Semi-enclosed bays and estuaries are usually protected from hurricane-generated storm surges. When a hurricane travels on the land side, however, it may induce high storm surges, strong currents and destratification in the water column. Real-time observations and numerical model prediction both show a slab-like sloshing in Chesapeake Bay when it was hit by Hurricane Isabel in September 2003. Strong southeasterly winds in the right front quadrant of the storm forced water in Chesapeake Bay to move northward as a single layer, producing high sea levels and flooding in the northern Bay region including Baltimore and Annapolis. Furthermore, the strong landward winds erased water-column stratification and caused a strong intrusion of high-salinity shelf water into the Bay. After Isabel's passage, the longitudinal salinity gradient produces restratification and two-layer circulation in the Bay.