Case Study of Erin Using the FSU Nested Regional Spectral Model

Abstract

A case study of Hurricane Erin of the 1995 storm season is presented using the recently developed Florida State University (FSU) Nested Regional Spectral Model. The nested regional spectral model uses a perturbation technique similar to that used in the National Centers for Environmental Prediction and European Centre for Medium-Range Weather Forecasts regional spectral models, but with a number of differences such as the use of a Mercator projection. The perturbations are deviations from the FSU Global Spectral Model (FSUGSM) results and are spectrally represented with π-periodic trigonometric basis functions. The perturbations are relaxed at the boundary to approach the global model results. The perturbation time tendencies are solved using a semi-implicit time integration scheme similar to that used in the FSUGSM. The regional model has the same sigma-coordinate vertical structure and physics as the FSUGSM. Implicit horizontal diffusion and time filtering of the perturbations is included. Erin made landfall on both the Atlantic coast and gulf coast of Florida, each time with hurricane strength. A 4-day prediction is performed using a 0.5° transform grid, which yields an equivalent resolution to a T240 global model. T106 and T126 global models were used to provide base fields for the regional model as well as control experiments. The intensity forecast of the regional model was superior to that of the global model and reasonably close to the observed intensity. With physical initialization, the forecast track of the storm is improved in both the global and regional models. However, the regional model predicted the best track, showing both landfalls within 100 km of the observed landfalls.