(This is part of a game I'm making, with a bit of backstory here.)
Size/Shape: Roughly oblong and quite large. Length of 15 miles, and a greatest width of 8 miles.
Placement: 500 miles south of Perth, Australia.
Environmental effect: Due to handwavium reasons, the appearance wouldn't significantly effect the surrounding environment. It can be seen, landed on, all that. However, it won't effect sea levels or anything. It will be sensed by all modern technology and biological functions (of humans AND animals).
Land: It will be covered in a temperate rainforest, in case that helps anything.
Timeline: The appearance of the island takes 6 hours. This finished taking place right "now."
Method of appearance: A thick fog rolls out of the ocean, and over the course of 6 hours, the topmost edges of it seem to solidify into a real island. From below it looks like fog that you can't see through. From the top, like any other island.
So, how and when would an island this size, in that position be discovered?