Our waves are little. Sometimes they are bigger with longer period if there's a cyclone goes past the Kimberley or pass north of us. Most of the time they are from more persistent winds.
We are at the red dot (Casuarina Beach, Darwin). The beach faces pretty much directly north-west. It is about 60 km directly north to the islands. And there are other islands in the gap.

There is mostly only ever small cross chop/wind chop that comes from the north-NW. The only swell that gets in can surely only come from the west.
As in the above pic, this arvo the winds are mostly offshore south-easterly. It has been for a good few days. Even swinging to a more humid north-easterly.
This arvo there was the usual northerly cross chop, but also some longer period (small) waves coming from the west.
Now, that swell surely is not coming all the way in from some system in the Indian Ocean and pushing all that way in across those shallow waters against those prevailing easterly winds (correct me if possible?)
So, could they be from the easterly winds to the north of the islands, and refracting almost 180degrees into us?

Any swell prediction gurus out there?