A fortnight ago we discussed the tropical wave of activity know as the Madden Julian Oscillation (MJO) and its expected strengthening and movement from the Indian Ocean, east across northern Australia into the end of this month.

This followed a strong episode of southerly swell from a 'bombing low' at the entrance to the southern Tasman Sea, over-performing across some regions, while under-performing in others. As predicted, the MJO is currently intensifying across north-eastern Australia with it forecast to strengthen further across the Western Pacific, lingering there into mid-February.

The chart below shows where the MJO has been around the Earth (at tropical latitudes) through the end of December (purple) and January (red). The perspective is that of looking from the North Pole with the MJO currently strengthening in the Western Pacific Ocean (to our north-east) since January 21st.

It's forecast to intensify slightly further while hanging around the Western Pacific (our medium-range eastern swell window), triggering the coming tropical activity.

MJO forecast (green line), slow moving and strong through the Western Pacific

We're already seeing the impacts of the increase in tropical activity with a tropical low forming in the Gulf of Carpentaria, and another due to deepen adjacent to the Kimberley coast over the coming days.

Looking to our east and north-east though, we've got a ton of swell potential owing to said tropical activity in the vicinity of Fiji and Tonga. What we're looking at is a couple of healthy high pressure systems moving into the Tasman Sea just east of New Zealand on the weekend as the tropical depressions deepen to the north.

Source: Bureau of Meteorology

As the tropical activity continues to strengthen, it'll drift south, squeezing and tightening the pressure gradient on top of the cradling highs, setting up a very healthy trade wind flow towards northern NSW and southeast QLD, extending into the Coral Sea.

This alone would generate a great run of moderate-sized easterly trade swell for mid-late next week onwards, but when we add in the strongest bursts of winds associated with the tropical low(s), larger pulses of easterly groundswell are expected across the entire East Coast.

Looking at the timing and we should see building levels of easterly trade swell across northern NSW and SE Qld from Tuesday, with any groundswell from the stronger embedded wind bursts due into Thursday/Friday. The groundswell will be better aligned for southern NSW and arriving around a similar time late week.

Locally, winds are still dicey with a couple of possibilities, but for the northern regions it looks like winds will be variable as the swell builds and then freshen from the south-southeast late week as a broad ridge of high pressure moves in across the country from the west.

With the MJO remaining active into the middle of the month we're likely to see swell activity persisting into the following week across the East Coast, but keep an eye on the local Forecaster Notes for a more accurate idea on the specifics like timing, local winds, and longevity.

For the rest of the country the coming pattern isn't favourable as the highs block Southern Ocean fronts while bringing onshore winds for Victoria and South Australia. Western Australia will be windy and cleaner, but swells look generally subdued aside from the odd larger outlier.