Hurricane Research Division
FY-2003 Publications
(October 1, 2002-September 30, 2003)
(names of HRD authors appear in capital letters)
	[1]	ABERSON, S.D.  Targeted observations to improve operational tropical cyclone track forecast guidance.  Monthly Weather Review, 131(8):1613-1628 (2003).
Since 1997, the Tropical Prediction Center and the Hurricane Research Division have conducted operational synoptic surveillance missions with a Gulfstream IV-SP jet aircraft to improve numerical forecast guidance. Due to limited aircraft resources, optimal observing strategies for these missions must be developed. In the current study, the most rapidly growing modes are represented by areas of large forecast spread in the NCEP bred-vector ensemble forecasting system. The sampling strategy requires sampling of the entire target region with regularly spaced dropwindsonde observations. Three dynamical models were employed in testing the targeting and sampling strategies. With the assimilation into the numerical guidance of all the observations gathered during the surveillance missions, only the 12-h Geophysical Fluid Dynamics Laboratory Hurricane Model forecast showed statistically significant improvement. Assimilation of only the subset of data from the subjectively found fully sampled target regions produced a statistically significant reduction of the track forecast errors of up to 25% within the critical first two days of the forecast. This is comparable with the cumulative business-as-usual improvement expected over 18 yr.
	[2]	ABERSON, S.D.  Two years of operational hurricane synoptic surveillance.  Weather and Forecasting, 17(5):1101-1110 (2002).
In 1997, the National Hurricane Center and the Hurricane Research Division began operational synoptic surveillance missions with the Gulfstream IV-SP jet aircraft to improve the numerical guidance for hurricanes that threaten the continental United States, Puerto Rico, the Virgin Islands, and Hawaii. During the first two years, 24 missions were conducted. Global positioning system dropwindsondes were released from the aircraft at 150-200 km intervals along the flight track in the environment of each tropical cyclone to obtain profiles of wind, temperature, and humidity from flight level (nearly 150 hPa) to the surface. The observations were processed and formatted aboard the aircraft and sent to NCEP to be ingested into the Global Data Assimilation System, which subsequently served as initial and boundary conditions for a number of numerical models that forecast the track and intensity of tropical cyclones. The current study is an attempt to mimic this process to assess the impact of these operational missions on the numerical guidance. Although the small number of missions flown in 1997 showed error reductions of as much as 32%, the improvements seen in the two-year sample are not promising. The additional dropwindsonde data from the synoptic surveillance missions provided statistically significant improvements in the GFDL forecasts only at 12 h. The “VBAR” and Global Forecast System (AVN) forecasts were not significantly improved at any forecast time. Further examination suggests that the AVN synthetic vortex procedure, combined with difficulty in the quantification of the current storm-motion vector operationally, may have caused the mediocre improvements. Forecast improvements of 14-24% in GFDL forecasts are shown in the subset of cases in which the synthetic vortex data do not seem to be a problem. Improvements in the landfall forecasts are also seen in this subset of cases. A reassessment of tropical cyclone vortex initialization schemes used by forecast centers and numerical modelers may be necessary.
	[3]	ABERSON, S.D., and C.R. Sampson.  On the predictability of tropical cyclone tracks in the northwest Pacific basin.  Monthly Weather Review, 131(7):1491-1497 (2003).
A new northwest Pacific climatology and persistence (CLIPER) model is derived with historical tropical cyclone tracks during the satellite and aircraft reconnaissance era (1970-1995). The new CLIPER extends the forecasts from three to five days and exhibits smaller forecast biases than the previous CLIPER, although forecast errors are comparable. The new model is based on more accurate historical tropical cyclone track data, and a simpler derivation of the regression equations, than is the old model. Nonlinear systems analysis shows that the predictability timescale in which the average errors increase by a factor e is just over 15 h, which is about the same as that calculated by similar methods near Australia and in the North Atlantic. This suggests that five-day tropical cyclone track forecasts may be beneficial, assuming small initial errors; therefore, a CLIPER model extended to five days is needed as a baseline to measure the forecast skill.
	[4]	CIONE, J.J., and E.W. UHLHORN.  Sea surface temperature variability in hurricanes: Implications with respect to intensity change.  Monthly Weather Review, 131(8):1783-1796 (2003).
Scientists at NOAA's Hurricane Research Division recently analyzed the inner-core upper-ocean environment for 23 Atlantic, Gulf of Mexico, and Caribbean hurricanes between 1975 and 2002. The interstorm variability of sea surface temperature (SST) change between the hurricane inner-core environment and the ambient ocean environment ahead of the storm is documented using airborne expendable bathythermograph (AXBT) observations and buoy-derived archived SST data. The authors demonstrate that differences between inner-core and ambient SST are much less than poststorm, “cold wake” SST reductions typically observed (i.e., 0E-2EC versus 4E-5EC). These findings help define a realistic parameter space for storm-induced SST change within the important high-wind, inner-core hurricane environment. Results from a recent observational study yielded estimates of upper-ocean heat content, upper-ocean energy extracted by the storm, and upper-ocean energy utilization for a wide range of tropical systems. Results from this analysis show that, under most circumstances, the energy available to the tropical cyclone is at least an order of magnitude greater than the energy extracted by the storm. This study also highlights the significant impact that changes in inner-core SST have on the magnitude of air-sea fluxes under high-wind conditions. Results from this study illustrate that relatively modest changes in inner-core SST (order 1EC) can effectively alter maximum total enthalpy (sensible plus latent heat) flux by 40% or more. The magnitude of SST change (ambient minus inner core) was statistically linked to subsequent changes in storm intensity for the 23 hurricanes included in this research. These findings suggest a relationship between reduced inner-core SST cooling (i.e., increased inner-core surface enthalpy flux) and tropical cyclone intensification. Similar results were not found when changes in storm intensity were compared with ambient SST or upper-ocean heat content conditions ahead of the storm. Under certain circumstances, the variability associated with inner-core SST change appears to be an important factor directly linked to the intensity change process.
	[5]	DUNION, J.P., C.W. LANDSEA, S.H. Houston, and M.D. POWELL.  A reanalysis of the surface winds for Hurricane Donna of 1960.  Monthly Weather Review, 131(9):1992-2011 (2003).
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).
	[6]	Franklin, J.L., M.L. BLACK, and K. Valde.  GPS dropwindsonde wind profiles in hurricanes and their operational implications.  Weather and Forecasting, 18(1):32-44 (2003).
The recent development of the global positioning system (GPS) dropwindsonde has allowed the wind and thermodynamic structure of the hurricane eyewall to be documented with unprecedented accuracy and resolution. In an attempt to assist operational hurricane forecasters in their duties, dropwindsonde data have been used in this study to document, for the first time, the mean vertical profile of wind speed in the hurricane inner core from the surface to the 700-hPa level, the level typically flown by reconnaissance aircraft. The dropwindsonde-derived mean eyewall wind profile is characterized by a broad maximum centered 500 m above the surface. In the frictional boundary layer below this broad maximum, the wind decreases nearly linearly with the logarithm of the altitude. Above the maximum, the winds decrease because of the hurricane’s warm core. These two effects combine to give a surface wind that is, on average, about 90% of the 700-hPa value. The dropwindsonde observations largely confirm recent operational practices at the National Hurricane Center for the interpretation of flight-level data. Hurricane wind profiles outside of the eyewall region are characterized by a higher level of maximum wind, near 1 km, and a more constant wind speed between 700 hPa and the top of the boundary layer. Two factors that likely affect the eyewall profile structure are wind speed and vertical motion. A minimum in surface wind adjustment factor (i.e., relatively low surface wind speeds) was found when the wind near the top of the boundary layer was between 40 and 60 m s-1. At higher wind speeds, the fraction of the boundary layer wind speed found at the surface increased, contrary to expectation. Low-level downdrafts and enhanced vertical motion generally were also associated with higher relative surface winds. These results may be of interest to engineers concerned with building codes, to emergency managers who may be tempted to use high-rise buildings as a “refuge of last resort” in coastal areas, and to those people on locally elevated terrain. The top of a 25-story coastal high-rise in the hurricane eyewall will experience a mean wind that is about 17% higher (or one Saffir-Simpson hurricane-scale category) than the surface or advisory value. For this reason, residents who must take refuge in coastal high-rises should generally do so at the lowest levels necessary to avoid storm surge.
	[7]	Gedzelman, S., E. Hindman, X. Zhang, J. Lawrence, J.F. GAMACHE, M.L. BLACK, R.A. BLACK, J.P. DUNION, and H.E. WILLOUGHBY.  Probing hurricanes with stable isotopes of rain and water vapor.  Monthly Weather Review, 131(6):1112-1127 (2003).
Rain and water vapor were collected during flights in Hurricanes Olivia (1994), Opal (1995), Marilyn (1995), and Hortense (1995) and analyzed for their stable isotopic concentrations, or ratios, H218O:H2O and HDO:H2O. The spatial patterns and temporal changes of isotope ratios reflect details of a hurricane's structure, evolution, microphysics, and water budget. At all flight levels over the sea (850-475 hPa) the lowest isotope ratios occur in or near regions of stratiform rains between about 50 and 250 km from the eye. Isotope ratios are higher in the eyewall and were particularly high in the crescent-shaped eyewall of Hurricane Opal at a time when no rain was falling over a large area near the storm center. In Hurricane Olivia, isotope ratios decreased from 24 to 25 September after vertical and radial circulation weakened. A two-layer isotope model of a radially symmetric hurricane simulates these features. The low isotope ratios are caused by fractionation in extensive, thick, precipitating clouds with predominantly convergent low-level flow accompanied by removal of heavy isotopes by falling raindrops. Evaporation and isotope equilibration of sea spray increase isotope ratios of the ambient vapor and produce a deuterium excess or enrichment of D relative to 18O that increases with decreasing relative humidity and increasing wind speed. Model results show that sea spray supplies the eyewall with up to 50% of its water vapor and is largely responsible for its high isotope ratios.
	[8]	Kollias, P., B.A. Albrecht, and F.D. MARKS.  Cloud radar observations of vertical drafts and microphysics in convective rain.  Journal of Geophysical Research, 108(D2):4053 doi:10.1029/2001JD002033 (2003).
Observations of convective precipitation using a 94-GHz cloud radar are presented.  Due to Mie scattering, the Doppler power spectra collected at vertical incidence contains characteristics of the scatterers (hydrometeors). These characteristics are used for the retrieval of the vertical air motion and the associated raindrop size distribution in an attempt to accurately map the time-height structure of the vertical air motion and raindrop fields within intense convective precipitation. The data provide strong evidence of the interaction between draft intensity and raindrop size distribution and highlight the variability of convective precipitation at small scales. Horizontal sorting of the raindrops caused by the air motion is documented. Signal attenuation measured at 94 GHz is shown to be well correlated to rainfall rates. The observations demonstrate the capability of 94-GHz cloud radars for studies of precipitation processes at low altitudes even under intense convective conditions.
	[9]	Kollias, P., B.A. Albrecht, and F.D. MARKS.  Why Mie?  Bulletin of the American Meteorological Society, 83(10):1471-1483 (2002).
This article demonstrates an innovative method for the observation of vertical air motion and raindrop size distribution in precipitation using a 94-GHz Doppler radar. The method is particularly appealing since it is based on fundamental physics, the scattering of microwave radiation by large particles (Mie scattering). The technique was originally proposed in 1988 by Dr. Roger Lhermitte, who ironically pioneered the development of 94-GHz Doppler radars for the study of nonprecipitating clouds. Since then, no real effort for the evaluation and demonstration of the technique was undertaken. In this article, observations from stratiform rain are presented to illustrate the potential and accuracy of the method. The retrievals from this technique provide vertical air motion to an accuracy of 5-10 cm s-1. Despite attenuation, the Doppler velocity measurements remain unbiased and the data revealed high-resolution kinematical and microphysical structures within the stratiform precipitation for the first time. This article will hopefully expose the potential of this technique to the meteorological community and will serve as another example of the visionary contributions that Dr. Lhermitte has made to radar meteorology.
	[10]	Lee, W.-C., F.D. MARKS, and C. Walther.  Airborne Doppler radar data analysis workshop.  Bulletin of the American Meteorological Society, 84(8):1063-1075 (2003).
The Airborne Doppler Radar Data Analysis Workshop, sponsored by the Atmospheric Technology Division (ATD) of the National Center for Atmospheric Research (NCAR), was the first to focus on analyzing airborne Doppler radar data. The workshop (held 13-16 March 2000 at NCAR) aimed to (1) summarize the current airborne Doppler radar data analysis techniques, and (2) promote the use of airborne Doppler radar data in the atmospheric sciences community. The workshop also intended to encourage new users to analyze this Doppler data and to provide a forum for experienced users to exchange ideas and discuss problems related to analyzing the data. It also provided a forum to train the users in planning future airborne Doppler radar programs. Graduate students, recent PhDs, faculty and researchers participants—the leading experts in the field—covered the theory of airborne Doppler radar, experiment design, standard data analysis procedures and software, and recently developed analysis techniques. Eight working groups were organized among the participants to analyze preselected airborne Doppler radar datasets collected in past experiments using the standard software available from NCAR. Each working group used standard data analysis procedures to obtain dual-Doppler radar winds from raw airborne Doppler radar data.
	[11]	MARKS, F.D.  Hurricanes.  In Encyclopedia of Atmospheric Sciences, Elsevier Science Ltd., London, UK, 942-966 (2003).
No abstract.
	[12]	Mo, Q., A.G. Detwiler, J. Hallett, and R.A. BLACK.  Horizontal structure of the electric field in the stratiform region of an Oklahoma mesoscale convective system.  Journal of Geophysical Research, 108(D7):4225, doi:10.1029/2001JD001140 (2003).
This analysis combines vertical electric field components Ez observed by two research aircraft flying horizontally at two levels, with vertical soundings of thermodynamic parameters and Ez made by five balloons, to produce a quasi-three-dimensional view of the space charge distribution in the trailing stratiform cloud region behind a mesoscale convective system (MCS) that developed in central Oklahoma late in the afternoon of 2 June 1991. The balloons were launched serially at one-hour intervals from two sites separated by 80 km along a north-south line as the MCS moved eastward, yielding two east-west time-height cross-sections of the Ez structure within the quasi-steady state trailing stratiform region behind the MCS. The balloon measurements are consistent with a vertical stack of five rearward- and downward-sloping horizontal sheets of charge of alternating polarity, beginning at the bottom with a negative charge layer below the 0EC level and a positive layer near the 0EC level. This structure persisted for more than 2 hours. The two aircraft flew back and forth along a north-south line through the balloon launch sites during the balloon launch period. Aircraft measurements demonstrated that the vertical electric field (Ez) at constant altitude varied in the north-south direction. The peak magnitudes of Ez deduced from the airborne instrument systems agreed with the magnitudes deduced from the balloon measurements at the aircraft altitudes of 4.5 km and 5.8 km AGL. Rapid reversals in polarity of Ez with peak magnitude >50 kV m-1 observed by the aircraft at 4.5 km, just above the 0EC level, confirms the thin concentrated positive charge layer observed there by balloons and suggests that this charge layer is undulating above and below 4.5 km altitude, at least in the north-south direction. Microphysically, this layer contained large aggregates and pockets of low cloud liquid water concentration. At the 5.8 km level, the polarity of Ez was always positive but the magnitude varied from zero to 25 kV m-1. Aircraft-observed Ez at both altitudes varied on horizontal scales of ~10 km or greater at both levels, suggesting that the charge density derived using the one-dimensional infinite-layer Gauss's law approximation applied to the balloon soundings of Ez is valid in this study. These observations show that layers of charge can persist for hours as they advect rearward in a storm-relative sense, possibly due to continuing in situ charge separation, and/or due to weak dispersion, slow recombination, and slow settling of charge attached to low mobility low terminal velocity ice hydrometeors.
	[13]	OOYAMA, K.V.  The cubic-spline transform method: Basic definitions and tests in a 1D single domain.  Monthly Weather Review, 130(10):2392-2415 (2002).
The purpose of the paper is to describe the technical details of a numerical method that combines the cubic-spline representation of spatial variables in a finite domain with the logistics of the spectral transform method for the time integration of nonlinear meteorological equations. The reason for developing the method lies in its application to two-way interacting nested models of the atmosphere. When compared with the gridpoint representation, the cubic-spline representation allows direct evaluation of derivatives in the model equations, and leads to a substantial reduction of shortwave dispersion of advecting and propagating waves. When compared with the Fourier spectral representation, the cubic B-splines as basis functions provide simple but exact means of implementing a variety of boundary conditions that are needed at the domain interfaces, as well as at natural boundaries. A sharp (sixth order) low-pass filter, which is built into the cubic-spline transform, effectively eliminates adverse nonlinear accumulation of small-scale errors near the resolution limit. These features, critically important to noise-free nesting, are defined and analyzed in this paper in the simpler context of a single 1D domain. The actual procedures for two-way interactive nesting will be presented in a subsequent paper.
	[14]	Owens, B.F., and C.W. LANDSEA.  Assessing the skill of operational Atlantic seasonal tropical cyclone forecasts.  Weather and Forecasting, 18(1):45-54 (2003).
Since 1984, William Gray of Colorado State University and a team of researchers have been issuing seasonal tropical cyclone forecasts for the North Atlantic Ocean. Prior to this, little work had been done in the area of long-term tropical cyclone forecasting because researchers saw minimal potential skill in any prediction models and no obvious benefits to be gained. However, seasonal forecasts have been attracting more attention as economic and insured losses from hurricane-related catastrophes rose sharply during recent decades. Initially, the forecasts issued by Gray consisted of output from simple statistical prediction models. Over time, the models became increasingly more complex and sophisticated, with new versions being introduced in 1992, 1993, 1994, 1996, and 1997. In addition, based on a combination of experience with the statistical models and other qualitative considerations such as examinations of analog years, the statistical forecasts were modified to create adjusted seasonal forecasts. This analysis assessed the skill demonstrated, if any, of both the statistical and adjusted forecasts over the benchmarks of climatology and persistence and examined whether the adjusted forecasts were more accurate than the statistical forecasts. The analysis indicates that, over the past 18 years, both the statistical and adjusted forecasts demonstrated some skill over climatology and persistence. There is also evidence to suggest that the adjusted forecast was more skillful than the statistical model forecast.
	[15]	Pielke, R.A., J. Rubiera, C. LANDSEA, M.L. Fernandez, and R. Klein.  Hurricane vulnerability in Latin America and the Caribbean: Normalized damage and loss potentials.  Natural Hazards Review, 4(3):101-114 (2003).
In late October 1998, the remnants of Hurricane Mitch stalled over Honduras and Nicaragua, killing more than 10,000 people and causing as much as $8.5 billion in damage. While Central America and the Caribbean have a history of natural disasters, the fatalities and destruction caused by Mitch were the greatest in at least several decades, prompting many questions including: What accounts for the extent of these losses? Is Mitch a harbinger of future disasters in the region? and What might be done in response? This paper seeks to shed light on these questions by examining the historical and geographic context of hurricane vulnerability in Latin America and the Caribbean. The paper examines trends in economic and other societal factors that increase vulnerability to hurricanes in Central America and the Caribbean and includes a case study of normalized hurricane losses in Cuba made possible by newly collected damage data published herein. The paper places its findings into the context of policies related to climate change and natural hazards.
	[16]	POWELL, M.D., P.J. Vickery, and T.A. Reinhold.  Reduced drag coefficient for high wind speeds in tropical cyclones.  Nature, 422:279-283 (2003).
The transfer of momentum between the atmosphere and the ocean is described in terms of the variation of wind speed with height and a drag coefficient that increases with sea surface roughness and wind speed. But direct measurements have only been available for weak winds; momentum transfer under extreme wind conditions has therefore been extrapolated from these field measurements. Global Positioning System sondes have been used since 1997 to measure the profiles of the strong winds in the marine boundary layer associated with tropical cyclones. Here we present an analysis of these data, which show a logarithmic increase in mean wind speed with height in the lowest 200 m, maximum wind speed at 500 and a gradual weakening up to a height of 3 km. By determining surface stress, roughness length, and neutral stability drag coefficient, we find that surface momentum flux levels off as the wind speeds increase above hurricane force. This behavior is contrary to surface flux parameterizations that are currently used in a variety of modeling applications, including hurricane risk assessment and prediction of storm motion, intensity, waves, and storm surges.
	[17]	ROGERS, R.F., S. Chen, J. Tenerelli, and H.E. WIILLOUGHBY.  A numerical study of the impact of vertical shear on the distribution of rainfall in Hurricane Bonnie (1998).  Monthly Weather Review, 131(8):1577-1599 (2003).
Despite the significant impacts of torrential rainfall from tropical cyclones at landfall, quantitative precipitation forecasting (QPF) remains an unsolved problem. A key task in improving tropical cyclone QPF is understanding the factors that affect the intensity and distribution of rainfall around the storm. These include the storm motion, topography, and orientation of the coast, and interactions with the environmental flow. The combination of these effects can produce rainfall distributions that may be nearly axisymmetric or highly asymmetric and rainfall amounts that range from 1 or 2 cm to >30 cm.  This study investigates the interactions between a storm and its environmental flow through a numerical simulation of Hurricane Bonnie (1998) that focuses on the role of vertical wind shear in governing azimuthal variations of rainfall. The simulation uses the high-resolution nonhydrostatic fifth-generation Pennsylvania State University-NCAR Mesoscale Model (MM5) to simulate the storm between 0000 UTC 22 August and 0000 UTC 27 August 1998. During this period significant changes in the vertical shear occurred in the simulation. It changed from strong west-southwesterly, and across track, to much weaker south-southwesterly, and along track. Nearly concurrently, the azimuthal distribution of convection changed from a distinct wavenumber-1 pattern to almost azimuthally symmetric by the end of the time period. The strongest convection in the core was generally located on the downshear left side of the shear vector when the shear was strong. The azimuthal distributions and magnitudes of low-level radial inflow, reflectivity, boundary layer divergence, and low-level vertical motion all varied consistently with the evolution of the vertical shear. Additionally, the vortex showed a generally downshear tilt from the vertical. The magnitude of the tilt correlated well with changes in magnitude of the environmental shear. The accumulated rainfall was distributed symmetrically across the track of the storm when the shear was strong and across track, and it was distributed asymmetrically across the track of the storm when the shear was weak and along track.
	[18]	UHLHORN, E.W., and P.G. BLACK.  Verification of remotely sensed sea surface winds in hurricanes.  Journal of Atmospheric and Oceanic Technology, 20(1):99-116 (2003).
Surface winds in hurricanes have been estimated remotely using the Stepped-Frequency Microwave Radiometer (SFMR) from the NOAA WP-3D aircraft for the past 15 years. Since the use of the GPS dropwindsonde system in hurricanes was first initiated in 1997, routine collocated SFMR and GPS surface wind estimates have been made. During the 1998, 1999, and 2001 hurricane seasons, a total of 249 paired samples were acquired and compared. The SFMR equivalent 1-min mean, 10-m level neutral stability winds were found to be biased high by 2.3 m s-1 relative to the 10-m GPS winds computed from an estimate of the mean boundary layer wind. Across the range of wind speeds from 10 to 60 m s-1, the rmse was 3.3 m s-1. The bias was found to be dependent on storm quadrant and independent of wind speed, a result that suggests a possible relationship between microwave brightness temperatures and surface wave properties. Tests of retrieved winds’ sensitivities to sea surface temperature, salinity, atmospheric thermodynamic variability, and surface wind direction indicate wind speed errors of less than 1 m s-1 above 15 m s-1.