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Review April |  Swellnet analysis

Review April | Swellnet analysis

For most of the country, the past two weeks have felt like Groundhog Day, both in terms of surf and weather.

A large, slow-moving high-pressure system dominates the mid-latitudes, resulting in brutal showers on the east coast and no real sea breezes, while Victoria sees winds coming from the east rather than the west.

But why does the high move at a snail’s pace from west to east?

It’s thanks to a significant split in the upper jet stream – which drives our weather – as it approaches the continent from the Indian Ocean. This split directs upper level winds to the south and north of the country, and has been that way for a week or two. If there is no upper-level wind between the split, high pressure can form and persist as long as the jet stream remains split.

The current split jet stream (Weatherzone)

The reason for such a significant split is unknown, but it is one piece of the puzzle regarding the current synoptic setup across the country.

The blocking high pressure continued into May, but there was plenty of surf in the weeks before that, so let’s look at the month of April that just passed.

April was a varied surfing month across the country. From terrible flatness in the west to good to great waves on the Surf Coast and everything in between on the east coast.

Moments of brilliance in Sydney (Gavin Vanderplank)

The Western Australian region experienced a seemingly impossible series of small to minor breakers with persistent offshore winds. Surfers living elsewhere may have seen some of it when the Margaret River Pro ran mid-month. The Southwest, which is rarely flat, struggled to provide contestable surf for more than a week before finally showing some form on the final day.

The Surf Coast came to life for most of April as a stationary junction of the Long Wave Trough set up camp just east of Tasmania, driving and strengthening the polar fronts beneath the land. While the wind generally came to the party, it wasn’t all perfect, with many southerly attacks thrown into the mix thanks to the track of the polar fronts across Tasmania rather than coming from the west, all thanks to the aforementioned slow moving treble. pressure system just west of the Bight.

The high was also the cause of the series of small waves in WA, which dominated the month, as shown below in the average sea level pressure (difference from the long-term average) graph for the month.

Mean sea level pressure anomaly for April (NOAA)

That big red spot shows that the pressure in the region was 12 hPa higher than normal, a pretty significant outlier for April and especially in that region, while the yin to the yang was the low pressure anomaly southwest of New Zealand.

As the wind turns counterclockwise around the high winds, we can see the blocking effect of the high waves on Western Australia’s swell window, while also identifying the driver of persistent southerly swells for Victoria, South Australia and Tasmania , along with smaller and inconsistent southerly swells for the big waves. East Coast.

One downstream beneficiary of this setup was Fiji, with endless days of swells pounding the reef at Cloudbreak, with one such swell reaching the XL range.

The graph below, which measures the wind anomaly for April, summarizes the general wind pattern.

Deviation from average wind speed and direction for April (NOAA)

Looking more specifically at the east coast, the start of the month started with a bang in the southern regions thanks to a deepening coastal trough, a low pressure system that brought big surf from the E/NE, followed by four days of pumping southeastern swell when the low deepened and slowly moved towards New Zealand.

Southeast Queensland saw episodic pulses of localized trading swell and long-range easterly energy, culminating in a steady diet of waves, punctuated by a few pumping sessions.

Down in Tasmania the swell was plentiful due to the position of the southern storm track, with numerous sessions on the deepwater flats and more locally around the South Arm. Tassie’s east coast has performed well overall, but has been patchy compared to other surrounding regions.

Jughead and a Cloudbreak Bomb (Tony Harrington)

As we transition into May, the high pressure that dominated Western Australia has slowly shifted eastward, creating off-season easterly winds for the Surf Coast, along with persistent rain and south-southeast winds on the east coast.

Questions are emerging about when this pattern will break and it seems likely that it will happen by the end of the month, but there are a few weeks between now and then. So sit back and learn to deal with this persistent pattern of surfing and weather.