Step 12: Ready for the rain
Obviously, the hood is open on the end, and this is not waterproof! It is only going to protect the lens if you don't point it up into the rain. And you will have to gauge the seal on the bag for yourself (it's your camera after all). I will use this in a downpour, and simply keep the lens pointed horizontal or down! If you take this out in a hurricane, you'd better be pointed downwind!
That said, you can also see from the way the diameter shrinks as it moves closer to the body of the camera, that any drips that get inside the large end will be prevented from flowing back into the lens assembly, unless you tip it way back.