With Sydney’s unpredictable weather always have a ‘Plan B’ in case of rain. Think of a venue that caters for both indoor and outdoor ceremonies, so if it rains you can easily move undercover and there won’t be the fuss and drama of having to contact all of your guests to notify them of another location. If there is no alternative, make sure you have big, golf-sized umbrellas on standby.
On the other hand, usually rain and heavy cloud formations can provide epic location images and stunningly romantic photographs... So it may just work out in your favour.