Riding at a peak in July | Swellnet Analysis

It’s the middle of winter, but instead of writing an analysis article about a major cold snap in the Southern Ocean, the opposite is happening: a near-record high pressure area is forming over the main swell window of southeastern Australia.

For surfers, low pressure areas may get the most attention, but lately it’s the high pressure areas that have been making headlines. This is largely due to the jet stream splitting over the Indian Ocean, which in turn results in anomalous, slow-moving high pressure areas over the continent. Without a higher airflow to ‘push’ it past the high pressure areas themselves and become a blocking high pressure area.

The significance of the upcoming blocking setup can be put into perspective as it is predicted to come very close to the highest pressure ever recorded in Australia, which occurred in Launceston, Tasmania on 7 June 1967 when it measured 1044.3 hPa.

The two major global weather agencies GFS (American) and ECWMF (European) predict that the air pressure over Tasmania will reach 1044 hPa this Thursday and possibly also on Saturday.

Average sea level pressure (GFS) anomaly for this Thursday, with parts of Tasmania possibly reaching 1044 hPa

Whether the pressure is record-breaking or not, its impact on the next two weeks of surf will be felt everywhere.

South Australia and Victoria will see off-season and persistent winds from the north-east and east-west quadrants respectively, along with no significant swell sources. This will be due to the self-described blocking effect that the high pressure will have on approaching frontal systems from the Indian Ocean, deflecting them southeastwards towards the polar shelf.

Although the Surf Coast doesn’t have much to offer here, you can still get a few days of surfing at the more exposed locations, which is rare in winter.

It’s all about the beach holidays in Victoria (Arklay)

It is also worth noting that with the significantly higher than normal sea level pressure, we will see correspondingly lower tides. This is due to the inverse barometer effect where sea level falls by 10cm for every 10hPa increase in pressure above the ‘normal’ 1013hPa. For Tasmanian locations the sea level fall will be a very noticeable 30cm, 25cm+ in Victoria and between 20-25cm in Sydney and surrounds.

Margaret River will also benefit over the coming week as the western arm of the high pressure brings offshore winds along with large swells from the frontal activity coming in from the Indian Ocean. However, this will go pear shaped from the weekend as the high pressure shifts slightly further east, exposing the region to weak, northwesterly winds.

On the east coast we are currently seeing the eastern arm of the building high bringing polar air, showers and variable levels of south-southeast swell which will be more easterly next week and beyond as the high moves further east into the Tasman Sea. Onshore winds will be a problem for much of the coast.

The strong and slow movement of the high pressure area will itself produce a long-lasting, moderate easterly trade wave, but as a bonus, increasing tropical activity in the Coral Sea looks set to accelerate the wave action, creating larger waves from next week onwards.

Winds look tough at first and there will be a lot of rain, but we can expect an inland trough to move east and along the coast over the weekend of 14/15, bringing cleaner conditions and drier weather.

In July 2022, there was also a deepening tropical low pressure area generating strong, off-season easterly waves (Brokensha)

One final point worth noting is where the eastern influence of the high lies, and the low pressure activity beyond it. With the high extending from Western Australia to New Zealand, a corridor of low pressure has opened up on the east coast of New Zealand, with a series of significant polar storms feeding the groove. Right in Teahupoo’s main swell window.

We are looking at a large to possibly extra large southwesterly ground swell event for mid to late next week, just a few weeks before the Olympics that begin on July 27. At this distance it will probably be out of reach for paddling, but it will catch the eyes of the world – not to mention the Olympic surfers.

Severe gale force to storm force winds targeted at Tahiti and Teahupoo in particular

Stay tuned to the comments below for updates on how this important synoptic event will unfold.