I'm actually in perth now, and will be here until next year, i have a friend, currently doing ADAS part 3 in TUCF, he's finishing up by next week.As to the weather, october would be spring time, surface temp would be somewhere around 12-30 degree celcius.As you go along, it would be very hot even to the 40s. summer=december=flies
Ive been diving here for quite some time, u/w temp is usually around 15-18 degrees, its the same be it winter, summer and whatnot. But I'm no commercial diver, just a leisure diver.I think its gonna be colder if you're 40 meters down.
A bit on fremantle,
It's a small harbour town,30 mins driving to perth, very calm on weekdays, but can be very crowded on weekends, very laid back, everything is very slow paced, although there's a night club in town. you can literally lay down on the streets at night

. A lot of eateries, flea markets, there's also a diveshop near the seaport authority. its called Diveskisurf, if i'm not mistaken, lots of shore diving spots, transfer jetty to Rottnest Island, lots of fishing spots as well. A lot of things to discover in fremantle really, but the best thing is, you dont have to drive, everything is within walking distance, well almost. That's all I can think of for now, if you need more assistance, I'm more than happy to help, just leave a msg.
give me a buzz when ure in town!