Development Of Non-Uniform Grid Storm Surge Model Applicable For Operational Use

Prisco D. Nilo

A two-dimensional storm surge model with non-uniform grid system is developed and used to simulate four local storm surge occurrences and one well documented storm surge event in South Carolina, USA. The hydrodynamic equations are vertically integrated and the model considers the effects of surface stress, gradient in atmospheric and water pressure, bottom stress and coriolis acceleration. A Rankine-vortex typhoon model is used to generate the cyclonic wind field. In the computation of surface stress the bulk-aerodynamic parameterization is utilized. While the bottom stress is assumed to vary directly with the depth-averaged current and inversely with the depth of the fluid. The model also have provision for overland flooding and coastal drying. The movement of the coastal boundary is governed by the difference between the surge height and the elevation of the adjacent grid inland. A number of theoretical experiments are conducted to test the response of the model to changes in grid resolution and basin characteristics. Results show that the model is sensitive to grid resolution and that storm surge predominantly occurs in shallow continental shelves. It is also shown that bay-shaped basins attain higher surges compared to straight coastlines. Further, it is shown that inland slope controls the extent of inland flooding. Actual simulations were performed which include the 1912 storm surge in Sogod Bay, the 1975 storm surge in Tandag, the 1981 storm surge in Baler Bay, the 1994 case of Katring which generated an insignificant surge height in Lamon Bay, and the 1989 storm surge in South Carolina. The results of the simulations demonstrate that the model has shown modest skill to simulate the depth-averaged current driven by the intense tangential winds of typhoons and to predict reasonable surge heights. An operational procedure for storm surge forecasting is also presented in this study for future consideration.

Estimating Tropical Cyclone Intensity Over Philippine Region Using NOAA TOVS Microwave Data And Surface Observations

Herman L. Ngohayon

Upper tropospheric temperature anomalies (T250) and the horizontal Laplacian to the upper tropospheric temperature field (2T250) were determined from the radiances remotely sensed by the TIROS Operational Vertical Sounder (TOVS) on board a NOAA series (11 and 12) of polar orbiting satellite. A total of 88 cases from 18 tropical cyclones passing over the Philippine Region were monitored and surface pressure anomalies at 6-and 12-degree radius (P6 and P12) and maximum surface wind speed (Vmax) were obtained. Relating these data, a statistical model was developed to estimate the tropical cyclone intensity. Results showed excellent correlation with about 80% of the variations in Vmax was accounted for by T. No significant improvement in the coefficient of determination (r²) was achieved when ²T was regressed in linear form, exponentially and when both T and ²T were combined as predictors. The same trend is observed in the predictive equations for the pressure anomalies P6 and   P12. The dependent samples indicate standard errors of 10 kts and 8 hPa for maximum winds and surface pressure, respectively, which is comparable with the results obtained by Le Marshall et al. (1994) and Velden et al. (1991) for Western North Pacific tropical cyclones. The accuracy of the intensity estimates suggest that this method could be adopted operationally to supplement the Dvorak method of intensity estimation.