South-east Queensland and Northern NSW by Craig Brokensha (issued Monday 13th July)

Best Days: Experienced surfers only protected spots Wednesday through Friday, Saturday, Sunday, Monday

Recap

A fun mix of E'ly trade-swell and NE windswell for the weekend, while a new pulse of inconsistent S'ly groundswell filled in across NSW yesterday afternoon, with it holding into this morning to 2-3ft on the sets.

This week and weekend (Jul 14 - 19)

We've currently seeing the first developments regarding the significant low that's due to form in the Tasman Sea this week, with a surface trough deepening off the southern NSW coast. An upper cold pool is also sitting above the state and the trough will feed off it as the trough moves into the Tasman.

Over the coming 36 hours we’ll see the formation of a broad area of low pressure in the Tasman Sea (not classified as an East Coast Low), with it now expected to ‘bomb’ (discussed in more detail below).

Regardless of the classification, we’re set to see a significant and prolonged swell event out of the S/SE this week, easing only gradually into the weekend as the direction swings more SE.

So through this evening we’ll see a broadening fetch of strengthening E/SE winds developing on the southern flank of the low, but this will only move into our swell window early tomorrow morning.

With the central pressure forecast to drop from 1014hPa to 988hPa in the 24hour period from 7pm today to tomorrow, the low will ‘bomb’ and as it does so, an explosive fetch of severe-gale to storm-force SE-S/SE winds will develop on top the growing sea state generated by the strengthening winds before it. This will occur through tomorrow, giving the Mid North Coast an upper cut into the late afternoon/evening.

A slight weakening and broadening of the low is due Wednesday but we'll still see an elongated fetch of SE gales aimed through our south-southeastern swell window with core winds likely being a touch stronger as embedded lows rotate around the main centre.

Looking at the expected trend in size, and Tuesday morning will be small with some background S'ly groundswell to 2ft or so across NSW, tiny across the Gold Coast as the E'ly swell fades.

Through the day though we'll see a rapid escalation in size as the low develops, with strengthening morning W/SW winds, giving into a strong to gale-force S/SW change. Size wise a late afternoon kick to 8ft+ is likely across the lower Mid North Coast, if not bigger on dark, while this trend will be delayed to the north and likely only building on dark, if that around Byron.

The oversized S/SE groundswell event from the core winds slingshotting up the coast is due Wednesday with the Mid North Coast likely to see maxing 12ft+ surf across exposed breaks, more to 10-12ft across the Ballina/Byron region while the Gold Coast looks to kick to 6-8ft across exposed breaks (possibly bigger cleanup), though the points will be smaller and to 4-6ft or so on the outside (smaller inside). The swell may be a touch undersized at dawn, though unlikely.

The Sunny Coast will see the swell arrive through the mid-morning and kick to 4-6ft across open beaches, much smaller inside southern corners.

Winds look favourable as the coast sits north of the lows axis with fresh to strong W/SW breezes across the Mid North Coast, moderate to fresh W-W/SW further north, shifting S/SW into the afternoon.

A slight drop in swell is expected Thursday owing to the low broadening and weakening a touch, but I can't see south swell magnets across NSW dropping below 8-10ft, especially with another local projection of S/SW gales up the coast during Wednesday. The swell looks to swing a little more south in direction, and this will see the Gold and more so Sunshine Coast dropping more noticeably in size.

Exposed breaks on the Goldy are still likely to be 6-8ft, but the points smaller and to 4-5ft on the outside, smaller inside and back to 4-5ft on the Sunshine Coast. Winds will remain favourable for southern corners with a moderate to fresh W/SW-SW breeze (lighter from Ballina north), swinging S'ly into the afternoon.

From Friday we should start to see the size easing though still 8ft+ across NSW in the morning (smaller across the Gold Coast and Sunny Coast), owing to an upper level ridge cradling the low throughout the whole week as it slowly weakens, moving off slowly east through Saturday but more so Sunday.

With this we'll see winds on its south-western flank weaken through Wednesday evening, while over towards New Zealand, a Cook Strait fetch of E'ly gales will develop, persisting into Thursday and Friday but dropping to strong in strength from Thursday afternoon.

A reinforcing E-SE groundswell will be seen from this source, filling in Saturday and keeping Northern NSW around 6ft to occasionally 8ft, with some mid-period S/SE energy also in the mix, 6ft+ across exposed breaks on the Goldy and 4-5ft across the outer points. An easing trend should be seen later in the day but more noticeably from Sunday as the size and period drop, with easing sets from 4-6ft across northern NSW, 4-5ft across the Goldy.

Coming back to the local winds and we'll see fresh to strong S/SW breezes Friday, tending SW across selected locations through the morning but S'ly into the afternoon, while as the low pushes east and weakens, we'll finally see lighter offshore W/SW-SW winds Saturday morning ahead of E'ly sea breezes.

Sunday will then see winds tend NW to NE favouring the more exposed beaches, which will still be solid.

More on this and any changes to the outlook on Wednesday.