fFshing off the beach at whatipu is nowhere near as dangerous as the rest of Auckland's west coast beaches, the manukau bar protects it from the worst of the swell. As mouth said the beach beside nine pin is a good place to start and at low tide it's easy to cast into the channel as it's really close (also means you don't have to wade in). The current there can be really strong when the tide is running so it's usually best to pick a day when the tidal difference between high and low is small. Also don't bother if the swell is any more than 1.5m as it's all just too messy. Also don't bother if the wind is any more than 15 knots as its damn annoying. The time of day doesn't seem to make much difference (except that your more likely to catch sharks in the dark). Likely catches here are kahawai and trevally and occasionally a gurnard at slack tide (kingys, small sharks, spotty dogs and snapper are also a possibility). Use a 4 or 5oz breakout sinker with a running rig or pulley rig, even that will not hold when the tide is running. Best bait to use is mullet as its nice and tough and can stand up to the current, if you use pillies then make sure you tie them on with a lot of bait elastic. I wouldn't worry too much about going there by yourself at this time of year as it's highly likely that there will be other people fishing out there. Even so always watch the sea and just use some common sense.
This spot is not a consistent producer of fish but it's a nice easy introduction to west coast surfcasting and it can sometimes turn it on, and if the fishing's crap on the day then at least the scenery is outstanding.
I've had my best days surfcasting a few hundred metres up the beach from ninepin when I landed 15 kahawai in a couple of hours with the largest going 3kg, was awesome.
If you're going to try the kaipara then mossie bay is at the end of south head rd, steep track straight down, fish it about 2-3 hours either side of low. It's best to go to the left or right of the bay as there seems to be a shelf right in front that will lose you a lot of sinkers and mess up your line. Shelley beach wharf is supposedly a hotspot for gurnard but I've only ever caught small sharks there, I think it fishes best on an incoming tide from about half tide in.
Good luck