreased. The wave energy dissipation did not linearly follow the incident energy, and the degree of non-linearity varied with the frequency. For a given spectrum, the frequency-distributed drag coefficient increased gradually up to the peak frequency and remained approximately at a stable value at the higher frequencies. This spectral variation was parameterized by introducing a frequency-dependent velocity attenuation parameter inside the canopy. The spectral drag coefficient is shown to predict the distribution of energy dissipation with more accuracy than the integral coefficients, which results in a more accurate prediction of the mean wave period and spectral width of a wave field with vegetation.

Uncertainty and Intercalibration Analysis of H*Wind

Abstract The Hurricane Research Division (HRD) Real-time Hurricane Wind Analysis System (H*Wind) is a software application used by NOAA’s HRD to create a gridded tropical cyclone wind analysis based on a wide range of observations. These analyses are used in both forecasting and research applications. Although mean bias and RMS errors are listed, H*Wind lacks robust uncertainty information that considers the contributions of random observation errors, relative biases between observation types, temporal drift resulting from combining nonsimultaneous measurements into a single analysis, and smoothing and interpolation errors introduced by the H*Wind analysis. This investigation seeks to estimate the total contributions of these sources, and thereby provide an overall uncertainty estimate for the H*Wind product. A series of statistical analyses show that in general, the total uncertainty in the H*Wind product in hurricanes is approximately 6% near the storm center, increasing to nearly 13% near the tropical storm force wind radius. The H*Wind analysis algorithm is found to introduce a positive bias to the wind speeds near the storm center, where the analyzed wind speeds are enhanced to match the highest observations. In addition, spectral analyses are performed to ensure that the filter wavelength of the final analysis product matches user specifications. With increased knowledge of bias and uncertainty sources and their effects, researchers will have a better understanding of the uncertainty in the H*Wind product and can then judge the suitability of H*Wind for various research applications.

Structure and Evolution of a Possible U.S. Landfalling Tropical Storm in 2006

Abstract A tropical disturbance made landfall near Morehead City, North Carolina, on 27 June 2006. Surface observations, Air Force reconnaissance, and Doppler velocity data suggest that the disturbance had a closed surface circulation at landfall, with maximum 1-min surface winds >18 m s−1, the threshold of tropical storm strength. A cyclostrophic wind calculation using Doppler velocity data and surface observations indicates that the circulation of the disturbance likely caused the tropical storm force winds observed, rather than an environmental pressure gradient or short-lived convective process. Doppler velocity cross sections of the disturbance further suggest that the disturbance was warm core, and an analysis of the disturbance’s environment reveals that latent heat of condensation was likely a large source of energy for the disturbance, though there was some baroclinic forcing. These observations and analyses make a compelling case for the upgrade of the disturbance to a tropical storm in the best-track database.

Synoptic- and Frontal-Scale Influences on Tropical Transition Events in the Atlantic Basin. Part II: Tropical Transition of Hurricane Karen

Abstract A finescale simulation of the tropical transition of Atlantic Hurricane Karen in October 2001 is examined to determine the processes leading to the development of upshear convection and its effects on the process of tropical transition. The analysis shows that, as in marine extratropical cyclones, the area upshear of the pretransition cyclone is characterized by reduced stability. Lower-tropospheric frontogenesis leads to an intense burst of convection there and instigates three important processes that combine to produce a full-fledged tropical cyclone. First, the convection generates intense low-level vorticity on the western half of the cyclone, which quickly dominates the cyclone’s vorticity field eventually organizing the circulation into a small-scale, intense vortex. Second, the diabatically enhanced circulation hastens the isolation of the cyclone’s developing warm core by intensifying cold air advection on the northern and western sides of the storm and by placing evaporatively cooled air into the boundary layer to the south of the cyclone. Third, upshear convection vertically redistributes potential vorticity (PV) from the tropopause to the surface and introduces a component to the upper-level winds, which advects strong, shear-inducing PV gradients away from the column above the cyclone. These three processes transform the initial extratropical cyclone into a frontless vortex with tropical storm–force winds and a warm core in a low-shear environment. These features are sufficient, given a warm enough ocean surface, to allow self-amplification of the storm as a tropical cyclone. The results further blur the distinction between tropical and extratropical cyclones as many of the processes identified as important to transition are similar to those that characterize ordinary marine cyclones and the extratropical occlusion process with the key distinctions being that here the convection is stronger and the initial upper-level feature is weaker. Thus, tropical transition of strong extratropical precursors follows the canonical midlatitude cyclone life cycle with upshear convection serving as the catalyst that both induces and organizes processes that favor tropical cyclogenesis in the postmature phase.

Tropical Cyclone Destructive Potential by Integrated Kinetic Energy

Tropical cyclone damage potential, as currently defined by the Saffir-Simpson scale and the maximum sustained surface wind speed in the storm, fails to consider the area impact of winds likely to force surge and waves or cause particular levels of damage. Integrated kinetic energy represents a framework that captures the physical process of ocean surface stress forcing waves and surge while also taking into account structural wind loading and the spatial coverage of the wind. Integrated kinetic energy was computed from gridded, objectively analyzed surface wind fields of 23 hurricanes representing large and small storms. A wind destructive potential rating was constructed by weighting wind speed threshold contributions to the integrated kinetic energy, based on observed damage in Hurricanes Andrew, Hugo, and Opal. A combined storm surge and wave destructive potential rating was assigned according to the integrated kinetic energy contributed by winds greater than tropical storm force. The ratings are based on the familiar 1–5 range, with continuous fits to allow for storms as weak as 0.1 or as strong as 5.99.

Comparison of observed gale radius statistics

Forecasts of tropical cyclone track and intensity have long been used to characterize the evolution and expected threat from a tropical storm. However, in recent years, recognition of the contributions of subtropical cyclogenesis to tropical storm formation and the process of extratropical transition to latter stages of the once-tropical storm’s lifecycle have raised awareness about the importance of storm structure. Indeed, the structure of a cyclone determines the distribution and intensity of the significant weather associated with that storm. In this study, storm structure is characterized in terms of significant wind radii. The radii of tropical storm, damaging, and hurricane-force winds, as well as the radius of maximum winds are all analyzed. These wind radii are objectively derived from the H*Wind surface wind analysis system. Initially, six years of these data are examined for consistency with previous studies. Having ascertained that the H*Wind radii are realistic, detailed comparisons are performed between the H*Wind and NHC Best Track wind radii for two years (2004 and 2005) of North Atlantic tropical storm and hurricane cases. This intercomparison reveals an unexpected bias: the H*Wind radii are consistently larger than the NHC Best Track for all but the smallest and least intense storms. Further examination of the objectively-determined H*Wind tropical storm force wind radius data compared to subjectively-determined radii for the same storm times demonstrates that the objective wind radii are underestimating the extent of the tropical storm force wind area. Since the objective H*Wind radii are large compared to the NHC Best Track – and yet underestimate the area of tropical storm force winds – this argues for further examination of the methods used to ascertain these significant wind radii.

Sediment transport on the mid-continental shelf in Onslow Bay, North Carolina during Hurricane Isabel

Hurricane Isabel made landfall on the southeastern U.S. coast along the lower Outer Banks of North Carolina near Cape Lookout, NC on September 18, 2003. An instrumented quadrapod frame moored approximately 43.5 km off the coast of Wilmington, NC in Onslow Bay, at a depth of approximately 30 m, was present on the shelf when the hurricane passed approximately 160 km from Onslow Bay. The attached instrumentation includes a downward-looking Pulse-Coherent Acoustic Doppler Profiler (PC-ADP) and an upward-looking Acoustic Doppler Current Profiler (ADCP). Simultaneous measurements of flow velocities from the surface to the seabed along with acoustic backscatter measurements and seabed elevation were obtained during this storm event. Three days prior to the direct effects of the hurricane, long-period swells (14–17 s) began to impact the area causing sediment transport to occur on the mid-shelf. Shear velocities calculated from a bottom boundary layer model ranged from approximately 6 to 10 cm s −1 over the course of the sediment transport event. Based on shear velocity calculations, bedload and suspended sediment transport were occurring at the site 72 h prior to the passage of the hurricane as long-period swells reached heights of 4 m. The seabed altimeter recorded large fluctuations during the storm but was unable to trace elevation changes due to the presence of a highly concentrated layer of suspended sediments in the lower 10 cm of the bottom boundary layer. Large amounts of suspended sediment transport occurred in the along-shelf direction towards the southwest after tropical storm force winds of 30 m s −1 began to directly affect the area and wind-driven currents were generated. Wind-driven, subtidal currents responded rapidly to local wind forcing and shifted from 15 cm s −1 towards the southwest to 16 cm s −1 towards the northeast. Model calculated velocity profiles compared well with measured current velocity profiles. Boxcores collected pre- and post-storm show a storm layer of approximately 5 cm and a sediment trap that was attached to the frame 30 cm above the bed collected approximately 400 cm 3 of fine to medium sands that were suspended during the storm.

A Reanalysis of the Surface Winds for Hurricane Donna of 1960

Hurricane Donna, the only major hurricane to strike the United States during the 1960 Atlantic hurricane season, passed over the middle Florida Keys near Sombrero Key before making landfall southeast of Naples, near Goodland, Florida, on 10 September at approximately 1600 UTC. This study makes detailed retrospective surface wind analyses of Hurricane Donna utilizing the National Oceanic and Atmospheric Administration (NOAA) Hurricane Research Division's (HRD) H*Wind surface wind analysis system. Analyses were produced at intervals of 6 h between 1800 UTC 9 September and 1200 UTC 11 September 1960 while the hurricane was close to and over Florida. These analyses depict the storm track as well as the distribution and extent of tropical storm force, 50 kt (25.7 m s−1), and the hurricane-force wind radii throughout this time period and include new methodologies for adjusting aircraft flight-level data to the surface in the tropical cyclone core environment. Algorithms were developed to account for the effects of eyewall tilt and the warm core structure typical of tropical cyclones. Additional methods were developed using global positioning system (GPS) dropwindsondes (sondes) to more accurately adjust boundary layer winds to equivalent surface winds. The Kaplan–DeMaria Inland Wind Decay Model was also used for the first time to adjust landfall data being input into the H*Wind system. These data were used to generate low-weighted background fields that helped generate postlandfall wind field analyses of Hurricane Donna. Finally, swaths of peak winds, duration of hurricane- and major hurricane–force winds, and wind steadiness were produced to facilitate damage assessment. The information provided by these objective analyses is significantly more detailed than the more limited descriptions of peak winds, storm position, and minimum central pressure available in the National Hurricane Center's (NHC) hurricane database archive (HURDAT).