P is the central pressure, and Pj^ is the ambient pressure. 



Holland determined C and k by fitting the pressure profile 



P = Pj, + (Pji - Pc)exp(-C/r^). (69) 



However, he pointed out that this approach would underestimate the 



peak winds and that wind observations, if available, should be used 



directly. 



For hurricane Carla, there were detailed surface charts 



available. Equation (68) was modified for the direct approach as 



follows: First, C was eliminated by considering that the 



cyclostrophic wind 



1 

 W^ = [Ck(Pn - Pc)exp(-C/r^)/Par^]2, (70) 



was a more appropriate representation of the maximum wind. Upon 

 taking dWj,/dr and setting it equal to zero at r=R, we obtain the 

 relation 



R = C^/^ or C = R^ . (71) 



Since detailed surface charts allow a good estimate of the maximum 



wind and radius of maximum wind, the pressure drop (Pj^-P^,) was 



represented in terms of the maximum wind by substituting (71) in (70) 



to obtain 



1 

 Wm = [(k/Pae)(Pn " Pc^^^' (72) 



Using (71) and (72), (68) reduces to 



1 

 W = [(R/r)^w2exp(l-(R/r)^) +(Jrf)2]2 - Jrf . (73) 



35 



