New Orleans ? BP’s effort to drill a relief well through 2 1/2 miles of rock to stop the Gulf spill is on target for completion by mid-August, the oil giant said Friday. But BP’s stock tumbled anyway over the mounting costs of the disaster and the company’s inability to plug the leak sooner.

The first tropical depression of the Atlantic season formed in the Caribbean, raising concerns about what might happen to efforts to contain the oil if bad weather forces BP to abandon them. It’s still too early to tell exactly where the storm might go and how it might affect oil on and below the surface of the Gulf.

The relief well is considered the best hope of halting the crude that has been gushing since April 20 in the biggest offshore oil spill in U.S. history.

The crew that has been drilling the relief well since early May ran a test to confirm it is on the right path, using a tool that detects the magnetic field around the casing of the original, blown-out well.

“The layman’s translation is, ‘We are where we thought we were,”‘ said BP spokesman Bill Salvin.

Several such tests are necessary, since drilling sideways into the original well casing requires boring through more than 13,000 feet of rock to hit a target 9 inches in diameter, or about the size of a dinner plate.

Once the new well intersects the ruptured one, BP plans to pump heavy drilling mud in to stop the oil flow and plug it with cement.

Despite the encouraging news, BP stock tumbled 6 percent in New York on Friday to a 14-year low on news that BP has now spent $2.35 billion dealing with the disaster.

BP has lost more than $100 billion in market value since its deep-water drilling platform blew up, and its stock is worth less than half the $60 or so it was selling for on the day of the explosion.

Meanwhile, forecasters and the oil company kept an eye on the tropical depression with winds up to 35 mph churning in the Atlantic. Forecasters predicted it would strengthen into a tropical storm and reach Mexico’s Yucatan Peninsula by Saturday night.

Michael Brennan, a hurricane specialist at the National Hurricane Center in Miami, said it’s too early to tell if the storm will affect the northeastern part of the Gulf, where the spill is.

Most models show it traveling over the Yucatan Peninsula this weekend and heading back into the southern part of the Gulf by Monday. After that, some models have it heading toward the spill while others do not.

The effort to capture the oil gushing from the sea bottom could be interrupted for up to two weeks if a storm forces BP to move its equipment out of harm’s way, said Coast Guard Adm. Thad Allen, the government’s point man on the crisis.

In other news:

l A financial disclosure report released Friday shows that the Louisiana judge who struck down the Obama administration’s six-month ban on deep-water drilling in the Gulf has sold many of his energy investments. U.S. District Judge Martin Feldman still owns eight energy-related investments, including stock in Exxon Mobil Corp. Among the assets he sold was stock in Transocean, which owned the rig that exploded. The Justice Department asked a federal appeals court Friday to delay Feldman’s ruling “to preserve the status quo” during the government’s appeal.

l Labor Secretary Hilda Solis slammed BP — along with Massey Energy, owner of the West Virginia coal mine where 29 workers died in an explosion in April — saying they need better safety measures. “We are not saying go out of business,” she said. “Do your job better. Make an investment in your employees. We want you to make a profit, but not at the expense of killing your employees.”

l Vice President Joe Biden will head to the Gulf on Tuesday to visit a command center in New Orleans and the oil-fouled Florida Panhandle.

l The IRS said payments for lost wages from BP’s $20 billion victims compensation fund are taxable just like regular income. Payments for physical injuries or property loss are generally tax-free.

BP is drilling two relief wells, in case the first one misses its mark. The first one, started May 2, reached a depth of 16,275 feet Wednesday — including about 5,000 feet of water — before workers paused for the test.