Sad to say, the warning time that the residents of Sumatra had before the 2004 tsunami hit land was close from little to none. A rough estimation would around 15 - 30 minutes. They say that the primary cause would be that there wasn't any warning systems over the Indian Ocean at that time. Another thing, which is what most people who knew about it would point out as the real problem, is that there was no issuance of a warning in the first place. The quake was detected an hour or so before the tsunami occurred in the Pacific Tsunami Warning Centre located in Ewo, Hawaii. At that moment, the information was relayed to Australia and to the rest of the world. The question wasn't why the Centre didn't issue a warning, but why the whole world network of information didn't issue one. They say that other sophisticated data were available at that time and almost immediately since the tsunami was active.
