Deadly hurricane Ivan threatens to crash into the Gulf Coast near Mobile Bay Wednesday night as the most powerful tropical cyclone to sweep that area in a quarter century. The last time a hurricane bearing winds as strong hit was in 1979 when Frederic roared ashore at roughly the same point on the Gulf Coast. A northbound trip up the west end of Mobile Bay, a path considered plausible by forecasters at the National Hurricane Center, could prove devastating in terms of the "storm surge". Storm surges occur when prolonged onshore winds and the storm's extremely low central air pressure pile water up against the shore. The path projected for Ivan brings the storm ashore Wednesday night and moves it north paralleling Mobile Bay's western shoreline exposing the full length of the relatively confined channel to hours of powerful winds, forcing water levels to rise. Hurricanes of Category 4 intensity (131-155 m.p.h. sustained winds) are capable of generating devasting level increases of 12 to18 ft. in the most extreme cases.