Numerical model experiments are conducted to address the previously unexplained anomalously high storm surge along the Florida coast of Apalachee Bay during Hurricane Dennis (2005). The 2--3 m surge observed during this storm cannot be obviously explained by the relatively weak local winds over this bay 275 km east of the storm center. Realistic and idealized numerical experiments demonstrate that the along-shore winds to the east of the storm center built a high sea level anomaly along the coast which traveled northward to Apalachee Bay as a topographic Rossby wave. The wave was amplified as the storm moved nearly parallel to the shelf and at comparable speed to the wave phase speed. These results suggest that enlarging the domain of the storm surge forecasting models can improve the surge forecast for a storm moving along a similar track, and have now been applied to operational use.