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Tropical Storm Bonnie is due to enter the Gulf of Mexico by the weekend, forcing cleanup ships to evacuate.
The storm could delay an operation to plug the broken well with mud and cement, for another 12 days. Even under the best scenario, the rough weather will block efforts to kill the well for at least a week.
US officials have ordered dozens of vessels to be moved from the spill site, including the drilling rig for the relief tunnel.
Scientists say the storm won't affect the well cap, which is 1.6 kilometers beneath the ocean surface.