Just using the water availability currently known on earth, the concept of a world flood looks impossible. So why is there not enough water today to re-produce a worldwide flood? How was the preflood earth different? What was the atmosphere like that it could produce a 40 day and night global rain? Were there oceans back then or was it all up in the "canopy" of the stratosphere?
First some speculation (the meaning part only is at the end of this post) --
Putting aside many other questions, like was the flood regional or is the flood story a combination of real events and additionally parable like parts, and other questions, and only just for speculation considering the idea of a world flood -- it is physically possible (with caveats).
And just for a moment, not yet looking for what is much more important, the
actual meaning of the story!! (see bottom of post for more on that).....
To get a flood appearing to be locally as experienced on the ark, and vast also, both, you don't have to have more water, just a very great amount of water the planet already has temporarily in some places it isn't normally, and just the fact of the slope of the land being gentle will allow that standing water to last a very long time, and in
some places much longer than others, for instance.
More, it's possible also by physics and known events. For instance.
If a
water ice comet hit the deep pacific ocean, at the right angle, and was the right size comet (such typically would come in at various random angles), it would cause a vast amount of ocean water to be vaporized without even hitting the mantle under the water, vastly more water vapor than normal, and then you'd get both world wide cloud cover and world wide precipitation, rainfall around the world, and lasting weeks.
That's all physically possible, if just the right comet was sent on just the right angle.... (yes I know this is sort of beside the point to many of us!
For me it brings to mind the great extinction of 66-65 million years ago.
A large asteroid or comet hit the Earth, and it was
just the right size and at just the right moment in Earth's history to cause most dinosaur species to become compost.
Bigger = wipes out mammals too.
Smaller = leave many more dinosaurs continuing.
Just the right size.
Leading to the rise of mammals.
Just right. This is what comes to mind for me. The real meaning of the flood story, though, and the reason it is in the Bible, it's 0% about mere history, mere physics, mere evolution of species, etc., etc., etc.
0% of the real meaning.
It's about mankind and our hearts and souls. In Genesis chapter 6, key, crucial verses we need to notice every word in are verse 5 and verse 11 (but better to read through, so you get things like verse 6 also). Notice that exact wording -- "all", "every", "only", "all the time"..."full"....
Think on that. It's not saying 'mostly'. It's saying all, every, only, full, total complete. 100% (or including Noah, maybe that's really 99.99999% or whatever).