I have tried to pick the common weather conditions that prevail in Sydney and list the dive sites that could be suitable in those conditions.

GENERAL ADVICE

Open Ocean

My experience is that any winds over 15 knots from all but the west or north-west are unsuitable for boat diving. For 10 to 15 knots a lot of caution is needed. Any on-shore winds over 10 knots would also make most shore diving in the open ocean unsafe.

Harbour and Bays

Shiprock, Lilli Pilli, Camp Cove, Parsley Bay and Clifton Gardens are normally suitable for diving in all weather conditions (subject to tidal limitations at Shiprock) and are about the only places worth trying when the weather is bad. If more than 100 mm of rain has fallen in the past four days, forget even these. Apart from this limiting factor, these sites are always suitable and not included in later comments.

SOUTHERLY WINDS AND SEAS (includes SE and SW)

10 to 15 knots - 2 to 3 metres
Shore Dives
The open ocean would be undiveable except at Shelly Beach, Fairy Bower and South Maroubra. Inside the bays you could probably dive at Bare Island Right, Inscription Point, The Monuments and possibly Oak Park.

Boat Dives
Middle Ground, Six Fathom Reef, Pizza Reef, Barrens Hut out of Port Hacking, Inscription Point, Anchor Reef, GT Reef, Henry Head out of Botany Bay, The Gap, The Colours, Red Indian Point, South Head, SS Royal Shepherd out of Sydney Harbour would probably be okay. The SS Annie M. Miller could also be possible, but extreme care should be taken.

You could also probably dive inside Henry Head in Botany Bay.

Do not run north as you may have a lot of trouble getting back if the winds and seas get worse.

15 to 20 knots - 3 to 5 metres
Shore Dives
The open ocean would be undiveable except at Shelly Beach, Fairy Bower, and The Monuments, although even this last site may be not safe

Boat Dives
Only Six Fathom Reef at Port Hacking and perhaps Inscription Point out of Botany Bay and Red Indian Point in Sydney Harbour. You could also try The Container Wall in Botany Bay and Inside South Head and Sow and Pigs in Sydney Harbour.

Over 20 knots - 4 to 7 metres
Stay in bed.

NORTH EASTERLY AND EASTERLY WINDS

5 to 10 knots - 1 to 2 metres
Shore Dives
Bare Island is suitable for all strengths of NE and E winds as is Bass and Flinders. The open ocean would be marginal in many places. You could possibly dive Fairy Bower (E okay), Shelly Beach should be okay, Oak Park would probably also be okay as would Inscription Point. The Monuments would be good, especially in E winds. The Voodoo shore dive (not the dive I cover in this site) would be starting to become diveable.

Boat Dives
Most locations would be okay but you would not want to run into the NE for too long. If there is a NE wind when heading out and it is forecast to get stronger, if you must go a reasonable distance, head NE into the wind so that if it gets stronger, you will be running back with it.

15 to 20 knots - 3 to 5 metres
Shore Dives
Bare Island and Bass and Flinders would still be okay. The open ocean would be very unsafe. You could probably not dive Fairy Bower (E marginal) but Shelly Beach should be still okay. Oak Park is probably not okay. Inscription Point and the Monuments would probably not be diveable (but E winds may be okay). The Voodoo shore dive should now be possible.

Boat Dives
North Head would be a good place to dive as would inside North Head. In E winds, it would be rough here but you could still probably dive here. The entrance to Botany Bay would also be okay on the north side, with Henry Head (including inside) good and Minmi Trench a bit rough but diveable, although Minmi would be bad in E winds. Out of Port Hacking, Six Fathom Reef would probably be the only place to dive, although it would be very choppy.

Over 20 knots - 4 to 7 metres
Stay in bed except for Bare Island, Voodoo shore dive, Bass and Flinders and all the harbour dives.

NORTH WESTERLY OR WESTERLY WINDS

5 to 10 knots - 0.5 to 1 metres
Shore Dives
Westerly and north-westerly winds tend to flatten out the seas dramatically. However, it may take a day or more to cut the swell right down if it has be running at over 2 metres. Assuming that the wind has been running for more than a day, you should be able to dive most locations, although very hard places like Shark Point and Mahon Pool may still be a bit too rough.

Boat Dives
You should be able to dive all locations except perhaps ones right close to the rock platform.

10 to 15 knots - 0 to 0.5 metres
Shore Dives
Most places should be okay, with Shark Point and Mahon Pool now diveable.

Boat Dives
You will need to stick within a few hundred metres of the shore for comfort, although wrecks like the SS Myola and the wrecks at Long Reef will be starting to get a little uncomfortable.

15 to 20 knots - 0 metres in close
Shore Dives
All locations should be okay, but it will probably be too rough to get in off the western side of Bare Island. This is the time to dive Shark Point and Mahon Pool.

Boat Dives
Perfect for diving in close to the rock platform, the seas should be absolutely flat. The further out reefs and most of the wrecks may still be diveable, but you will need to run along the shore and then out to these sites. It will be uncomfortable at these sites and it could be too rough.

Over 20 knots - 0 metres in close
Shore Dives
All locations should be perfect, but it will be too rough to get in off the western side of Bare Island. This is the time to dive Shark Point and Mahon Pool.

Boat Dives

Unless the site is close to the shore, do not head out as you may get blown to New Zealand when the anchor rope breaks or the anchor comes free (as it probably will). I would not consider diving places like the wrecks at Long Reef or the Myola, reefs at the entrance to Sydney Harbour or Botany Bay, the SS Tuggerah or SS Undola.

It may even be too uncomfortable to drive the boat across Botany Bay from the only accessible boat ramps and even Sydney Harbour and Port Hacking will be very rough in spots.

RESOURCES

There are a number of resources where you can check the weather and forecasts for Sydney. I have links to the best ones on my weather page. Click here to see it.