July in Review
July was a month of contrasts, where the East Coast swell tap turned off and the southern states saw an uptick in swell activity, though it was very westerly in direction and came with plenty of wind, rain, and even snow.
The seemingly endless run of swell that kept the East Coast active through summer and autumn (thanks to La Niña) came to a close just before the middle of the month. This was after a prolonged E/NE swell episode at the start of the month, originating from a slow moving trough line through the Tasman Sea (dubbed the 'Trough Block' by Ben Matson), followed by a deep Tasman Low the next weekend.
As the swell from the Tasman Low departed around the 13th, west-northwest winds kicked in, quelling activity in the Tasman and Coral Seas.
This shift in patterns was due to a progression of mid-latitude frontal systems firing up and into Western Australia, tracking fairly zonal (moving west to east) in nature across South Australia, Victoria, and then New South Wales.
This is clearly visible on the Mean Sea Level Pressure Anomaly charts for July which show the difference in pressure compared to the long term climate average. Blue to purple indicate lower than normal pressure, and yellow to red, higher than normal pressure.
That big purple low pressure anomaly stretching from Western Australia to Tasmania tells the picture, with the drawn out west to east nature and slight tilt to the east-southeast showing the track of frontal systems through July. Also the big blocking high south-east of Madagascar kept Indonesia relatively quiet until the end of the month when swells pushed up past the West Australian coast.
If we compare this to the classic polar frontal progressions we usually see during winter, which project from the south-west, up and across the country, the main difference is the trajectory and resultant swells.
What we had instead was west. A bombardment of mid-latitude systems across Western Australia brought relentless onshore winds, heavy rainfall, and large, stormy swells which even impacted the central west, while then dragging moisture from the north-west Indian Ocean (under Indonesia), down and across the south-east of the country.
With the lack of polar air being advected up from polar fronts, South Australia saw it's second warmest July on record while still providing the wettest July since 2016. The fronts were just cold enough to provide big snow dumps though, and the rain shadow effect of these south-east sliding fronts across Victoria, Tasmania and New South Wales can be seen in the rainfall anomaly charts.
Anywhere west of the ranges captured all the rainfall, with Gippsland, south-east Tasmania and anywhere east of the dividing range missing out as the air descended and dried out.
As for surf, the swells came in west and stormy across the South Australian Mid Coast, with protected spots fairing best around Victor Harbor, while the Victorian region saw a good proportion of favourable conditions for regions both east and west of Melbourne but with moderate-sized westerly swells.
This was looked upon fondly by the Surf Coast faithful (though some complaints can still be heard regarding the lack of surf over 6ft), while winds stayed north enough to provide plenty of options on the peninsula and Phillip Island.
Tasmania didn't offer much in the way of solid surf days in the South Arm with the mid-latitude frontal activity being positioned too far north of its swell window. The West Coast copped a battering with the bombardment of swell and wind.
If we look at one final chart and that's the average (mean) wind direction and strength throughout the month, we can see the westerly influence across Western Australia, tending west-northwest through the Bight and then north-west across Victoria. The lack of westerly winds in the roaring forties and furious fifties under the country is also apparant.
Also, with this constant flow of relatively warm air from the north-west across New Zealand, it experienced it's warmest June and July on record.