The whale watching season in Sydney is quite long (May-November), but it is not always very busy.
Here is a chart with weekly humpback whale sightings in Sydney between 2010 and 2012 :
And here is a chart with monthly whale sightings in Sydney in 2010-2012:
It is clear visible two peeks in the season. In June/July humpback whales migrating North for breeding in the waters of the Coral Sea. From end of September until December they are going back South to the Antarctic feeding ground for the southern hemisphere summer. At this time of year females with new born calves usually are seen closer to the shore. End of June/July and then October is probably the best time of year for whale watch in Sydney.
August looks like quite month in this chart, but is not because there are no whales. It is the middle of winter and sea can be rough and you won’t have much fun to be on the boat, so some whale watching tours are canceled because of weather during this period. Whales are still there, as not all whales migrating like humpback whales. The Southern Right Whales do not migrate North or South, they usually move along the coastline seeking places to mate and shelter with their newborn calves. This year you even could see Southern Right whales in Sydney harbor:
In Sydney you can see other kind of whales too, but are much rare then Humpback whales or Southern Right Whale. Some people are lucky to see very rare Bryde’s whales, killer whales (or else known as Orcas), also False Killer whales, Minke whales. You most likely also will see Pacific and Bottlenose dolphins.
What time of the day is better for whale watching in Sydney?
Five years ago it was huge difference between morning and afternoon sightings as you can see in this chart.
It probably was just a glitch in sightings recording as by looking to whale sightings of 2010-1012 it doesn’t matter when you go.
It is almost the same in the morning or afternoon. I think it is because most whales are not staying around Sydney but migrating and you can see them when they passing by and time of day is not so important.
Whale sightings numbers for above chart are taken from this page https://whalewatchingsydney.com.au/sightings/index.php?year=2012. I just decided put numbers into more convenient form.
Southern Right whale in Sydney harbor was taken by Tammy.