I read where some translators believe that "forty" is just a way for the ancient Hebrew to refer to an unspecified, large number. In other words, "40 days" would just be an idiom for "many days."
We do the same in English. If someone is looking at a large flock of birds, they might exclaim, "There must be a million birds there!" They don't literally mean that there are 1,000,000 birds, it's just a way to explain that this is an unusually large flock of birds. Or if someone tries to lift a box full of books, they might say, "This thing weighs a ton!" when the box is probably only 40-50 pounds, far short of 2000 pounds.
Anyways, that's just one interpretation of the word "forty" in the Bible. I'd have to study to see if there is any real significance to the number 40 in the Hebrew language.