Background on the HRD Surface Wind Analysis System
Tropical cyclones are monitored globally by space-, aircraft-, land-
and marine-based observing systems. Advances in computing and
communications have made it possible to obtain these observations in
near real-time. However, scientists involved in operational
forecasting and basic and applied research on hurricanes have few
tools that enable real-time interaction with, and analysis of,
observations gathered in tropical cyclones. In the Atlantic, Eastern
Pacific, and Central Pacific Ocean basins, hurricane wind fields are
determined subjectively based on the specialist's interpretation of
flight-level reconnaissance data, satellite observations,
pressure-wind relationships and available surface data. These fields
are represented by text portions of the official forecast product as
radii (from the storm center) of 34 kt, 50 kt, and hurricane force
winds in four compass quadrants relative to north. Until recently, no
operational objective method has been available for assimilating and
synthesizing disparate observations into a consistent wind field.
The HRD Surface Wind Analysis System is a research tool designed to
fill this need.
The HRD approach to hurricane wind analysis evolved from a series of
peer-reviewed, scientific publications analyzing landfalls of major
hurricanes including Frederic of 1979, Alicia of 1983, Hugo of 1989,
and Andrew of 1992 (Powell et al., 1991, Powell and Houston, 1996,
1998, Powell et al., 1998). In our paper describing Hurricane Hugo's
landfall, we developed the concept of a system for conducting
real-time analysis of hurricane wind fields. We were in the process
of constructing this system when Hurricane Andrew struck. The system
was first used in real-time during Hurricane Emily in 1993 (Burpee
et al., 1994). Since 1994, HRD wind analyses have been conducted on
an experimental basis to create real time hurricane wind field
guidance for forecasters at the National Hurricane Center. During
Hurricane landfall episodes, HRD scientists work side by side
hurricane specialists at NHC analyzing wind observations on a regular
3 or 6 hour schedule consistent with NHC's warning and forecast
An HRD wind analysis requires the input of all available surface
weather observations (e.g., ships, buoys, coastal platforms, surface
aviation reports, reconnaissance aircraft data adjusted to the
surface, etc.). Observational data are downloaded on a regular
schedule and then processed to fit the analysis framework. This
includes the data sent by NOAA P3 and G4 research aircraft during the
HRD hurricane field program as well as U.S. Air Force Reserves
(AFRES) C-130 reconnaissance aircraft, remotely sensed winds from the
polar orbiting SSM/I and ERS satellite platforms, and cloud drift
winds derived from tracking low level visible cloud imagery from
geostationary satellites. These data are composited relative to the
storm over a 4-6 hour period. All data are quality controlled and
processed to conform to a common framework for height (10 m or 33
feet), exposure (marine or open terrain over land), and averaging
period (maximum sustained 1 minute wind speed) using accepted methods
from micrometeorology and wind engineering (Powell et al., 1996,
Powell and Houston, 1996). This framework is consistent with that
used by the National Hurricane Center (NHC), and is readily converted
to wind load frameworks used in building codes.
Further details on the HRD wind analysis methods may be found in the
papers listed below.
Burpee, R. W., S. D. Aberson, P. G. Black, M. DeMaria, J. L. Franklin, J.
S. Griffin, S. H. Houston, J. Kaplan, S. J. Lord, F. D. Marks, Jr., M. D.
Powell, and H. E. Willoughby, 1994: Real-time guidance provided by NOAA's
Hurricane Research Division to forecasters during Emily of 1993. Bull.
Amer. Meteor. Soc., 75, 1765-1783.
Powell, M. D. , P. P. Dodge, and M. L. Black, 1991: The landfall of
Hurricane Hugo in the Carolinas. Weather Forecast., 6, 379-399.
Powell, M. D., S. H. Houston, and I. Ares, 1995: Real-time damage
assessment in hurricanes. 21st AMS Conference on hurricanes and tropical
meteorology, Miami, FL., April 24-28, 1995, p 500-502.
Powell, M. D., S. H.Houston, and T. A. Reinhold, 1996: Hurricane
Andrew's Landfall in South Florida. Part I: Standardizing
measurements for documentation of surface wind fields. Weather
Forecast., 11, 304-328.
Powell, M. D., and S. H. Houston, 1996: Hurricane Andrew's Landfall
in South Florida. Part II: Surface Wind Fields and Potential
Real-time Applications. Weather. Forecast., 11, 329-349.
Powell, M. D., S. H. Houston, L. R. Amat, N. Morisseau-Leroy, 1998:
The HRD real-time hurricane wind analysis system. J. Wind
Engineer. Ind. Aerody., 77&78, 53-64.
Powell, M. D., and S. H. Houston, 1998: Surface wind fields of 1995
Hurricanes Erin, Opal, Luis, Marilyn, and Roxanne at landfall. Mon
Wea. Rev., 126, 1259-1273.
Powell, M. D., and S. H. Houston, 1999: Comments on "A Multiscale
Numerical Study of Hurricane Andrew (1992). Part I: Explicit
Simulation and Verification". Mon. Wea. Rev., 127, 1706-1710.