Associated Press

MIAMI -- A tropical depression racing toward the Gulf of Mexico Thursday increased pressure on BP and the U.S. government to decide whether to evacuate dozens of ships at the site of the ruptured oil well.

The National Hurricane Center in Miami said a cluster of thunderstorms in the Bahamas formed into a tropical depression Thursday morning. It could reach the spill site within two and a half days, said Lexion Avila, a senior hurricane specialist.

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Seas already were choppy in the Gulf, with waves up to five feet rocking boats as crews waited for orders on whether to leave. Nonessential vessels like barges and skimmers will likely be sent back to shore, Commander Terri Jordan told the crew of the Coast Guard cutter Decisive at a midmorning briefing.

She said they were awaiting an evacuation order for key vessels.

Work on plugging the well is at a standstill just days before the expected completion of a relief tunnel to permanently throttle the free-flowing crude.

Worse yet, the government's spill chief said foul weather could require reopening the cap that has contained the oil for nearly a week, allowing oil to gush into the sea again for days while engineers wait out the storm.

"This is necessarily going to be a judgment call," said retired Coast Guard Adm. Thad Allen, who was waiting to see how the storm developed before deciding whether to order any of the ships to leave.

BP spokesman Scott Dean said Thursday morning that no decisions had been made yet.

Crews had planned to spend Wednesday and Thursday reinforcing with cement the last few feet of the relief tunnel that will be used to pump mud into the gusher and kill it once and for all. But BP put the task on hold and instead placed a temporary plug called a storm packer deep inside the tunnel, in case it has to be abandoned until the storm passes.

"What we didn't want to do is be in the middle of an operation and potentially put the relief well at some risk," BP vice president Kent Wells said.

If the work crews are evacuated, it could be two weeks before they can resume the effort to kill the well. That would upset BP's timetable, which called for finishing the relief tunnel by the end of July and plugging the blown-out well by early August.

Scientists have been scrutinizing underwater video and pressure data for days, trying to determine if the capped well is holding tight or in danger of rupturing and causing an even bigger disaster. If the storm prevents BP from monitoring the well, the cap may simply be reopened, allowing oil to spill into the water, Allen said.

BP and government scientists were meeting to discuss whether the cap could be monitored from shore.

As the storm drew closer, boat captains hired by BP for skimming duty were sent home and told they wouldn't be going back out for five or six days, said Tom Ard, president of the Orange Beach Fishing Association in Alabama.

In Florida, crews removed booms intended to protect waterways in the Panhandle from oil. High winds and storm surge could carry the booms into sensitive wetlands.

Also, Shell Oil began evacuating empman for Transocean, the owner of the rig leased by BP, confirmed the existence of the reports to The Associated Press.

"As part of Transocean's unwavering commitment to safety and rigorous maintenance discipline on all our rigs, we proactively commissioned the safety survey and the rig assessment review," Transocean spokesman Lou Colasuonno said in an e-mail early Thursday. "A fair reading of those detailed third-party reviews indicates clearly that while certain areas could be enhanced, overall rig maintenance met or exceeded regulatory and industry standards and the Deepwater Horizon's safety management was strong and a culture of safety was robust on board the rig."