Building long-period SW groundswells
Bali and Mentawais forecast by Craig Brokensha (issued Tuesday 25th September)
Best Days: Thursday onwards
This week through next weekend (Sep 26 – Oct 5)
Bali: The swell bottomed out over the weekend, but today we should be seeing a new mid-period S/SW swell building across magnets and reaching the 4ft range this afternoon (much smaller on the Bukit).
Expect the swell to drop from a similar size tomorrow morning ahead of the first of our long-period SW groundswells due through the coming period.
Thursday's first long-period SW groundswell will be the most consistent, generated over the weekend by a very intense mid-latitude low forming north of the Heard Island region, tracking east towards Western Australia.
Core wind speeds reached the storm-force range and with this, a strong long-period SW groundswell is expected.
A slight upgrade in size is also due, with the swell arriving Wednesday afternoon, building late and peaking Thursday morning to a strong 6ft on the sets, if not for the odd sneaker.
A drop in size should be seen through Friday morning ahead of our very inconsistent long-range SW groundswell arriving into the afternoon and building towards a peak through Saturday afternoon and evening.
This groundswell started to be generated Thursday last week as a very strong storm formed south-east of South Africa, projecting a slow moving fetch of severe-gale to sometimes storm-force W/SW winds through our distant swell window.
The storm pushed further east towards the Heard Island region before breaking down yesterday, with the long-period and very inconsistent SW groundswell now heading through the Indian Ocean towards us.
The forerunners are due to arrive Friday with an afternoon increase in size to 4-5ft+, building further Saturday and reaching 6-8ft at swell magnets through the afternoon, peaking overnight and easing from a similar size Sunday.
Looking at the expected winds over the coming period and we've got a relaxation of the trades and with this each morning should see variable breeze, with more S'ly winds into the afternoons, reverting back to the S/SE-SE from Friday through Sunday.
From Monday next week though we should see E/SE trades proper kick back in, possibly swinging more SE later week but more on this Thursday.
Our next increase in swell will be out of the S/SW, with multiple pulses from this direction as a series of vigorous polar fronts develop south-west of WA, with the first possibly being the most significant.
We're expected to see a very significant polar low forming between Heard Island and Western Australia, generating a large long-period S/SW groundswell for late next week/weekend, but more on this Thursday.
Ments: The surf should be bottoming out across the region today, but our initial pulse of long-period S/SW groundswell is due to fill in tomorrow, kicking to a strong 5-6ft, easing back through Thursday.
The larger and more powerful long-period SW groundswell is due to kick very strongly through Friday, reaching 8ft on the sets by dark across magnets, with a peak Saturday to a similar size, if not for the odd bigger cleanup.
From here we're looking at a steady easing trend through Sunday and early next week, smaller through the end of the week and weekend.
This will be a result of the S/SW groundswell energy for Bali being generated too far east and mostly out of our swell window.
Our persistent and fresh SE-S/SE winds are due through the entire period, favouring more protected breaks, and becoming strong through the weekend before easing off next week.