3. Tide gauge data 



A total of 9 and 13 tide gauge stations for hurricane Car la and 

 Allen, respectively, were chosen to provide the observed response in 

 the Gulf of Mexico. Figure 12 shows locations of these tide gauge 

 stations. The Tides Prediction Branch of the National Oceanic and 

 Atmospheric Administration (NOAA) and the National Autonomous 

 University of Mexico (UNAM) provided hourly water level for a period 

 of several weeks before and after the hurricanes. Filtered versions 

 (using a 40 h lowpass filter) are shown in Figs. 13-15 for some 

 selected series obtained during hurricane Car la. These filtered 

 plots essentially remove the tides. The arrows in the figures 

 indicate the time at which the center of Carla entered the Gulf 

 through Yucatan Strait. There were indications of a gradual rise of 

 water level well before the peak surge, a possibility of forerunner 

 surges at all 9 stations. Note also the degree of background 

 variation unrelated to the hurricane several weeks prior to the 

 hurricane. 



The same analysis as applied to recorded water level for 

 hurricane Carla were used for the records obtained obtained during 

 hurricane Allen. Figures 16-18 show the filtered data at some 

 selected stations. The presence of an initial rise in water level is 

 again observed at all stations. 



The lowpass filtering illustrated above is known to smooth out 

 and broaden the peak surge. To properly remove tidal signals from 

 recorded data by the harmonic method requires a suitable number of 

 constituents to insure proper phasing. Unfortunately, only the Key 



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