Gnaraloo tides

Just check the Gnaraloo tide forecast on this site:

www.seabreeze.com.au/graphs/wa4.asp#F0GNAR

Tides obviously go up and down every day and are driven by the moon. Biggest variation typically after the full moon.
Most of WA does have somewhat weird tides because it faces dead west.
Atmospheric pressure also affects tides. Low pressure = higher tides, High pressure = lower tides.

DIamond
If you want to get serious about riding waves read up on tides, check out the sites that register tides around the spots you like and see the differences in low tides throughout the months. BUT because it may have been a series of low tides last september does not mean it will be the same this september. Also learn on times, i.e. lows at lunch with an incoming tide equals goodie good good as generally the waves will get better trhough the arvo when the breeze hits.
There are a lot of spots that will own you at gnarloo. especially if light wind. last time i was up a guy went to go out at kite beach, very light, obviously not very experienced. tide was also very low. he headed downwind toward bombie, came in and no-where to go bar the flat reef with about 1m cliff to stumble up and over to get onto sand. he was lucky and made it without too many cuts.
If you aint been there before, watch it for a while, watch how guys go out, look at the reefs, look at the reefs at all tides. it isnt like perth where we barely have 1m tide generally, there is more, a lot more. the further north you go the more you get.
Learning to read conditions enters a whole new stoke to the sport - get into it.

p.s. you may want to check availibility for september/october, it is probably fully booked already.