showed no significant departure from the expected tide during passage of the 
storm. This was not unexpected as these gages were on the backside of the 
storm about 70 miles from the point of closest approach. 
17. The CERC gage T-14 functioned until about 0300 CDT 18 August when 
it failed. The cause of the failure was determined to be a defective pressure 
case which allowed water into the electronic circuits. Reduction and correc- 
tion of the available data from T-14 is discussed in the following section. 
Correction of Absolute Pressure Tide Recorders 
18. Use of an uncompensated pressure-measuring sensor such as that 
employed in this program requires the data to be compensated for changes in 
atmospheric pressure during passage of the storm. A change of 1 in. of 
mercury in atmospheric pressure is approximately equivalent to a change of 
1 ft in water level. Changes in atmospheric pressure of 2 in. of mercury 
are common during passage of a storm; consequently, it is essential that such 
changes be taken into account when computing a hydrograph from uncompensated 
pressure data. 
19. The simplest and most accurate means of compensating the pressure 
record would be to place a barograph near the tide gage; however, this is 
seldom feasible from both logistic and economic standpoints. An alternative = 
method is by means of an analytic model to interpolate in time and space using 
data observed elsewhere in the affected area. There are a number of models 
to choose from, some developed from theoretical considerations, others by 
empirical best fit to the smoothed pressure profiles of several hurricanes. 
20. The model found to give the best fit to the observed data for 
Alicia is 
P - Po 
es ie 
BoeeaP ae C (arc tangent 2 ) 
fo) 
where 
P = pressure to be computed 
Po = central pressure of storm 
Po = far field pressure 
C = constant (set to 0.6 for Alicia) 
r = distance from storm center at which pressure is to be computed 
Yr = radius to maximum winds 
12 
