An indication of the distribution of waves throughout a hurricane can 

 be obtained by plotting composite charts of shipboard wave observations. 

 The position of a report is determined by its distance from the storm 

 center and its direction from the storm track. Changes in storm intensity 

 and shape are often small enough to permit all observations obtained during 

 a period of 24 to 36 hours to be plotted on a single chart. Several plots 

 of this type from Pore (1957) are given in Figure 3-32. Additional data 

 of the same type have been presented by Arakawa and Suda (1953) , Pore (1957) 

 and Harris (1962) . 



Goodknight and Russell (1963) give a tabulation of the significant 

 height and period for waves recorded on an oil drilling platform in approxi- 

 mately 33 feet of water, 1.5 miles from shore near Burrwood, Louisiana 

 during hurricanes Audrey, 1957, and Ella, 1950, and tropical storms Bertha, 

 1957, and Esther, 1957. These wave records were used to evaluate the 

 applicability of the Rayleigh distribution function (Section 3.22. Wave 

 Height Variability) to hurricane statistics for wave heights and periods. 

 They concluded that the Rayleigh distribution function is adequate for 

 deriving the ratios between Hg, Hio, H, etc., with sufficient accuracy 

 for engineering design, but that its acceptance as a basic law for wave 

 height distributions is questionable. 



3.72 MODEL WIND AND PRESSURE FIELDS FOR HURRICANES 



Many mathematical models have been proposed, for use in studying 

 hurricanes. Each is designed to simulate some aspect of the storm as 

 accurately as possible without making excessively large errors in describ- 

 ing other aspects of the storm. Each model leads to a slightly different 

 specification of the surface wind field. Available wind data are suffi- 

 cient to show that some models duplicate certain aspects of the wind field 

 better than certain other models; but there are not enough data for a 

 determination of a best model for all purposes. 



One of the simplest and earliest models for the hurricane wind field 

 is the Rankin vortex. For this model, it is assumed that 



U = Kr for r < R , 



KR^ (3-27) 



U = for r > R , 



r 



where K is a constant, R is the radial distance from the storm center 

 to the region of maximum wind speed, and r is the radial distance from 

 the storm center to any specified point in the storm system. 



This model can be improved by adding a translational component to 

 account for storm movement and a term producing cross-isobar flow toward 

 the storm center. 



Extensions of this model are still being used in some engineering 

 studies (Collins and Viehman, 1971). This model gives an artificial 

 discontinuity in the horizontal gradient of the wind speed at the radius 

 of maximum winds, and does not reproduce the well-known area of calm 

 winds near the storm center. 



3-54 



