Subject: RECONSTRUCTION OF SURFACE WIND FIELDS FOR TROPICAL CYCLONES AFFECTING FLORIDA BAY

Principal Investigator(s):
Samuel H. Houston
Dr. Mark D. Powell
Collaborating scientist(s):
Dr. George A. Soukup (NOAA/AOML/HRD)
Ms. Summer C. Spisak (NOAA/AOML/HRD)
Mr. Luis. Amat (NOAA/AOML/HRD)

Objective: The primary objective of this research project is to reconstruct episodic/catastrophic meteorological events which critically affect the South Florida ecosystem.
Rationale: Tropical cyclones are believed to exert considerable influence on the health of Florida Bay. Wind fields associated with these storms generate surface stress and an associated response in the bay circulation patterns and sediment transport. Because the "multiple pond-bank" nature of Florida Bay inhibits sediment transport forced by relatively weak wind conditions, hurricanes are believed to play a critical role in removing or transporting sediment from the bay. Severe winds associated with tropical cyclones may also contribute to ecosystem health as a result of the post-storm decay of organic material damaged by the wind and storm surge. In order to assess the response of Florida Bay to episodic wind events, circulation and ecological modelers would benefit from wind field analyses based on reconstruction of past events.
Method: Gridded tropical cyclone surface wind fields are being generated from real case analyses and numerical model simulations to produce a catalog of datasets. Research scientists will be able to quickly retrieve data from this event/regime archive for use in circulation model simulations/predictions, hydrological modeling, natural systems restoration, and biological impact studies. We plan to analyze the most significant storms to affect Florida Bay over the past century. In so doing we will attempt to show a variety of wind field affects on Florida Bay which could comprise an archive of the types of extreme events that can be expected over the next century. Data will be processed to achieve a consistent framework in terms of averaging time, height and exposure. For storms with few data available the wind profile fit currently used in a planetary boundary layer model developed by Shapiro (1983) and implemented by Vickery and Twisdale (1995) will be adapted to construct a background field. These data will then be objectively analyzed using the Spectral Application of Finite-Element Representation (SAFER) method (Ooyama 1987, Franklin et al. 1993). This method uses cubic B-splines to minimize the difference between the input observations and the analysis. The methods used to standardize the input data for analysis are described in Powell et al. (1996) and Powell and Houston (1996, 1997). The scale of the analysis is controlled by the analyst depending on the features that need to be resolved. Snap shots of the streamline and isotach fields for each storm will be generated for a 4 x 4 degree lat-lon domain centered on Florida Bay at 6-12 h intervals, depending on the translation speed of the storm. This domain should also be suitable for those interested in studying extreme wind affects on the southern end of the Everglades. Images of the wind fields are archived on our World Wide Web (WWW) site (http://www.aoml.noaa.gov/hrd/Storm_pages/frame.html) for access by Florida Bay researchers and gridded fields will be generated upon request. These fields should be capable of import to geographical information systems for correlation studies with other geo-referenced fields such as mangroves, reefs, and turbidity plumes.
Accomplishment: In November of 1994, NOAA/AOML/HRD hosted the South Florida Atmospheric Modeling Workshop (NOAA, Nov. 1994), attended by 40 researchers representing meteorology, hydrology and physical oceanography from south Florida's research community. Attendees expressed the need for a catalog of meteorological events/regimes which critically affect the South Florida ecosystem. Gridded datasets from this archive could be accessed for circulation/ecological model simulations, hydrological modeling, natural systems restoration, and biological impact studies. Based on this need we reconstructed surface wind fields for tropical cyclones that affected Florida Bay. For example, the Labor Day Hurricane of 1935 (Figure 1), Hurricane Donna of 1960 (Figure 2) and Hurricane Betsy of 1965 (Figure 3) wind fields are now available. The tracks of these hurricanes through Florida Bay may have contributed to flushing the bay. As shown by the streamlines in Figures 1 and 2, the flow over the bay was dominated by east and northeast wind directions, which may have forced sediment to the southern portion of the bay as the Labor Day Hurricane of 1935 and Donna approached the area from the southeast. In addition, the strong winds in excess of hurricane force along the fringes of the bay damaged mangroves and other vegetation leading to decay of large amounts of organic material in the northern part of the bay. In contrast, the center of Hurricane Betsy (Fig. 3) moved nearly westward over the bay. This was a weaker hurricane than in 1935 or 1960, but it would have likely had a significant affect on the bay. Once gridded surface wind fields are available on our WWW site (http://www.aoml.noaa.gov/hrd/Storm_pages/frame.html), they will assist circulation modelers to determine how the bay responds to hurricanes.
Key references:

South Florida Atmospheric Modeling Workshop (NOAA, Nov. 1994)

Franklin, J. L., S. J. Lord, S. E. Feuer, and F. L. Marks, 1993: The kinematic structure of Hurricane Gloria (1985) determined from nested analyses of dropwindsonde and Doppler data. Mon. Wea. Rev., 121, 2433-2451.

Ooyama, K. V., 1987: Scale controlled objective analysis. Mon. Wea. Rev., 115, 2479-2506.

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 and Forecasting, 11, 304-328.

Powell, M. D., and S. Houston, 1996: Hurricane Andrew's Landfall in South Florida. Part II: Surface Wind Fields and Potential Real-time Applications. Weather and Forecasting, 11, 329-349.

Powell, M. D., and S. H. Houston, 1997: Surface wind fields of 1995 Hurricanes Erin, Opal, Luis, Marilyn, and Roxanne at landfall. Mon. Wea. Rev., (In press).

Shapiro, L. J., 1983: The assymmetric boundary layer flow under a translating hurricane. J. Atmos. Sci., 40, 1984-1998.

Vickery, P. J., and L. A. Twisdale, 1995: Wind field and filling models for hurricane wind speed predictions. J. Structural Engineering, ASCE, 121, 1700-1709.

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