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 cycle.

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, including the Step Frequency Microwave Radiometer measurements of surface winds, as well as U.S. Air Force Reserves (AFRES) C-130 reconnaissance aircraft, remotely sensed winds from the polar orbiting SSM/I and ERS, the QuikScat platform and TRMM microwave imager satellites, and GOES cloud drift winds derive from tracking low level near-infrared cloud imagery from these 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.

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REFERENCES:

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.

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