The rock is roughly 10 feet (3 meters) across, and it's expected to enter the atmosphere above northern Sudan at about 8 miles (12 km) per second. The energy released should be approximately equal to one kiloton of conventional explosives. Fortunately, no damage is expected, since the blast will take place in the upper atmosphere. Some fragments may fall to the ground, but the area is sparsely inhabited and they're unlikely to hit anyone.The first confirmation that the asteroid has exploded above Sudan comes from the crew of a KLM airliner. From Spaceweather:
The sight and sound, however, should be amazing — especially since the sky will still be dark when this meteor hits. The fireball may be visible over much of northern Africa, the Middle East, and possibly even southern Europe.
"Half an hour before the predicted impact-time of asteroid 2008 TC3, I informed an official of Air-France-KLM at Amsterdam airport about the possibility that crews of their airliners in the vicinity of the predicted impact would have a chance to see a fireball. And it was a success! I have received confirmation that a KLM airliner, roughly 750 nautical miles southwest of the predicted atmospheric impact position, has observed a short flash just before the expected impact time 0246 UTC. Because of the distance it was not a very large phenomenon, but still a confirmation that some bright meteor has been seen in the predicted direction.
Update: Watch JPL's Donald Yeomans as he explains the discovery of the asteroid here.