hi tash and dan
for climate stats on rottnest:
www.bom.gov.au/climate/averages/tables/cw_009038.shtmlor here
www.bom.gov.au/climate/data/ and zoom in to rottnest lighthouse
you'll need to look at the wind strength v direction pdfs to understand what MDSX is talking about above
for tide and wave data, i won't assume you're familiar with this just because you posted on seabreeze
www.transport.wa.gov.au/imarine/rottnest-island-tide-and-wave.aspyou really need to start checking it daily and get a feel for how the sea and swell translate to conditions on the water if you want to be proficient out there.
also, don't under estimate what a 1m sea from 25kn easterlies (ie wind waves heading out to sea in the morning) can do to your vessel if you're inexperienced - can be quite hairy once you hit the outer part of cockburn sound and deeper waters despite it looking like glass at leighton.
ditto the 2m seas we can get from a couple of days of 30kn SWers in the afternoons.
if in doubt, sit it out. but otherwise play safe and enjoy!