CONCLUSIVE EVIDENCE THAT A TROPICAL STORM'S SAFFIR-SIMPSON RATING HAS NO BEARING ON STORM SURGE HEIGHT: THE NATIONAL STORM SURGE DATABASE

The Program for the Study of Developed Shorelines (PSDS) at Western Carolina University (WCU) is using relational tools and geographic information systems (ArcGIS) to build a national storm surge database. The national database currently contains over 5800 storm surge data points from 42 hurricanes. Access to high-quality storm surge data is critical for calibrating and verifying models like ADCIRC and SLOSH, which are currently used to predict storm surge heights for a variety of different uses. Both a user-friendly website and mobile application are also being developed from the database.

Analysis of the database was performed to examine the relationship between storm surge and a variety of storm characteristics. Results show no significant relationship (R² = 0.02) between surge height and the widely used Saffir-Simpson scale, which is based solely on wind speed. In fact, of all the storm track characteristic data analyzed (landfall wind speed, landfall pressure, landfall diameter, track speed, track straightness and angle of impact), only pressure at landfall had a significant relationship with surge height, indicating that multiple factors likely control surge heights during a storm. Linear regression analysis shows a negative relationship between maximum surge and pressure with an R² of 0.6.

Five storms that have affected the Gulf of Mexico coastline have recorded surge measurements over 6 m, while only one storm (Hugo) has recorded surge over 6 m. Results of t-test analysis between east and gulf coast surge values for Category 3 hurricanes show a significant difference (p= 1.87 x 10^-5) between these two populations of values.

It is clear from this analysis that multiple factors likely control storm surge heights during a storm, including storm track and geomorphologic features. This suggests that the Saffir-Simpson scale should not be used to predict surge heights or to communicate these surge threats to the public. Any misunderstanding that a lower category storm (i.e., Katrina, which made landfall as a Saffir Simpson Scale category 3) is not as “dangerous” as a higher category storm could have disastrous and deadly consequences.