Java, Bali, Lombok, Sumbawa forecast by Craig Brokensha (issued Tuesday April 15th)
Best Days: This evening onwards but only for experienced surfers
This week (Apr 15 - 18)
The coming forecast period is quite exciting with a couple of medium-large S/SW groundswells due over the coming days ahead of the first large groundswell for the season over the weekend.
A moderate increase in long-range S/SW groundswell is due today, but a larger and stronger increase in swell is due tomorrow with a peak expected later in the day. This swell was generated last week in the Heard Island region by a vigorous polar low, with a peak in size to an inconsistent but strong 5-6ft due tomorrow evening across exposed spots. There's the chance for the odd bigger sneaker set in the mix, but these will be rare.
The swell should drop back a touch in size on Thursday but a reinforcing S/SW groundswell will help steady wave heights keeping 4-6ft waves hitting exposed locations for most of the day. A more pronounced drop is then due overnight and into Friday morning.
Winds in general are expected to be light and variable over the coming week, with weak trades trying to develop each afternoon but not really reaching any major strength or persisting overnight.
This weekend onwards (Apr 19 onwards)
The first pulse in a series of large S/SW groundswells generated by an amplification of the Long Wave Trough across WA's South West is due to arrive strongly later Friday afternoon, peak overnight and hold good size into Saturday morning.
The Long Wave Trough steers and supercharges polar fronts up to where ever it is focussed and currently we're seeing a series of vigorous frontal systems falling under the effects of this upper atmospheric weather feature.
The first system was a tight but strong mid-latitude pushing in towards WA's South West yesterday and should kick up 6ft+ waves across exposed spots later Friday, that will then ease from a similar size Saturday morning.
Of much greater importance is a very large and powerful long-range S/SW groundswell due on Sunday generated by a vigorous and broad polar front that's fired up west of Heard Island, and has already generated a fetch of gale to severe-gale W/SW winds.
This system will maintain its strength through today and tomorrow while pushing north-east towards WA before slipping into Australia's shadow on Thursday morning.
Size wise we're expecting to see very large 10ft waves across exposed locations with 12ft sets in the mix. Swell magnets may even see the odd bigger bomb!
The swell should drop slowly through Monday but the morning is still expected to see 8ft+ waves at exposed spots, with smaller 4-6ft waves on Tuesday.
A reinforcing S/SW groundswell is due Tuesday afternoon generated by a trailing front behind the huge system responsible for Sunday's swell, but this system will be much smaller in size and generally a touch weaker.
Still another pulse to 6ft+ is expected before easing gradually into the end of the week.
Winds on Sunday will continue to be variable during the morning ahead of a weak afternoon trade-flow, with slightly stronger trades developing through the middle of the following week.
East Java Forecast