NEW ORLEANS, Louisiana (AFP) – A tropical storm barreled toward the Gulf of Mexico Friday, forcing the evacuation of crews working on the huge oil spill and prolonging the region's environmental and economic nightmare.

The cap in place for a week on the ruptured well will remain in place, but efforts to complete the relief wells for a permanent fix were set back by the evacuation ordered as Tropical Storm Bonnie churned toward the area.

At 11:00 pm (0300 GMT Friday) the storm was between the Bahamas and the Florida Keys, moving northwest at 19 kilometers (12 miles) per hour, the National Weather Service said.

Warnings were posted for Florida coastal areas and the storm track appeared headed toward Louisiana and the vast area affected by the oil spill.

"Due to the risk that Tropical Storm Bonnie poses to the safety of the nearly 2,000 people responding to the BP oil spill at the well site, many of the vessels and rigs will be preparing to move out of harm's way beginning tonight," US response chief Admiral Thad Allen announced.

"This includes the rig drilling the relief well that will ultimately kill the well, as well as other vessels needed for containment. Some of the vessels may be able to remain on site, but we will err on the side of safety."

Officials have said the evacuation of the drilling rig will lead to a delay of up to 12 days in the final operation to plug BP's runaway well, but Allen sought to play down those concerns.

"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.

Allen decided the cap holding back the torrent of crude for the past week would stay on, providing some respite for those in the Gulf region struggling to cope with the huge economic impact of the disaster.

There had been fears the cap would have to be opened up or even removed because nobody would be on site to monitor any pressure anomalies in the well or oil seepage on the sea floor.

But Allen said he had ordered BP to make sure their remotely operated vehicles (ROV's) which do the crucial monitoring for oil leaks and other anomalies are the last to leave when the storm arrives.

Latest forecasts show the storm hitting the area on Saturday morning and likely to pass by early Sunday.

Crucial work to concrete in the casing on the relief well will now be postponed until the giant drilling rig can return.

After that sets, a process expected to take up to a week, officials hope to perform a "static kill" to plug the well by injecting heavy drilling mud and cement through the cap at the top.

The final operation to cement the reservoir once and for all through the relief well would be expected five to seven days after that.

The evacuation was a huge blow for local residents who already see efforts to choke off the well as too little too late, with hundreds of miles of coastline already fouled.

The five US states along the Gulf of Mexico could lose 22.7 billion dollars in tourist revenue over the next three years because of the spill, a study showed Thursday.

A vast swath of the Gulf has also been closed to commercial and sport fishing since the BP-leased Deepwater Horizon rig sank on April 22, two days after an explosion that killed 11 workers.

But US officials reopened Thursday one third of those fishing grounds after no oil was seen in the area for 30 days and tests revealed the fish there were not being polluted.

Oil industry jobs in the region were also hit by President Barack Obama's decision to impose a moratorium on new deepsea drilling -- a move fiercely opposed by local leaders.

If an upper estimate of over four million barrels is confirmed, what is considered one of America's worst ever environmental disasters would also be the biggest accidental oil spill ever.

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