Nias, Mentawai, South Sumatra forecast by Craig Brokensha (issued Tue 27th May)

Best Days: Thursday onwards

This week and weekend (May 27th – Jun 1)

Today and tomorrow will be the low points in swell activity over the coming period, with some decent waves due from Thursday onwards.

A couple of new SW groundswell pulses are due Thursday and then later Friday, but more so Saturday across the region. The first has been produced by a strong mid-latitude storm pushing fairly north into the Indian Ocean. This swell should be fairly consistent and peak through Thursday to 5-6ft at exposed spots in the Ments, with a touch less size in Nias and a few bigger bomb sets around Southern Sumtra.

A secondary larger but much less consistent swell generated by a flurry of strong polar frontal activity in our far but favourable swell window to the south-east of South Africa and Madagascar is due to arrive later Friday and peak Saturday.

Satellite observations confirm peak winds speeds around 45kt at the strongest stage of the progression, with long-period energy due to arrive through Friday ahead of the bulk of the swell on Saturday. The Mentawais should see solid 6-8ft+ waves Saturday with similar 6-8ft waves around Nias and 8ft to occasionally 10ft sets at exposed spots across Southern Sumatra.

There will be very long waits between sets for this swell, and generally light variable winds creating good waves across most spots. A drop in size should be seen through Saturday afternoon and further Sunday but not below the medium to large size range.

Next Monday onwards (Jun 2 onwards)

Into next week there's nothing too major on the cards, with a reinforcing SW groundswell in the 5-6ft range around the Ments Monday expected to slowly tail off through the week and be padded out with smaller S/SW groundswells.

Longer term the storm track will remain active to the south-east of South Africa, with a couple of good SW groundswells on the cards from Friday onwards next week, but we'll review this Thursday.