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.

Modeling the Impacts of the Large-Scale Atmospheric Environment on Inland Flooding during the Landfall of Hurricane Floyd (1999)

The contribution of the large-scale atmospheric environment to precipitation and flooding during Hurricane Floyd was investigated in this study. Through the vortex removal technique in the Weather Research and Forecasting (WRF) model, the vortex associated with Hurricane Floyd (1999) was mostly removed in the model initial conditions and subsequent integration. Results show that the environment-induced precipitation can account for as much as 22% of total precipitation in the innermost model domain covering North Carolina coastal area and 7% in the focused hydrological study area. The high-resolution precipitation data from the WRF model was then used for input in a hydrological model to simulate river runoff. Hydrological simulation results demonstrate that without the tropical systems and their interactions with the large-scale synoptic environment the synoptic environment would only contribute 10% to the total discharge at the Tarboro gauge station. This suggests that Hurricane Floyd and Hurricane Dennis preceding it, along with the interactions between these tropical systems and the large-scale environment, have contributed to the bulk (90%) of the record amount of flood water in the Tar-Pamlico River Basin.

Vertical Velocity and Microphysical Distributions Related to Rapid Intensification in a Simulation of Hurricane Dennis (2005)

A 1-km Weather Research and Forecasting model simulation of Hurricane Dennis was used to identify precursors in vertical velocity and latent heating distributions to rapid intensification (RI). Although the observed structure qualitatively replicated data obtained during P-3 and Earth Resources-2 (ER-2) flights, the simulated reflectivity was overestimated. During the 6 h preceding RI, defined as 0000 UTC 8 July 2005 close to the time of simulated maximum central pressure deepening, the asymmetric convection transformed into an eyewall with the maximum 10-m wind speed increasing by 16 m s−1. Contour by frequency altitude diagrams showed unique changes in the breadth of simulated vertical velocity (w) distributions before and after RI. Outliers of w distributions at 14 km preceded RI onset, whereas the increase in w outliers at 6 km lagged it. Prior to RI there was an increase in the upward flux of hydrometeors between 10 and 15 km, with increased contributions from w > 6 m s−1. Increases in lower-level updraft airmass fluxes did not lead RI, but the 14-km positive w outliers were better indicators of RI onset than positive w averages. The area of convective bursts did not strongly increase before RI, but it continually increased after RI. Latent heating was dominated by contributions from w < 2 m s−1, meaning increases in positive w outliers before RI did not cause the increase in latent heating seen during RI. The location of convective bursts and outliers of positive and negative w distributions contracted toward the eye as the simulated Dennis intensified.

On the Vertical Decay Rate of the Maximum Tangential Winds in Tropical Cyclones

In this study, it is shown that the maximum tangential winds within tropical cyclones decrease with height at a percentage rate that is nearly independent of both the maximum wind speed and the radius of maximum winds (RMW). This can be seen by normalizing the profiles of maximum tangential winds Vmax by their respective values at 2-km height. From Doppler radar analyses, profiles of maximum normalized tangential wind Vmaxnorm are found to share a common shape, despite spanning a great range of intensities. There is a systematic dependence of Vmaxnorm on intensity and size, but it is shown to be small, and the mean profile of Vmaxnorm can be used to accurately “predict” the individual profiles of Vmax. Using Emanuel’s steady-state analytical vortex model, it is shown that Vmaxnorm is essentially independent of the size of the RMW. It is shown mathematically that the near independence of Vmaxnorm from size is due to the facts that the RMW is nearly a surface of constant absolute angular momentum M and that its outward slope increases linearly with radius. As the slope of the RMW is not a function of intensity, Vmaxnorm is also nearly independent of intensity in theory, and this is confirmed using Emanuel’s simple time-dependent model. In contrast to intensity, it is shown that Vmaxnorm increases with potential intensity. A suite of idealized simulations using the Weather Research and Forecasting model (WRF) are used to further examine the manner in which the maximum winds change with height. Above 2-km height, vertical profiles of Vmaxnorm are nearly independent of both intensity and size. Occasional deviations from this near-universal profile in these simulations are due to unbalanced winds, and it is proposed that this is the cause of occasional observations of maximum winds that are nearly constant with height through the midtroposphere, as in Hurricane Gloria (1985) and Hurricane Dennis (2005).

Factors determining the abundance, distribution and population size–structure of the penshellPinna carnea

Surveys conducted in the south-western Dominican Republic showed that the penshellPinna carneais a consistent component of seagrass beds and is absent in adjacent sandflats. Population densities were low (0.012–0.076·m−2) and the size–structure skewed towards large individuals. Trials with different types of substrata in caged spat collectors, involving a combination of sand, seagrass blades and roots, and an artificial treatment by itself, indicated no settlement preference for any of the substrata tested. Comparison of additional spat collectors (caged and uncaged) indicated high predation losses (84%) for recently settled penshells. Experiments with penshells measuring 10–30, 50–70 and 90–110 mm (anterior to posterior dorsal tip) transplanted to plots in a seagrass bed and sandflat showed that predation losses decreased with increasing size and were much less in seagrass than in the sandflat. In 10-day trials, survival in the three size-groups was 27-fold greater in the seagrass bed than on the sandflat. During 3-day trials in the sandflat, survival increased from 6% for 50–100 mm penshells to 93% for 150–170 mm penshells. At the end of 100-day trials, during which the study area was subjected to Hurricane Dennis, the only surviving penshells were large individuals (90–110 mm) that had been transplanted to the seagrass bed. All individuals transplanted to the sandflat went missing. Growth measurements showed that small penshells grow rapidly (up to 2.2 mm·d−1), but the growth rate drops markedly at ~150 mm. Rapid juvenile growth may be a strategy for reducing the period of high vulnerability to predators. The high proportion of large individuals in the population likely represents the accumulation of successive recruitments as growth slows in older penshells.Pinna carneais mainly restricted to seagrass beds because they provide more protection from predators than adjacent habitats. Moreover, the consolidation of sediments in seagrass beds by roots and algal rhizoids provides a degree of protection from physical disturbances such as hurricanes. The advantages provided by the seagrass habitat come at a cost because we detected a mortality factor in the seagrass bed (possibly related to the ~3-fold higher silt load) that was absent on the sandflat.

Multiscale Observations of Hurricane Dennis (2005): The Effects of Hot Towers on Rapid Intensification

A synthesis of remote sensing and in situ observations throughout the life cycle of Hurricane Dennis (2005) during the NASA Tropical Cloud Systems and Processes (TCSP) experiment is presented. Measurements from the ER-2 Doppler radar (EDOP), the Advanced Microwave Sounding Unit (AMSU), airborne radiometer, and flight-level instruments are used to provide a multiscale examination of the storm. The main focus is an episode of deep convective bursts (“hot towers”) occurring during a mature stage of the storm and preceding a period of rapid intensification (11-hPa pressure drop in 1 h 35 min). The vigorous hot towers penetrated to 16-km height, had maximum updrafts of 20 m s−1 at 12–14-km height, and possessed a strong transverse circulation through the core of the convection. Significant downdrafts (maximum of 10–12 m s−1) on the flanks of the updrafts were observed, with their cumulative effects hypothesized to result in the observed increases in the warm core. In one ER-2 overpass, subsidence was transported toward the eye by 15–20 m s−1 inflow occurring over a deep layer (0.5–10 km) coincident with a hot tower. Fourier analysis of the AMSU satellite measurements revealed a large shift in the storm’s warm core structure, from asymmetric to axisymmetric, ∼12 h after the convective bursts began. In addition, flight-level wind calculations of the axisymmetric tangential velocity and inertial stability showed a contraction of the maximum winds and an increase in the stiffness of the vortex, respectively, after the EDOP observations. The multiscale observations presented here reveal unique, ultra-high-resolution details of hot towers and their coupling to the parent vortex, the balanced dynamics of which can be generally explained by the axisymmetrization and efficiency theories.

Impact of Airborne Doppler Radar Data Assimilation on the Numerical Simulation of Intensity Changes of Hurricane Dennis near a Landfall

Accurate forecasting of a hurricane’s intensity changes near its landfall is of great importance in making an effective hurricane warning. This study uses airborne Doppler radar data collected during the NASA Tropical Cloud Systems and Processes (TCSP) field experiment in July 2005 to examine the impact of airborne radar observations on the short-range numerical simulation of hurricane track and intensity changes. A series of numerical experiments is conducted for Hurricane Dennis (2005) to study its intensity changes near a landfall. Both radar reflectivity and radial velocity–derived wind fields are assimilated into the Weather Research and Forecasting (WRF) model with its three-dimensional variational data assimilation (3DVAR) system. Numerical results indicate that the radar data assimilation has greatly improved the simulated structure and intensity changes of Hurricane Dennis. Specifically, the assimilation of radar reflectivity data shows a notable influence on the thermal and hydrometeor structures of the initial vortex and the precipitation structure in the subsequent forecasts, although its impact on the intensity and track forecasts is relatively small. In contrast, assimilation of radar wind data results in moderate improvement in the storm-track forecast and significant improvement in the intensity and precipitation forecasts of Hurricane Dennis. The hurricane landfall, intensification, and weakening during the simulation period are well captured by assimilating both radar reflectivity and wind data.