Nias, Mentawai, South Sumatra forecast by Craig Brokensha (issued Tue 15th Jul)

Best Days: Later Wednesday onwards

This week and weekend (Jul 16 - 20)

It's been a slow few days across the Ments with the swell bottoming out leaving only exposed swell magnets with small waves.

We should see a lot more activity from tomorrow afternoon though as the forerunners of a large pulse of S/SW groundswell fill in later in the day.

This groundswell was generated late last week and through the weekend by a couple of vigorous polar fronts pushing up from south-east of South Africa, over the Heard Island region under the influence of the Long Wave Trough.

The swell should fill in overnight Wednesday and peak through the day Thursday to 8ft across exposed breaks in the Ments, with 10ft sets rolling through every now and then. South Sumatra will be bigger with some bombs to 12ft likely, and Nias can expected a touch less size compared to the Ments.

Winds in general look to be good for this swell with a variable airstream expected across most regions through the peak of the swell as well as when it eases through Friday and the weekend.

Wave heights will slowly ease on the back of Thursday's large S/SW groundswell and likely bottom out through Sunday to 3-5ft across exposed spots in the Ments.

Next Monday onwards (Jule 15 onwards)

The storm track will be focussed more towards Bali and WA over the coming days and this will result in us only seeing moderate sized + pulses of side-band S/SW groundswell energy through next week.

A fun pulse is due on Monday coming in at 5-6ft across exposed breaks in the Ments before backing off slowly through Tuesday and Wednesday. We may see a similar sized pulse later in the week, but we'll look at this again on Thursday.

Longer term there are some indications that we may see a large and powerful S/SW groundswell Wednesday week, but this is a long way down the track and will be closely monitored over the coming days.

16 day Mentawai forecast graph
16 day Nias forecast graph
16 day South Sumatra forecast graph