Sydney Hunter Illawarra Surf Forecast by Steve Shearer (issued Fri Sep17)

Forecast Summary (tl;dr)

• Fun ESE swell Sat AM with good winds, winds tending NE and freshening before a late W’ly change PM
• Small NE windswell in the mix Sat
• Easing size Sun, back to tiny in the PM with a basic W’ly wind pattern
• Possibly large increase in S swell Tues, with Tasman low on the radar, bring strong/gale force S’ly winds
• Large S swell holds Wed, before easing through Thurs/Fri with improving winds
• More S swell next weekend, stay tuned for details

Recap

Yesterday came in well over f/cast expectations with a mix of both SSE swell trains and larger than expected ESE swell. That saw protected and semi-protected spots firing in the 3-5ft range, with S’ly winds slowly laying down through the day. This swell came from a flare up in the cradling fetch as the Tasman low wobbled and semi-stalled before making it’s way towards New Zealand. Today has seen more good to great surf with lighter NW winds opening up more exposed spots, with size ranging from 3-4ft up to 4-5ft on the more exposed Hunter Coast. A continuation of the great run of late winter/early Spring surf.

This weekend (Sep 18-19)

We’re now on the tail end of the swell from this week's Tasman low, with a fun, little sting in the end of the tail expected and some tricky, but largely favourable wind shifts expected this weekend. Read on for details.

Elongated high pressure now covers the Tasman sea adjacent to the East Coast, with a pressure gradient squeeze expected to intensify over the next 24 hrs as a trough and front approaches from the west. That will see N’ly winds freshen overnight and into tomorrow, possibly with a slight NNW or NW tilt to the direction before they tend N’ly again and freshen. There’ll be swell in the water from the ESE, mid period swell generated by a flare up of the low later Thursday and some NE windswell from the local fetch off the coast. This is expected to be in the 3-4ft range, with an easing trend through the day. As the trough and front passes through there’ll be a wind shift, expected later in the day with winds tending WNW'ly late in the a’noon.

Models do show an area of SW winds, which is expected to reach Ulladulla/Jervis Bay, but there is a chance it could extend north to there Sydney basin through the PM. Keep tabs on your local wind obs Sat PM, but offshore winds should make for some fun waves in the PM with the mix of ESE swell and NE windswell, likely in the 3ft range. 

Sunday sees plenty of action as far as wind changes go. Winds are likely to tend W through W/SW early and be mod/fresh in strength. Synoptically the area then sits in a bit of “dead air” between two high pressure cells with a trough just offshore. This is likely to see a period of NW to NE winds through the middle parts of the day before we come under the influence of synoptic W/NW winds through the PM hours. A last little pulse of well angled ESE swell from the Cook Strait fetch today provides some mid-period surf in a fun sized package with some inconsistent 3-4ft sets. This swell is likely to back down quickly through the day so get into mop up mode early Sunday. 

One last swell source is possible Sun, with a fetch of W’ly winds exiting Bass Strait Sat PM. At present models show windspeeds maxing at strong wind/low end gale level- which is at the bottom end required for a Bass Strait fetch to produce anything meaningful due to the refraction back to the coast from such an off-axis fetch. 

Despite that flukey nature of the source fetch, it may produce a few stray 2-3ft sets, more likely on the Hunter, through Sun a’noon. 

We’ll update in the comments if it looks better through Saturday. 

Next week (Sep 20) and beyond

Another very dynamic week ahead and with major model divergence between the main weather models it’s likely we’ll be back in here with revisions on Mon.

We’ve got a series of fronts and deep Tasman lows passing through, with an unstable troughy pattern in the Tasman sea. This pattern is being anchored by a large high which is expected to become slow moving in the Bight early next week and maintain tight pressure gradients with fronts and a possible low in the Tasman.

Monday will be the low point of next week, so we can book that in for a lay day. Pre-frontal winds maintain a NW flow through the day, possibly tending to light NE seabreezes before a more serious SW wind change in the a’noon as a trough and front impact the Tasman sea. A few stray 2 ft sets  in the morning will drop right back to tiny surf during the a’noon. 

Tuesday is where life gets very interesting for the Tasman sea. The crux of the matter is a major front pushing NE up into the Tasman, an upper cold pool coming through the interior, interacting with a lingering trough line. On it’s own terms the front itself is likely to see strong to low end gale force SSW to S winds develop along the NSW Central Coast and bring a steep increase in local S swell. 

GFS (and other) models develop a low in the increased vorticity between the advancing front, cold pool, and lingering trough, likely just off the Hunter Coast. Under this scenario, severe gale to storm force winds rapidly develop just off the coast in a broad fetch extending from north of the Hunter to the far south coast. 

This would see a rapid, step-ladder increase in S/SSE swell during Tuesday with gale force S’ly winds accompanying the building swell as the coast hugging low reaches storm force. Under this scenario we’d be looking at surf building into the 8-10ft range during the a’noon at exposed S facing stretches, bigger 12ft+ on the Hunter. This is a potential severe weather event in the making.

This size would likely be holding into Wed, with the low slowly drifting away, with continuing strong to gale force S’ly quarter winds confining surfing to the most sheltered and novelty spots, where size would be much smaller.

Keep in mind under the EC scenario we are looking at a much more modest swell event.  A mix of S swell trains building through Tuesday, likely into the  6ft range with fresh S’ly winds and a much steeper roll off in size through Wed and into Thursday. 

A broad easing trend is likely under both scenarios through the end of next week, with winds likely to ease and tend offshore as any Tasman low of frontal feature migrates eastwards and pressure gradients ease.

Into next weekend and further strong low pressure systems under Australia are expected to generate more S swell for the region, potentially long period and quite sizey. With so much instability and short term dynamism on the charts we’ll flag next weekend for at least moderate S swells with most major models showing S’ly component winds in the central and lower coast of NSW as fronts push northwards along the coast.

Don’t put the step-ups and guns away just yet. Have a great weekend and check back Mon for a fresh analysis of next weeks developments.