Hurricane Size Research Articles

The Impacts of Adjusting Momentum Roughness Length on Strong and Weak Hurricane Forecasts: A Comprehensive Analysis of Weather Simulations and Observations

Abstract The momentum roughness length (z0) significantly impacts wind predictions in weather and climate models. Nevertheless, the impacts of z0 parameterizations in different wind regimes and various model configurations on the hurricane size, intensity, and track simulations have not been thoroughly established. To bridge this knowledge gap, a comprehensive analysis of 310 simulations of 10 real hurricanes using the Weather Research and Forecasting (WRF) Model is conducted in comparison with observations. Our results show that the default z0 parameterizations in WRF perform well for weak (category 1–2) hurricanes; however, they underestimate the intensities of strong (category 3–5) hurricanes. This finding is independent of model resolution or boundary layer schemes. The default values of z0 in WRF agree with the observational estimates from dropsonde data in weak hurricanes while they are much larger than observations in strong hurricanes regime. Decreasing z0 close to the values of observational estimates and theoretical hurricane intensity models in high wind regimes (≳45 m s−1) led to significant improvements in the intensity forecasts of strong hurricanes. A momentum budget analysis dynamically explained why the reduction of z0 (decreased surface turbulent stresses) leads to stronger simulated storms.

Climate change impacts to the coastal flood hazard in the northeastern United States

It is widely accepted that climate change will cause sea level rise and increase the coastal flood hazard in many places. However, climate change also has significant implications for hurricane climatology. While the effect of climate change on hurricane frequency is inconclusive, there is a general consensus among climate scientists that hurricane intensity will increase over the coming decades. A number of studies indicate that hurricane size and translation speed may intensify with climate change as well. Each of these properties influences storm surge generation and propagation, and thus has significant implications for the coastal flood hazard, particularly in the densely populated northeast region of the U.S. As coastal populations grow, increasing the resilience of the built environment will become an increasingly necessary priority. Local, detailed, and comprehensive flood hazard assessment is a central aspect of such efforts. In this work, we integrate global climate data, statistical-deterministic hurricane modeling, physics-based numerical storm surge modeling, and extreme value analysis methods to comprehensively assess the present day and end of century flood hazard due to hurricanes for several coastal communities along the U.S. North Atlantic coastline. We find that by the end of the century, annual exceedance probabilities of the 100-year flood may increase by factors as great as 7 due to sea level rise, and on average projected changes to tropical cyclone climatology cause these probabilities to double. For truly effective long-term resilience efforts, coastal engineers, planners, and other stakeholders must account for climate change impacts to both sea level and tropical storm climatology.

Effects of hurricane forward speed and approach angle on storm surges: an idealized numerical experiment

The effects of hurricane forward speed (V) and approach angle (θ) on storm surge are important and a systematic investigation covering possible and continuous ranges of these parameters has not been done before. Here we present such a study with a numerical experiment using the Finite Volume Community Ocean Model (FVCOM). The hurricane track is simplified as a straight line, such that V and θ fully define the motion of the hurricane. The maximum surge is contributed by both free waves and a forced storm surge wave moving with the hurricane. Among the free waves, Kelvin-type waves can only propagate in the down-coast direction. Simulations show that those waves can only have a significant positive storm surge when the hurricane velocity has a down-coast component. The optimal values of V and θ that maximize the storm surge in an idealized semi-circular ocean basin are functions of the bathymetry. For a constant bathymetry, the maximum surge occurs when the hurricane approaches the coast from the normal direction when the free wave generation is minimal; for a stepped bathymetry, the maximum surge occurs at a certain acute approach angle which maximizes the duration of persistent wind forcing; a step-like bathymetry with a sloped shelf is similar to the stepped bathymetry, with the added possibility of landfall resonance when the free and forced waves are moving at about the same velocity. For other cases, the storm surge is smaller, given other parameters (hurricane size, maximum wind speed, etc.) unchanged.

Hurricane wind hazard assessment for a rapidly warming climate scenario

Although there is still much debate as to the causes, it is generally accepted in the scientific community that the climate is changing. The IPCC (2007) Fourth Assessment Report states that warming of the climate system is unequivocal, and that this warming has likely influenced observed changes in many physical systems at the global scale. In order to meet target safety and performances levels when designing structures and infrastructure systems in the future, it is essential that current design codes and standards adapt to reflect global climate change. With the trend toward performance-based engineering, for US coastal regions, along the Atlantic Ocean and Gulf of Mexico, this means a quantitative assessment of climate change impact on hurricane hazard performance levels is needed.This study couples a projected climate change scenario with state-of-the-art probabilistic event-based simulation procedures to assess the hurricane wind hazard under a worst-case climate change scenario. The hurricane wind hazard is defined herein using the hurricane intensity (maximum wind speed) and hurricane size (radius to maximum wind speed). Through Monte Carlo simulation, 10,000 years of hurricane events, under the current (2012) and future (2100) climate conditions, were generated. The hurricane intensity distribution and the joint distribution of hurricane intensity and size, under current and future climate scenarios, were then compared.

Assessing Climate Change Impact on the U.S. East Coast Hurricane Hazard: Temperature, Frequency, and Track

This paper presents a study to assess the impact of possible future climate change on the hurricane wind hazard along the eastern coastline of the United States. Initially, climate change scenarios were coupled with state-of-the-art hurricane genesis, wind field, and tracking models to examine possible changes in hurricane intensity (maximum wind speed) and hurricane size (radius to maximum winds). A number of different postulated climate change models (IPCC scenarios) were considered. Each scenario suggested changes in sea surface temperature (SST), which is the driving parameter in most modern hurricane models. The evolution of hurricane genesis frequency was then considered both independently and jointly with hurricane intensification. State-of-the-art probabilistic event modeling and simulation techniques were used to generate 10,000 years of hurricane events under the 2005 and future climate conditions. The annual maximum wind speed distribution and the joint distribution of maximum wind speed and storm size, under 2005 and future climate scenarios, are then compared. Finally, the evolution of hurricane tracks was examined in an effort to establish a trend over time.

Numerical study of the sensitivity of mangroves in reducing storm surge and flooding to hurricane characteristics in southern Florida

The sensitivity of the mangrove effect on reducing storm surge flooding to hurricane characteristics is investigated by using the numerical model Coastal and Estuarine Storm Tide (CEST). First, the attenuation of storm surge by mangroves is incorporated into the model by updating Manning’s coefficient based on the National Land Cover Dataset (NLCD) 2001. Then CEST is verified by comparing the model results with field observations in South Florida for Hurricane Wilma. Secondly, a set of numerical experiments using synthetic hurricanes with different intensity, forward speed, radius of maximum wind speed and travel direction are conducted for the sensitivity study. Results indicate that storm surge magnitudes and flooding areas are reduced by the mangrove zone more for fast moving hurricanes than slow moving hurricanes in the west coast of South Florida. In addition, increasing hurricane intensity and hurricane size lower the effect of mangroves on attenuating storm surge and reducing the flooding area. The mangrove zone plays a more effective role in reducing flooding areas from hurricanes that travel from east to west than from hurricanes that travel from west to east. The mangrove reduction effect is most sensitive to changes in hurricane forward speed. A 6.7m/s to 2.2m/s decrease in forward speed can result in a decrease in flood area reduction by mangroves that is equivalent to the decrease in flood area reduction by mangroves from Category 3 to 5 hurricanes.

Axisymmetric Hurricane in a Dry Atmosphere: Theoretical Framework and Numerical Experiments

Abstract This paper discusses the possible existence of hurricanes in an atmosphere without water vapor and analyzes the dynamic and thermodynamic structures of simulated hurricane-like storms in moist and dry environments. It is first shown that the “potential intensity” theory for axisymmetric hurricanes is directly applicable to the maintenance of a balanced vortex sustained by a combination of surface energy and momentum flux, even in the absence of water vapor. This theoretical insight is confirmed by simulations with a high-resolution numerical model. The same model is then used to compare dry and moist hurricanes. While it is found that both types of storms exhibit many similarities and fit well within the theoretical framework, there are several differences, most notably in the storm inflow and in the relationship between hurricane size and intensity. Such differences indicate that while water vapor is not necessary for the maintenance of hurricane-like vortices, moist processes directly affect the structure of these storms.

Risk assessment of hurricane winds for Eglin air force base in northwestern Florida, USA

Hurricane winds present a significant hazard for coastal infrastructure. An estimate of the local risk of extreme wind speeds is made using a new method that combines historical hurricane records with a deterministic wind field model. The method is applied to Santa Rosa Island located in the northwestern panhandle region of Florida, USA. Firstly, a hurricane track is created for a landfall location on the island that represents the worst-case scenario for Eglin Air Force Base (EAFB). The track is based on averaging the paths of historical hurricanes in the vicinity of the landfall location. Secondly, an extreme-value statistical model is used to estimate 100-year wind speeds at locations along the average track based again on historical hurricanes in the vicinity of the track locations. Thirdly, the 100-year wind speeds together with information about hurricane size and forward speed are used as input to the HAZUS hurricane wind field model to produce a wind swath across EAFB. Results show a 100-year hurricane wind gust on Santa Rosa Island of 58 (±5) m s−1 (90% CI). A 100-year wind gust at the same location based on a 105-year simulation of hurricanes is lower at 55 m s−1, but within the 90% confidence limits. Based on structural damage functions and building stock data for the region, the 100-year hurricane wind swath results in $574 million total loss to residential and commercial buildings, not including military infrastructure, with 25% of all buildings receiving at least some damage. This methodology may be applied to other coastal areas and adapted to predict extreme winds and their impacts under climate variability and change.

Earth: Cyclones spawn more tornadoes: Increase in hurricane size may explain extra twisters

Earth: Cyclones spawn more tornadoes: Increase in hurricane size may explain extra twisters

Florida Hurricanes and Damage Costs

Florida has been visited by some of the most destructive and devastating hurricanes on record in the United States causing well over $450 billion in damage since the early 20 th century. The value of insured property in Florida against windstorm damage is the highest in the nation and on the rise. The frequency and severity of hurricanes affecting Florida are examined from the best set of available data and the damages are related to characteristics of the storms at landfall. Results show that normalized losses are increasing over time consistent with small increases in hurricane intensity and hurricane size. The best predictor of potential losses is minimum central pressure. Hurricane size alone or in combination with hurricane intensity does not improve on the simpler relationship. An estimate of potential losses from hurricanes can be obtained using a formula involving only a forecast of the minimum pressure at landfall. The ability to estimate potential losses in Florida will increase the ability to estimate losses in other areas of the United States, and will also allow policy makers and insurance companies to provide relevant information to the concerned public.

Statistical Models of Holland Pressure Profile Parameter and Radius to Maximum Winds of Hurricanes from Flight-Level Pressure and H*Wind Data

Abstract In many hurricane risk models the inclusion of the Holland B parameter plays an important role in the risk prediction methodology. This paper presents an analysis of the relationship between B and a nondimensional intensity parameter. The nondimensional parameter includes the strong negative correlation of B with increasing hurricane size [as defined by the radius to maximum winds (RMW)] and latitude as well as a positive correlation with sea surface temperature. A weak positive correlation between central pressure deficit and B is also included in the single parameter term. Alternate statistical models relating B to RMW and latitude are also developed. Estimates of B are derived using pressure data collected during hurricane reconnaissance flights, coupled with additional information derived from the Hurricane Research Division’s H*Wind snapshots of hurricane wind fields. The reconnaissance data incorporate flights encompassing the time period 1977 through 2001, but the analysis was limited to include only those data collected at the 700-hPa-or-higher level. Statistical models relating RMW to latitude and central pressure derived from the dataset are compared to those derived for U.S. landfalling storms during the period 1900–2005. The authors find that for the Gulf of Mexico, using only the landfall hurricanes, the data suggest that there is no inverse relationship between RMW and the central pressure deficit. The RMW data also demonstrate that Gulf of Mexico hurricanes are, on average, smaller than Atlantic Ocean hurricanes. A qualitative examination of the variation of B, central pressure, and radius to maximum winds as a function of time suggests that along the Gulf of Mexico coastline (excluding southwest Florida), during the final 6–24 h before landfall, the hurricanes weaken as characterized by both an increase in central pressure and the radius to maximum winds and a decrease in B. This weakening characteristic of landfalling storms is not evident for hurricanes making landfall elsewhere along the U.S. coastline.

Atlantic Major Hurricanes, 1995–2005—Characteristics Based on Best-Track, Aircraft, and IR Images

Abstract The Atlantic major hurricanes during the period of 1995–2005 are examined using best-track data, aircraft-based observations of central pressure, and infrared (IR) satellite images. There were 45 Atlantic major hurricanes (Saffir–Simpson category 3 or higher) during this 11-yr period, which is well above the long-term average. Descriptive statistics (e.g., average, variability, and range) of various characteristics are presented, including intensity, intensification rate, major hurricane duration, location, storm motion, size, and landfall observations. IR images are shown along with IR-derived quantities such as the digital Dvorak technique intensity and IR-defined cold cloud areas. In addition to the satellite intensity estimates, the associated component IR temperatures are documented. A pressure–wind relationship is evaluated, and the deviations of maximum intensity measurements from the pressure–wind relationship are discussed. The Atlantic major hurricane activity of the 1995–2005 period distinctly exceeds the long-term average; however, the average location where major hurricanes reach maximum intensity has not changed. The maximum intensity for each 1995–2005 Atlantic major hurricane is given both as the highest maximum surface wind (Vmax) and the lowest minimum sea level pressure (MSLP). Comparisons are made to other Atlantic major hurricanes with low MSLP back to 1950. Maximum 24-h intensification rates average 21.1 m s−1 day−1 and range up to 48.8 m s−1 day−1 in terms of Vmax. The largest 24-h MSLP decreases average 34.2 hPa and range from 15 to 97 hPa. Major hurricane duration averages 2.7 days with a maximum of 10 days. Hurricane size, as given by the average radius of gale force wind at maximum intensity, averages 250.8 km and has an extremely large range from 92.5 to 427.4 km.

Hurricane potential intensity from an energetics point of view

AbstractThis article describes an approach to hurricane potential intensity with a model that considers total kinetic energy balance within a hurricane. The major kinetic energy source and sink are the kinetic energy converted from sea surface entropy flux and the surface dissipation, respectively, but the conversion efficiency is radius‐dependent in this model. Also, the internal conversion due to convectively available potential energy (CAPE) as a source is considered. In contrast to previous potential intensity models, energy balance in the entire hurricane is used to get its steady state. With this model, the roles of environmental sea surface temperature (SST), CAPE and some features of the hurricane itself in determining hurricane potential intensity are investigated. The results indicate that existence of CAPE may lead to the steady state (or potential intensity) appreciably different from the otherwise surface entropy flux conversion and surface dissipation balanced state, although CAPE contribution to kinetic energy generation is usually much smaller than that of the surface flux. It is interesting that hurricane potential intensity seems less dependent on the underlying SST than was shown with previous theoretical models. The results also suggest that hurricane size may affect its potential intensity in that larger‐sized hurricanes tend to have higher potential intensities. Copyright © 2004 Royal Meteorological Society