Indonesia swell: Bigger than Muzza
We're right in the thick of an overactive swell period across the Indonesian archipelago, not to mention southern Australia.
A very large long-period S/SW groundswell is currently filling in across most locations, with pumping waves for the Rip Curl Cup, and while it's the biggest swell so far this year, we're looking at an even bigger swell next week.
As discussed in last week's article, the south-east Indian Ocean is experiencing the most active storm period in years due to consecutive nodes of the Long Wave Trough moving through the region.
The second node was forecast to be the strongest and most northerly protruding of the two, and we're now seeing this come to fruition with the biggest swell of the season so far due to hit Indonesian and West Australian coasts next week.
This node is expected to move very slowly east and effectively stall just west of Western Australia while reaching a peak in intensity, directing back to back storms more northward towards Indonesia, rather than eastward under Australia as was the case with the activity earlier this week.
With the node protruding further north than normal, we'll also see these storms push much further north in latitude, reaching a line drawn west from Ningaloo. This all points to a more consistent swell event for Indonesia, along with less size loss due to swell decay.
Looking at the structure of the frontal progression, and a mid-latitude storm has created an active sea state for a vigorous polar front to generate an expansive, slow moving fetch of severe-gale to storm-force winds over.
The fetch will remain near stationary while a secondary intensification will project storm-force winds north-east at a similar speed to the swell it's producing (known as a captured fetch) an over a very large open ocean sea state.
Under a captured fetch scenario we see faster and larger than normal wave growth and this will help push this swell into the XXL range with forerunners of 21 seconds, with the bulk of the groundswell coming in at an amazing 18-19 seconds.
This will produce very large and dangerous surf across most exposed locations (the largest of the season), building through Tuesday and likely reaching 10-12ft+ late in the day across eastern Indonesia, peaking Wednesday morning to 12ft to possibly 15ft.
The swell should impact the Mentawai islands only a couple of hours later, with magnets kicking to 10ft to likely 12ft on dark, peaking Wednesday morning to 12ft+.
The last swell of this magnitude was the June 2015 Murray Close (Muzza) swell. Comparing the two, this swell will have a touch more south in it, yet it'll be bigger for eastern Indonesia, pushing above the heights of three years ago.
For Western Australia, most, if not all, of the swell will go to waste, owing to the position of the Long Wave Trough just off the coast, bringing strong to gale-force onshore westerly winds.
Following Tuesday/Wednesday's XL swell event, follow up oversized groundswells are expected late week and into the following weekend, continuing the run of exceptional Indonesian swell.
For any changes to the timing and sizes regarding this swell, keep an eye on the Indonesian and regional Australian forecaster notes.