It's not actually just an Australian term for a hurricane. It's a special type which occurs in the outback, when a swirl of wind picks up wind or sand and spins it around tornado-like. This is very small scale and lasts from about 5 seconds to about 10 minutes.
"Oh look, it's another willy-willy startin' up behind the shed"
A willy-willy is like a wet willy, but instead of putting your finger in your mouth first, you put it in your own ear and wiggle it around first to get a nice coating of wax. Then you insert it into someone else's ear.
Jeff: I'm going to give you a willy-willy, Willy.
Willy: I don't want one.
Jeff: Then your parents shouldn't have named you Willy.
Nickname given to bales of marijuana thrown overboard or out of airplanes. Origin is reportedly from members of the US Coast Guard in the area of Southern Florida.