The FIMP nearshore grid covered only the coast and bays of southern Long 
Island. 
189. The scarcity of historical water level records for southern Long 
Island required a synthetic modeling approach to generate the large number of 
independent events (water levels) needed for construction of stage-frequency 
curves. For hurricanes, the joint probability method (JPM) (Meyers 1970) was 
used to create synthetic storms. An individual hurricane can be represented 
by five parameters: central pressure deficit (DP), forward speed (FS), radius 
of maximum winds (RM), track angle (TA), and landfall point (LP). Probability 
was assigned to an individual storm by determining the probability of each 
parameter value in that storm. If the parameters are independent, the storm 
probability is the product of the probability of each component parameter. 
However, in the New York Bight, not all parameters were found to be indepen- 
dent. There were two "dependency limbs," one involving DP above and below 
2 in. Hg, and one involving bypassing storm tracks. A total ensemble of 
918 synthetic hurricanes was generated from all possible combinations of 
selected parameter values within each dependency limb as shown in Table 10. 
Table 10 
Construction of Synthetic Hurricane Ensemble 
for FIMP Study 
Parameter Combinations 
Dependency Limb DP RM FS TA LP Total 
Landfalling Storm Tracks 
High Pressure 2 3 3 3 5 270 
Low Pressure 4 3 3 3 5 540 
Bypassing Storm Tracks 6 3 3 2 1 108 
Total 918 
 ——  ———————————————————————————— 
190. Northeasters are more difficult to parameterize than are hurri- 
canes; therefore, historical data were used to establish a northeaster storm 
ensemble for FIMP. Twenty-seven storms were selected as representative of the 
41-year period of 1940 through 1980. Water level data, after the subtraction 
of predicted tide, were used to develop a partial duration stage-frequency 
curve of northeaster surge levels at Sandy Hook, New Jersey. Probabilities 
104 
