The stories of the flood from around the world speak of a flood that was unlike any other that had been experienced. And it was combined with ‘rain for forty days and forty nights’, not as a cause of the flood but after the flood.
The physical evidence on the earth also speaks to an extreme event. Velikovsky in Earth in Upheaval documents jumbled masses of broken bones found in rock clefts high above Western shores of Europe. The Alaskan mud deposits, again of jumbled masses of broken bones mixed with trees speak of violent tsunamis hitting the Western shores of America.
Both the stories and the physical evidence suggest massive flooding from the Sea hitting initially Western shores. The missing bit of the puzzle is what could cause the oceans to slosh around in such a fashion.
If earth crust displacement was underway when the asteroid impact of 12800 years ago happened, this could be the cause. Earth crust displacement could start and accelerate so slowly that the fluid oceans could be moved with the crust without any noticeable sloshing around. But if a sizeable asteroid hit the already moving crust, in the direction it was already travelling, this would cause an acceleration. You can do a back of the envelope calculation on this, as I have done in the appendix of my book. Estimate the mass of the asteroid and its speed and you can calculate its momentum. The force the asteroid applies to the crust is the rate of change of the momentum in the fraction of a second it would take to plough through the Laurentide ice sheet. Estimate the mass of the crust and apply Newton’s law that Force = mass x acceleration.
With some very reasonable estimates of a 6km radius comet, travelling at 35km/second, the acceleration imparted to the crust would be sufficient to move the crust 480 metres in 24 hours. This may not sound a lot but it could be sufficient. Though the crust would move, the seas would not. The gyroscopic effect of the rotation of the earth would keep them moving at their normal 1668km/hr rotation at the equator. Note also that the Atlantic and Pacific are narrower in the North than they are at the equator. If the crust moved South but the oceans stayed where they were, the oceans would indeed slosh over the land in huge tsunamis, worthy to be recorded in myths worldwide. This would be a truly worldwide flood, reflecting the fact that flood myths are found worldwide.
A possible alternative explanation could be a massive asteroid hitting an ocean, which might have happened at the end of the younger dryas period. However, though this could cause incredibly massive tsunamis, it is hard to imagine a strike in the Pacific causing huge floods in the Atlantic ocean, or vice-versa.