Oversized south swell incoming
Sydney, Hunter and Illawarra Surf Forecast by Ben Matson (issued Monday 17th January)
Features of the Forecast (tl;dr)
- Very large, dangerous S'ly swells building Tues PM, holding Wed
- Wind affected conditions Tues, improving steadily through Wed
- Light winds plus strong though easing S/SE swells Thurs/Fri
- Fun weekend of waves
- Lots of tropical potential long term
Recap: S’ly swells built strongly on Saturday from 2-3ft at south facing beaches early, up to 3-5ft by the afternoon. Wave heights then maintained 3-4ft through Sunday morning (coupla bigger sets across the Hunter), easing a little into the afternoon, before rebuilding to 4ft again this morning, then easing once more this afternoon. Beaches not open to the south were much smaller. Saturday’s conditions were clean across most coasts with early offshore winds, however the Hunter saw disjointed surf thanks to a southerly fetch sitting just offshore (local wind obs were offshore, though). Sunday morning provided super clean conditions with early offshores, ahead of a swing in the wind to the south late morning. Light offshore winds this morning preceded an afternoon sea breeze from the NE.
This week (Jan 19 - 22)
We’ve had a model upgrade for our approaching large southerly swell.
This is mainly due to the deepening rate of the primary low contained with an amplifying Long Wave Trough (see below). The low is 'bombing' upon entry to our south swell window - ‘bombing’ means the central pressure of the low drops more than 24hPa in 24 hours, and as a result of such a significant drop in surface pressure, the winds around the low are approaching storm force strength.
The latest ASCAT observations (satellite winds) are picking up a broad fetch of 50kt winds south of Tasmania (see below). Winds of this speed are not uncommon within typical frontal cycles, but they’re usually found throughout a very small region of a tight core low. The difference this time around is that the current fetch of 50kts is much broader in spatial coverage, and it’s also tracking NE into the lower Tasman Sea through our south swell window, creating a ‘captured fetch’ scenario which further amplifies the resulting swell size compared to regular low pressure systems.
Amazingly, the low is expected to maintain strength for another 24 hours, though it will slowly edge out of our swell window during this time.
The upshot of the stronger winds, captured fetch, and extended period of gales in our south swell window means all of the numbers discussed on Friday (and indeed, since last Monday) have been increased.
Don’t worry too much about Tuesday though.
Surf size will start off relatively small, and a gusty southerly change will cross the coast early morning, rendering most locations quite bumpy. South facing beaches should manage choppy 3ft+ surf early but the afternoon will herald a step-ladder upwards trend of powerful, overlapping southerly swells that should push north of 6ft+ by early afternoon and probably 8-10ft+ by close of business.
Also, it's kinda obvious but the South Coast will pick up this increase earlier; locations further north will see a later arrival. So I'll add in observations to the comments below as they come to hand.
Because of the large periods associated with this event (peak swell periods should be up around 17-18 seconds), offshore bombies that enjoy southerly swells will magnify wave heights considerably. Don’t be surprised if your Instagram feed lights up with images of hellmen riding bombs in the 12-15ft+ range.
Wave heights will plateau overnight Tuesday and into Wednesday morning, before slowly easing through the afternoon. Conditions will improve a lot into Wednesday as winds slowly abate, though the synoptic flow will remain S/SE. We should see isolated pockets of lighter SW winds here and there but it won’t be enough to iron out all of the bumps from Tuesday’s onshore.
As for surfable options through this swell event, most locations will be overpowered. Protected spots will be a lot smaller so only the most sheltered points and southern corners will offer workable conditions. And keep in mind there’ll be a large amount of water pushing through the lineup, with dangerous sweeps showing at most locations.
So, Tuesday afternoon and Wednesday will not be suitable for inexperience.
The backside of this swell looks the pick anyway. Because of the slow moving nature of the parent low through the lower Tasman Sea this week, we’ll see the swell direction trend more to the S/SE and ease gradually in size. Therefore, Thursday should still be somewhere near 6ft+ at south facing beaches (occasionally 6-8ft+ at the bombies and south swell magnets like the Hunter), but we’ll see size lose a foot or so into the afternoon and then another foot or two into Friday.
Thursday will offer great conditions in the morning under a light offshore breeze, ahead of afternoon NE sea breezes. A developing synoptic northerly flow into Friday will start to create some unwelcome lumps and bumps but early Friday morning should still provide a window of clean-is conditions with light N/NW winds as the swell continues to gradually fade.
This weekend (Jan 23 - 24)
We’ve got some fun waves ahead this weekend.
Friday’s easing S/SE swell trend will continue into Saturday, with early 3ft+ sets at south facing beaches abating to 2ft+ through the day. We’ll see some small NE windswell in the mix too with sets around the 2ft mark.
Conditions are looking pretty good, with a weak trough off the South Coast disrupting Friday’s northerlies, and allowing early light winds (though afternoon NE breezes are likely).
Similar conditions are expected on Sunday, though a small new long period S’ly swell is expected to grace the coast, generated by an impressive frontal progression south of the continent from Wednesday thru’ Friday. It’ll be very directional in nature and probably only favourable for a handful of south swell magnets, but we could see inconsistent 3ft sets at south facing beaches, up to 3-5ft across the Hunter.
More on this in Wednesday’s update.
Next week (Jan 25 onwards)
Looks like a lot of tropical activity on the boil for the Coral Sea into the long term, which bodes well for both a steady supply of trade swell next week (peaking through the second half) and also some potential cyclone activity. Plus the usual spin-offs into the northern Tasman Sea as well.
Thumbs up all round! See you Wednesday.