ON THE GULF OF MEXICO — Key ships stationed over BP's crippled well in the Gulf of Mexico were ordered to evacuate Thursday ahead of Tropical Storm Bonnie, and engineers have grown so confident in the leaky cap fixed to the well head that they will leave it closed while they are gone. Tropical Storm Bonnie, which blossomed over the Bahamas and was to enter the Gulf of Mexico by the weekend, could delay by another 12 days the push to plug the broken well for good using mud and cement, retired Coast Guard Adm. Thad Allen and BP officials conceded. Even if it's not a direct hit, the rough weather will push back efforts to kill the well by at least a week. "While this is not a hurricane, it's a storm that will have probably some significant impacts, we're taking appropriate cautions," Allen said in Mobile, Ala. Allen issued the order Thursday night to begin moving dozens of vessels from the spill site, including the rig that's drilling the relief tunnel engineers will use to permanently throttle the free-flowing crude near the bottom of the well. Some vessels could stay on site, he said. "While these actions may delay the effort to kill the well for several days, the safety of the individuals at the well site is our highest concern," he said in a statement. A week of steady measurements through cameras and other devices convinced Allen they don't need to open vents to relieve pressure on the cap, which engineers had worried might contribute to leaks underground and an even bigger blowout. The cap was attached a week ago, and only minor leaks have been detected. Allen said earlier in the day that evacuating the vessels could leave the well head unmonitored for up to a few days. He said he ordered BP to make sure that the ships carrying the robotic submarines watching the well are the last to leave and the first to return.