Effective from: Fri 17 May '13, 09:37AM

Forecast prepared by Ben Matson.
Next update Mon 20/5 5pm.

Previous day's summary:

Tiny residual swells and offshore winds padded out most of Thursday. A small southerly swell is currently building across south facing beaches, with offshore winds continuing.

Forecast period ahead:

The low developing in the lower Tasman Sea has thrown a few curveballs our way in the latest model runs. It's still expected to be quite broad in coverage, and slow moving in nature (both of which are ordinarily very good for NSW swell prospects) however we're seeing a small impediment creep into the synoptic charts, in the form of a ridge of high pressure, well to the south of the low (between Tasmania and Antarctica).

This is squeezing the low in such a way that the southerly extend of its western flank - the region that would ordinarily generate swell for us - is expected to be focused less meridionally aligned (north-south) than previous model runs suggested. What this means is that rather than generating straight southerly swell for the region, the waves we see at the coast will have had to spread back towards the coast, which will result in a loss of size.

Fortunately, most of the swell production will still happen close to the mainland so wave heights have only been slightly downgraded across Sydney and Hunter regions, however locations south of about Wollongong will be positioned inside the swell shadow of the far SE corner of the state (i.e. around Green Cape), so we will see even smaller wave heights across the Far South and South Coasts until Monday (when a secondary pulse originating from polar latitudes will fill in).

Winds will remain offshore throughout this time frame, so conditions should be clean at all but the most exposed south facing beaches. The Hunter region won't fare quite as well though, because of its coastal alignment, however protected spots in this region should see some small waves. Maximum wave heights are likely to reach 4ft at Sydney's south facing beaches on Saturday morning, with bigger sets in the Hunter, easing to somewhere in the 3ft+ range for Sunday, Monday and even possibly early Tuesday (again, a little bigger in the Hunter each day).

Expect most open beaches to be a couple of feet smaller due to the swell direction, with protected southern corners seeing very small waves. Conditions will remain clean throughout however the best conditions will occur on Monday as the low moves away from the coast and light winds settle across the coastal margin.

With the low moving slowly towards New Zealand during this time frame, we'll see diminished swell production within our swell window into the first half of next week - but not ceasing completely. This should maintain small clean waves through into Wednesday at open beaches.

Looking further ahead and we have some exciting weather developments in store for mid-late next week. There is good agreement across the models that an East Coast Low will form off the South Coast sometime later Wednesday, leading to a rapid increase in large, short range (and probably windy) SE swell across most locations for Thursday. Let's pin down the specifics in more detail on Monday.