3 Storm Data 



Event Definition 



To extract storm data from the larger working data set, a definition of what 

 is meant by a storm is necessary. For the purposes of this report, a storm is 

 defined using the characteristic wave height H ino and the length of time it 

 exceeds a certain level. To isolate the largest events, it was required that H^ 

 exceed 2 m for times at least 24 hr apart, and not drop below 1 m in the 

 interim. Wave conditions are normally relatively quiescent just before a 

 storm, generally being low-amplitude, long-period swell from the southeast 

 quadrant. To ensure at least one prestorm condition, data for a given event 

 were extracted from the main database from the beginning of the day contain- 

 ing a prestorm condition to the end of the day during which H ino first drops 

 below 1 m. 



Figure 3 shows a time series of H^ from the directional gauge for all col- 

 lections in the main database. Storm events that satisfy the above definition 

 are identified by letter or number. Their nominal durations are marked by 

 horizontal black bars. In all, 29 storm events were found and are referenced 

 by the letters A to Z and the numbers 1 to 3. Note that Event 3 follows 

 Event E. 



Table 1 lists the storm events shown in Figure 3, along with the start and 

 end dates defined by the criteria described above. Also shown are the maxi- 

 mum H^ observed during the storm and a nominal duration, defined as the 

 time elapsed from the first time H^ exceeds 2 m to the last time it drops 

 below 2 m. Linear interpolation between measured H^ was used to obtain 

 the exceedence times. Based on the definition of a storm described above, all 

 durations should exceed 24 hr. Several do not, which illustrates the pitfalls of 

 searching a 6,762-point database by eye. The shorter storms are retained here 

 because they do not differ from the longer storms except by their durations. 



Climatological Parameters 



Several characterizing parameters are used in this report to describe a 

 storm evolution. These parameters are given names and symbols common to 



10 



Chapter 3 Storm Data 



