Sealing a Garage door during hurricane flooding
I don't know that there's a practical way to do this (at least, not in a way that doesn't impede future use of the door). If you don't care about the door (or at least would consider some door repair as an acceptable result), I would suggest the following


Buy some really good outdoor caulk (mineral spirit cleanup) and caulk the sides, bottom and first panel breaks from the bottom. Be liberal and make sure you cover all the joints in their entirety (this will take a fair amount of caulk)
Sandbag in front of the door 18"


The major caveat here is that 12-15" of standing water (let alone wind driven water) is going to be hard to keep out entirely, especially with something not designed to be waterproof. Expanding foam isn't really a good choice here because, while it is waterproof, it's also porous, and only deigned to prevent incidental water exposure, not standing water. With sandbags and caulk you might stand a chance, but it's far from certain.

As to cleanup, you'll have to cut the caulk and scrape the door clean, which will almost certainly damage the paint/finish of the door and maybe the outside frame. Be prepared to repaint the entire door after doing this.