[Fred Schmude, manager of our StormWatch division and our resident geological expert, updates the Sumatra quake/tsunami situation.] Data received from local authorities on Sumatra indicate a local tsunami did strike some of the coastal islands off the west coast of Sumatra in the Indian Ocean. These islands are oriented from northwest to southeast and are exposed on the west side to waves associated with tsunamis (see map below).
Note the farther southern island in that chain is Kepulauan Mentawai located only about 30-40 km (18-24 miles) away from the epicenter, making it a possible candidate for a local tsunami. Also, data from the USGS (United States Geological Survey) did increase the magnitude of the quake from 7.5 to 7.7 meaning the likelihood of a least a local tsunami would have increased as well. Based on early reports, it appear a local tsunami did occur on the west sides of these coastal islands (see black circled region above) with an estimated height of anywhere between 10 and 20 feet especially on the southernmost island. Since the wave struck late at night there would have been little if any warning to evacuate the area. Already there are reports of at least 40 people killed and hundreds missing, centered on the west and south side of this island chain. A tsunami watch was issued for that area shortly after the quake, but quickly cancelled after about 1 to 2 hours once it was obvious that any quake-generated tsunami was local at best.