Rain storms moving toward the Gulf of Mexico Wednesday threatened to shut down undersea efforts to seal BP's ruptured well, interrupting work just as engineers get close to plugging the leak with mud and cement.
Retired U.S. Coast Guard Adm. Thad Allen said tropical weather could force crews on the water to abandon their watch over the experimental cap that's been bottling oil a mile below the surface of the water for nearly a week.
Scientists have been closely watching to determine if the cap is displacing pressure and causing leaks underground. If they can't observe the cap because of bad weather -- for up to four days, Allen said -- they could decide to reopen the cap to avoid missing signs the well is buckling.
Forecasters say the storm system will likely move into the Gulf of Mexico over the weekend, although it appears to be weakening. Right now, it has a 60 percent chance of becoming a tropical depression or storm within the next 48 hours.
In Florida, crews were removing protective boom intended to buffer the state's inland waterways in the Panhandle from oil. High winds and storm surge could carry the boom into sensitive wetlands, damaging those areas.
Allen said BP and government scientists were meeting to discuss whether the cap could be monitored from the shore.
"This is necessarily going to be a judgment call," Allen said.
It could take several days to evacuate ships from the well site 50 miles off the Louisiana coast, where the BP-leased Deepwater Horizon rig exploded April 20, killing 11 and touching off one of America's worst environmental crises. Shell already has begun evacuating personnel not essential to producing and drilling on their operations in the Gulf.
Allen said an evacuation could delay operations as much as two weeks before work would resume to kill the well at the bottom.
Crews are in the final stages of readying a relief tunnel before boring into the side of the ruptured well to dump heavy mud and cement, sealing it for good. BP also may pump mud and cement from the top, to make efforts at the bottom easier. That procedure, called a surface kill, would occur before the well is ultimately plugged from below.
Before talk of nasty weather, BP was inching closer to completion and had aimed for early August for the plug.
The well has spewed somewhere between 94 million and 184 million gallons into the Gulf. BP said the cost of dealing with the spill has now reached nearly $4 billion.
Associated Press writers Jay Reeves in Orange Beach, Ala., Janet McConnaughey and Phuong Le in New Orleans, Michael Kunzelman in Kenner, La., Ben Feller and Frederic J. Frommer in Washington and Robert Barr in London contributed to this report, along with AP energy writer Chris Kahn in New York.