Ivan became 2004's strongest Atlantic Basin hurricane Thursday, joining the limited ranks of tropical storms which have reached "Cat. 5" intensity. Category 5 storms are so designated when sustained winds reach 155 m.p.h. While Ivan will fluctuate between Cat. 4 and 5 strength in coming days, the monstrous storm is threatening a devastating rendezvous with Jamaica. Computer models are nearly unanimous that the island may sustain a direct hit later Friday. Hurricanes of Ivan's strength are capable of demolishing buildings and literally pulling trees from the ground. So strong are Ivan's winds that within its 60 mile core, it features winds with velocities equal to an F2 or F3 tornado--and that's taking place over an area equivalent to the distance from Chicago to DeKalb. Unlike torandoes, which hit quickly then retreat, the winds of a hurricane last for hours. The storm next crashes into Cuba, which may temporarily sap some of its strength. But its reemergence over the warm Gulf of Mexico threatens intensification, most likely to at least a Category 2 or 3 storm (winds 96+ m.p.h.) as it approaches Florida Monday.