Actually, publicly revealing when, how and where the United States (and some allies) will likely strike makes sense, given what Obama wants to accomplish. If his goal were to fully enter the Syrian civil war and decisively end it, then, yes, secrecy would be the way to go. But the administration has been very clear that it has a much more modest goal: to punish Syrian leader Bashar al-Assad for his suspected use of chemical weapons so that he, and future military leaders, won't do it again.
What's about to happen, if the United States and allies do go through with the strikes, is less of a war and more of a ritual. This isn't about defeating Assad, it's about punishing him. And that calls for being really precise about how much punishment the United States imposes.
If the U.S. military just fired off a bunch of missiles, it would probably cause more civilian causalities than with its current approach, and the amount of damage it caused would be tougher to predict. Maybe it causes less damage than the United States wants, and then Assad is not sufficiently deterred from future chemical weapons use. Maybe it causes more damage, and then Assad might feel compelled to respond, perhaps by striking Israel, and that's how things spiral out of control.
No, what the Obama administration appears to want is a limited, finite series of strikes that will be carefully calibrated to send a message and cause the just-right amount of pain. It wants to set Assad back but it doesn't want to cause death and mayhem. So the most likely option is probably to destroy a bunch of government or military infrastructure -- much of which will probably be empty.
This is what the Clinton administration did in 1998 with Operation Desert Fox, when it and the United Kingdom bombed Iraq as punishment for cheating on weapons of mass destruction disarmament. The strikes were also intended to degrade Iraq's WMD production capacity. The 100 or so targets were, as now with Syria, telegraphed ahead of time. Many of them were empty. Iraq knew it was coming and was mostly unsurprised, which meant that it didn't escalate. The campaign was limited in scope and, although the history of Iraq and WMDs is obviously a thorny one, appeared to be largely successful at least at punishing Saddam Hussein.
President Obama has long made clear that he worries that any involvement in Syria could lead the United States to get sucked into a long and intractable conflict that it would hurt more than help. But his administration also clearly believes that Assad's suspected chemical weapons use could set a potentially dangerous enough precedent that it demands some military response. A Desert Fox-style limited, telegraphed, calibrated series of offshore strikes appears to be the balance that the administration is striking.