In Noah's Ark myth God sent 40 days of rain to flood the Earth. Are any such long periods of persistent rain recorded? What kind of disaster could happen to cover all continents with water?
The talk.origins archive documents an extensive list of claims about the flood. It also includes sections discussing the Ark and the various problems that aspect of story has. There's also a separate article dedicated to the flood.
Are any such long periods of persistent rain recorded?
I don't know about persistent rain, but Seattle has had 30 days of measurable rainfall twice in the past 60 years. It isn't unreasonable to believe that other locations could have had a longer, more aggressive chain of storms, and it's also not unreasonable to expect that there'd be problems with local waterways flooding as a result.
What kind of disaster could happen to cover all continents with water?
There are a few frequently suggested sources of the water. They all fail simple tests. If there was supernatural involvement, we'd also expect to see global evidence of a great flood, but this is absent.
The most logical explanation given the lack of evidence is that the story is mythical.
As @Sklivvz posted in the comments the flood story probably originates from part of the Epic of Gilgamesh which follows the same general plot. The resident deity is upset with humanity and selects one righteous man to be saved. Instructions are given to build a large boat to save all of the animals and the man's family. It rained, though only for six days. Birds are sent out, one doesn't come back, a mountain is found, a sacrifice is made, the resident deity is pleased / remorseful and promises not to do that again.
The talk.origins site hasn't been updated in a while. There was some evidence uncovered somewhat recently that suggested that the myth may have originated when the Black Sea grew rapidly after an influx of water from the Mediterranean in ~5600 BCE. In 2009, National Geographic published a follow-up that suggested the growth in the Black Sea was not as catastrophic as first thought, and might not really be the origin of the myth.
Given the time this was written, how would anyone know that all the continents were flooded? Let's just assume that the World was flooded, and that the World was considerably smaller. Horizon-to-horizon flooding happens, and if that's all you can see, that means the whole World's flooded.
Although unrelated, the same applies to pairs of "every single animal". This could well be just goats, sheep, chickens and dogs.
A point often missed about the Noah myth is that it doesn't claim the flooding was all due to rain. It says "the fountains of the deep were opened". Still, this CYA attempt fails, because there isn't enough water on the planet to cover all the land. Even if all the ice on the South Pole melted it would only raise sea level about 60 meters (200 feet).
I observe 4 questions here:
- Could a Great Flood have happened?
- Are 40-day-periods of rain recorded?
- What kind of disaster could happen to cover all continents with water?
- Can the Noah's Ark myth be correct? (implicit)
- The smaller your universe is, the bigger a flood is. If you don't know that Africa, Europe, Asia, America and Antarctic exist, it's impossible to know that the whole earth is covered.
- I'm sure so; see Charles about Seattle. Investigate weather stations in regions of rain periods.
- To cover Himalaya, Alpen, Anden, Appalachen, Rocky Mountains and so on: Not enogh water. But from rain apart, tsunamis, smelting ice, river outbreaks (rain elsewhere) cause dramatique floods.
- If you know 500 species, most of them small, you can imagine them to fit into a big ship. Today, we know how many different animals there are, and that you need much bigger groups, to have enough genetic diversity to let one survive. But of cause predators need other animals as meal as well. To put all of them, and enough food on a ship, the ship would need to be multiple times the size of the Maracana stadium. So it's just a story.
It seems likely that there was a flooding event of some sort which contributed to this legend. Probably the best candidate is the "Black Sea deluge", an event that is believed to have occurred around 5600BC.
What supposedly happened is that the Mediterranean Sea broke through the Strait of Bosporus and flooded the Black Sea (which was, prior to this, much lower than it is now).
The sea, though low, was still quite large, and it's not implausible that there were farmers along its shore who had fairly large boats. Some of these could well have seen the waters rising and herded numbers of their livestock onto their boats to escape the flood.
Note, though, that this theory has numerous critics, and definitive proof is lacking.