Search Results

You are looking at 1 - 9 of 9 items for

  • Author or Editor: Samuel H. Houston x
  • Refine by Access: All Content x
Clear All Modify Search
Mark D. Powell and Samuel H. Houston

Abstract

No abstract available.

Full access
Mark D. Powell and Samuel H. Houston

Abstract

All available wind data associated with Hurricane Andrew's passage were analysed for periods corresponding to landfall south of Miami and emergence from southwest Florida. At landfall in southeast Florida, maximum sustained 1-min surface wind speeds V M1 reached just over 60 m s−1 in the northern eyewall over land; by the time Andrew exited the Florida peninsula, the peak value of V M1 over land decreased to 40–45 m s−1. Radar reflectivity observations from Tampa and Melbourne could not support an obvious correlation of convective cell development with coastal convergence during landfall on the southeast coast. On the southwest coast, however, convective cell development in the southern eyewall was supported by a coastal convergence maximum. Comparison of the wind swath with two independent Fujita-scale damage maps indicated that peak swath speeds compared well with damage-derived speed equivalents in the worst damaged areas but were higher than equivalents in moderately damaged areas. Comparison of the analysis maximum wind swath with an engineering survey of damaged homes suggests that homes exposed to a wide range of wind directions while subjected to high wind speeds suffered the most damage. Potential real-time applications of wind field products include warning dissemination, emergency management, storm surge and wave forecasting, and wind engineering. Development of damage assessment models for disaster mitigation is addressed from the viewpoint of an electrical utility.

Full access
Mark D. Powell and Samuel H. Houston

Abstract

Hurricanes Erin, Opal, Luis, Marilyn, and Roxanne were the most destructive hurricanes of 1995. At landfall, Luis and Marilyn contained maximum sustained winds (marine exposure) estimated at near 60 and 46 m s−1, respectively. The strongest landfalling storm of the 1995 season, Luis, decreased in intensity from a category 4 to 3 on the Saffir–Simpson scale shortly before the eyewall crossed the Islands of Antigua, Barbuda, St. Kitts-Nevis, St. Barthelemy, St. Martin, and Anguilla. Hurricane Marilyn strengthened as it approached the U.S. Virgin Islands, with St. Thomas bearing the brunt of the north and south eyewall winds of 46 m s−1 (marine exposure) and St. Croix being affected by the relatively weak western eyewall peak winds of 35–40 m s−1 (marine exposure). For Luis and Marilyn only surface winds with marine exposures were analyzed because of unknown small-scale interactions associated with complex island terrain with 500–1000-m elevations. Wind engineering studies suggest that wind acceleration over blunt ridges can increase or “speed up” winds by 20%–80%. Topographic effects were evident in damage debris analyses and suggest that an operational method of assessing terrain-induced wind gusts (such as a scaled down mesoscale model) is needed. After landfall as a marginal hurricane over central Florida, Hurricane Erin regained strength over the Gulf of Mexico with a well-defined radar reflectivity structure. Erin struck the Florida panhandle near Navarre Beach with maximum sustained surface winds of 35–40 m s−1 affecting the Destin–Ft. Walton area. Hurricane Opal made landfall in nearly the identical area as Erin, with maximum sustained surface winds of 40–45 m s−1, having weakened from an intensity of nearly 60 m s−1 only 10 h earlier. Opal was characterized by an asymmetric structure that was likely related to cold front interaction and an associated midlevel southwesterly jet. Roxanne struck Cozumel, Mexico, with sustained surface winds (marine exposure) of 46 s−1, crossed the Yucatan, and meandered in the southwest Gulf of Mexico for several days. While in the Bay of Campeche, Roxanne’s large area of hurricane-force winds disabled a vessel, which lead to the drowning deaths of five oil industry workers. High-resolution wind records are critical to preserving an accurate extreme wind climatology required for assessment of realistic building code risks. Unfortunately, power interruptions to Automated Surface Observing Stations on the U.S. Virgin Islands (St. Croix, St. Thomas) and Destin, Florida, prevented complete wind records of the eyewall passages of Marilyn and Opal, respectively.

Full access
Mark D. Powell, Samuel H. Houston, and Timothy A. Reinhold

Abstract

Hurricane Andrew's landfall in south Florida left a swath of destruction, including many failed anemometer recording systems. Extreme destruction led to exaggerated claims of the range of wind speed that caused such damage. The authors accumulated all available data from surface platforms at heights ranging from 2 to 60 m and reconnaissance aircraft at altitudes near 3 km. Several procedures were used to represent the various types of wind measurements in a common framework for exposure, measurement height, and averaging period. This set of procedures allowed documentation of Andrew's winds in a manner understandable to both meteorologists and wind engineers. The procedures are accurate to ±10% for marine and land observing platforms, and boundary layer model adjustments of flight-level winds to the surface compare to within 20% of the nearest surface measurements. Failure to implement the adjustment procedures may lead to errors of 15%–40%. Quality control of the data is discussed, including treatment of peak wind observations and determination of the radius of maximum winds at the surface.

Full access
Joseph J. Cione, Peter G. Black, and Samuel H. Houston

Abstract

Composite analyses of marine surface observations from 37 hurricanes between 1975 and 1998 show that the difference between the sea surface temperature and the surface air temperature significantly increases just outside the hurricane inner core. This increase in the sea–air contrast is primarily due to a reduction in surface air temperature and is more likely to occur when sea temperatures are at least 27°C. Results show that 90% of the observed cooling occurs 3.25°–1.25° latitude from the hurricane center, well outside the region of strongest surface winds. Since surface pressure only decreases 3 mb over this interval, the ∼2°C drop in air temperature is not a result of adiabatic expansion.

For the subset of observations that contained moisture measurements, surface specific humidity decreased 1.2 g kg−1 4.5°–1.75° latitude from the storm center. This finding suggests that the observed reduction in surface air temperature is not simply a result of near-surface evaporation from sea spray or precipitation. An alternate explanation may be that outside the hurricane inner core, unsaturated convective downdrafts act to dry and evaporatively cool the near-surface environment.

Between 3.25° and 1.25° radius, composite analyses show that low-level inflow is not isothermal, surface moisture is not constant, and the near-surface environment is not in thermodynamic equilibrium with the sea. Calculations based on these observations show that θ e decreases between 4.0° and 1.25° radius and then quickly rises near the inner core as surface pressures fall and specific humidity increases. Surface fluxes of heat and moisture are also observed to significantly increase near the inner core. The largest increase in surface sensible heat flux occurs radially inward of 1.5°, where surface winds are strong and sea–air temperature contrasts are greatest. As a result, the average Bowen ratio is 0.20∼0.5° radius from the composite storm center. This increase in sensible heat flux (in conjunction with near-saturated conditions at low to midlevels) may help explain why average surface air temperatures inside 1.25° radius remain relatively constant, despite the potential for additional cooling from evaporation and adiabatic expansion within the high wind inner core.

Full access
Samuel H. Houston, Wilson A. Shaffer, Mark D. Powell, and Jye Chen

Abstract

Surface wind observations analyzed by the Hurricane Research Division (HRD) were compared to those computed by the parametric wind model used in the National Weather Service Sea, Lake, and Overland Surges from Hurricanes (SLOSH) model’s storm surge computations for seven cases in five recent hurricanes. In six cases, the differences between the SLOSH and HRD surface peak wind speeds were 6% or less, but in one case (Hurricane Emily of 1993) the SLOSH computed peak wind speeds were 15% less than the HRD. In all seven cases, statistics for the modeled and analyzed wind fields showed that for the region of strongest winds, the mean SLOSH wind speed was 14% greater than that of the HRD and the mean inflow angle for SLOSH was 19° less than that of the HRD. The radii beyond the region of strongest winds in the seven cases had mean wind speed and inflow angle differences that were very small. The SLOSH computed peak storm surges usually compared closely to the observed values of storm surge in the region of the maximum wind speeds, except Hurricane Emily where SLOSH underestimated the peak surge. HRD’s observation-based wind fields were input to SLOSH for storm surge hindcasts of Hurricanes Emily and Opal (1995). In Opal, the HRD input produced nearly the same computed storm surges as those computed from the SLOSH parametric wind model, and the calculated surge was insensitive to perturbations in the HRD wind field. For Emily, observation-based winds produced a computed storm surge that was closer to the peak observed surge, confirming that the computed surge in Pamlico Sound was sensitive to atmospheric forcing. Using real-time, observation-based winds in SLOSH would likely improve storm surge computations in landfalling hurricanes affected by synoptic and mesoscale factors that are not accounted for in parametric models (e.g., a strongly sheared environment, convective asymmetries, and stably stratified boundary layers). An accurate diagnosis of storm surge flooding, based on the actual track and wind fields could be supplied to emergency management agencies, government officials, and utilities to help with damage assessment and recovery efforts.

Full access
Jason P. Dunion, Christopher W. Landsea, Samuel H. Houston, and Mark D. Powell

Abstract

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).

Full access
Jason P. Dunion, Samuel H. Houston, Christopher S. Velden, and Mark D. Powell

Abstract

The Cooperative Institute for Meteorological Satellite Studies at the University of Wisconsin—Madison recently (1997 season) began providing real-time Geostationary Operational Environmental Satellite (GOES) low-level cloud-drift winds in the vicinity of tropical cyclones on an experimental basis to the National Oceanic and Atmospheric Administration's (NOAA) Hurricane Research Division (HRD). The cloud-drift winds are derived from sequential high-resolution GOES visible channel imagery. These data were included in many of HRD's real-time tropical cyclone surface wind objective analyses, which were sent to NOAA's National Hurricane Center and the Central Pacific Hurricane Center on an experimental basis during the 1997–2001 hurricane seasons. These wind analyses were used to support the forecasters' tropical cyclone advisories and warnings. The satellite wind observations provide essential low-level coverage in the periphery of the tropical cyclone circulation where conventional in situ observations (e.g., ships, buoys, and Coastal-Marine Automated Network stations) are often widely spaced or nonexistent and reconnaissance aircraft do not normally fly. Though winds derived from microwave channels on polar orbiting satellites provide valuable surface wind data for HRD surface wind analyses, their swath coverage and orbital passes are limited spatially and temporally. GOES low-level visible (GLLV) winds offer nearly continuous spatial and temporal coverage in the western Atlantic and eastern Pacific basins. The GLLV winds were extrapolated to the surface using a planetary boundary layer model developed at HRD. These surface-adjusted satellite data were used in real-time surface wind analyses of 1998 Hurricane Georges, as well as in poststorm analyses of 1996 Hurricane Lili and 1997 Tropical Storm Claudette. The satellite observations often helped to define the spatial extent of the 17.5 m s−1 (34 kt) surface wind radii and also redefined the 25.7 m s−1 (50 kt) wind radius for one case. Examples of the impact of these data on real-time hurricane surface wind fields provided to the NHC will be discussed.

Full access
Robert W. Burpee, Sim D. Aberson, Peter G. Black, Mark DeMaria, James L. Franklin, Joseph S. Griffin, Samuel H. Houston, John Kaplan, Stephen J. Lord, Frank D. Marks Jr., Mark D. Powell, and Hugh E. Willoughby

The Hurricane Research Division (HRD) is NOAA's primary component for research on tropical cyclones. In accomplishing research goals, many staff members have developed analysis procedures and forecast models that not only help improve the understanding of hurricane structure, motion, and intensity change, but also provide operational support for forecasters at the National Hurricane Center (NHC). During the 1993 hurricane season, HRD demonstrated three important real-time capabilities for the first time. These achievements included the successful transmission of a series of color radar reflectivity images from the NOAA research aircraft to NHC, the operational availability of objective mesoscale streamline and isotach analyses of a hurricane surface wind field, and the transition of the experimental dropwindsonde program on the periphery of hurricanes to a technology capable of supporting operational requirements. Examples of these and other real-time capabilities are presented for Hurricane Emily.

Full access